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  • Column liquid chromatography  (495)
  • Angiosperms  (221)
  • Humans
  • Inorganic Chemistry
  • Springer  (722)
  • 1990-1994  (722)
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  • 1
    Digitale Medien
    Digitale Medien
    Nucleotide distribution in gymnosperm nuclear sequences suggests a model for GC-content change in land-plant nuclear genomes (1994)
    Springer
    Journal of molecular evolution 39 (1994), S. 34-46 
    Details
    ISSN: 1432-1432
    Schlagwort(e): CpG suppression ; GC content ; Angiosperms ; Isochores ; GC bias ; Mutational pressure ; Error-prone repair ; Transcriptionally coupled repair
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Nuclear protein coding sequences from gymnosperms are currently scarce. We have determined 4 kb of nuclear protein coding sequences from gymnosperms and have collected and analyzed 〉60 kb of nuclear sequences from gymnosperms and nonspermatophytes in order to better understand processes influencing genome evolution in plants. We show that conifers possess both biased and nonbiased genes with respect to GC content, as found in monocots, suggesting that the common ancestor of conifers and monocots may have possessed both biased and nonbiased genes. The lack of biased genes in dicots is suggested to be a derived character for this lineage. We present a simple but speculative model of land-plant genome evolution which considers changes in GC bias and CpG frequency, respectively, as independent processes and which can account for several puzzling aspects of observed nucleotide frequencies in plant genes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00178247
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  • 2
    Digitale Medien
    Digitale Medien
    Enantiomeric resolution of anti-HIV agents on a cellulose derivative chiral stationary phase (1994)
    Springer
    Chromatographia 38 (1994), S. 57-61 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Enantio separation ; ChiralcelR OJ ; Anti-HIV agents
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Anti-HIV enantiomeric 1H, 3H-thiazolo[3, 4-a] benzimidazoles have been stereospecifically analyzed by elution on a column of cellulose tris-(4-methyl-phenylbenzoate)ester adsorbed on macroporous silica (ChiralcelR OJ). The enantiomeric resolution of the compounds examined is linked to a complex and competitive contribution of different factors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02275727
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  • 3
    Digitale Medien
    Digitale Medien
    Control of adsorption and solubility in gradient high performance liquid chromatography. Part 3. Sudden-transition gradient elution of styrene/ acrylonitrile copolymers (1994)
    Springer
    Chromatographia 38 (1994), S. 749-755 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Copoly(styrene/acrylonitrile) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Copolymers from styrene and acrylonitrile could be separated according to composition by gradient elution through methanol after injection inton-heptane and sudden addition of 50, 60, or 70 vol% tetrahydrofuran. The peak sequence was the same as with a common binary gradientn-heptane/tetrahydrofuran, i.e., retention increased with acrylonitrile content of the samples. With copolymers containing 37, 31, or 26% acrylonitrile, the elution characteristics in the ternary systems could be logically extrapolated towards the points measured in the corresponding binary gradient system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269631
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  • 4
    Digitale Medien
    Digitale Medien
    Chiral recognition of structurally related aminoalkylphosphonic acid derivatives on an acetylated beta-cyclodextrin bonded phase (1994)
    Springer
    Chromatographia 38 (1994), S. 771-775 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chiral recognition ; Aminoalkylphosphonic acid derivatives ; β-cyclodextrin bonded phases
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An acetylated β-cyclodextrin column was used to analyse the enantiomeric resolution of a number of aminophosphonic acids. Effects of the structure of these compounds on the extent of separation was examined. Molecular modelling studies were also carried out in an attempt to relate any interaction between the amino and phosphonic acid groups to chiral recognition by the stationary phase.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269635
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  • 5
    Digitale Medien
    Digitale Medien
    Application of liquid chromatography-particle beam mass spectrometry and gas chromatography-mass spectrometry for the identification of metabolites of polycyclic aromatic hydrocarbons (1994)
    Springer
    Chromatographia 38 (1994), S. 781-788 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Gas chromatography ; Particle beam MS detection ; Polycyclic aromatic metabolites ; Biodegradation in water
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Two liquid chromatography-particle beam mass spectrometry (LC-PBMS) systems have been used for analysis of polycyclic aromatic hydrocarbon metabolites in water samples from a biological decomposition model experiment. The results were compared with those obtained by classical gas chromatography-mass spectrometry. Evaluation of spectral data indicated the presence of six main metabolites; 1H,3H-naphtho [1,8-cd]pyran-1,3-dione, 1-(hydroxymethyl)naphthalene, and 1,2-acenaphthenedione were identified by use of standard substances and spiking experiments. Enrichment of the investigated water samples with online pre-column (C18) concentration, freeze-drying, and solvent extraction led to similar results with only slight differences. The application of microbore separation columns proved to be a promising tool in particle beam LC-MS measurements.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269637
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  • 6
    Digitale Medien
    Digitale Medien
    Solid phase extraction applied to the determination of biogenic amines in wines by HPLC (1994)
    Springer
    Chromatographia 38 (1994), S. 571-578 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Wine ; Biogenic amines ; Solid-phase extraction ; Derivatization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A method suitable for the determination of 19 biogenic amines in wine has been developed. The method involves derivatization of amines by treatment with dansyl chloride and solid-phase extraction of the derivatives. Prior to the derivatization procedure, clean-up of the wine sample with polyvinylpyrrolidone is carried out. Reversed-phase gradient elution HPLC with UV detection at 250 nm was used to determine these compounds. Some consideration was given to the effect of temperature on the separation process. Linearity of derivatization was obtained for amounts of all the biogenic amines ranging from 500 μg·L−1 to 20 mg·L−1. Limits of detection (signal-to-noise ratio=3) of the amines were similar for all the dansylderivatives (between 50 and 150 μg·L−1). Addition of standard amines was used for the determination of amine recoveries. These were better than 85% for ethanolamine, tryptamine, phenetylamine, putrescine, cadaverine and histamine. The overall process was succesfully applied to identify and quantify biogenic amines in white and red wines.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02277156
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  • 7
    Digitale Medien
    Digitale Medien
    Relationship between retention behavior and molecular structure in HPLC. Correlation between solubility parameter and molecular properties (1994)
    Springer
    Chromatographia 38 (1994), S. 599-608 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Solubility parameters ; Structure parameters
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The application and significance of the solubility parameter are detailed for chromatographic systems. A critical review of the general concept and several empirical and semi-empirical equations for the solubility parameter are reported. Using the basic theory and a systematic study of the main factors affecting total (or expanded) solubility parameters (δT) along with boiling points and molar volumes, we found correlations between four kinds of solubility parameter obtained by different methods, which unify their calculation and establish an equation for the calculation of δT, successfully applying it to retention prediction in GC and LC. The results show our approach is more accurate and simplifies to a two-parameter model involving fundamental physicol-chemical parameters. In addition, the variation of δT with the carbon number of homologous series was investigated, mathematical models were derived by multi-regression analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02277161
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  • 8
    Digitale Medien
    Digitale Medien
    Separation of L-(+)-ascorbic and D-(−)-isoascorbic acids on multimodal phenylpropanolamine-coated silica (1994)
    Springer
    Chromatographia 38 (1994), S. 609-612 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Multimodal chromatography ; L-(+)-ascorbic and D-(−)-isoascorbic acids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A mixture of L-(+)-ascorbic acid and its epimer, D-(−)-isoascorbic acid, have been separated on a phenylpropanolamine-coated silica support using multimodal chromatography. The retention order of the diastereoisomers is the same as that found in reversed-phase mode in which ionic interaction is predominant. Applications of such columns to the analysis of L-(+)-ascorbic acid in an ascorbic acid injection formulation and an orange juice sample are vigen.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02277162
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  • 9
    Digitale Medien
    Digitale Medien
    Enantiomer separaton of tifluadom and analogues by liquid chromatography with cellulose-based chiral stationary phases (1994)
    Springer
    Chromatographia 38 (1994), S. 629-632 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chiral/enantiomeric iseparation ; Cellulose-based chiral phases ; Tifluadom analogues ; 2-acylaminomethyl-1,4-benzodiazepines
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The resolution of nine recamic mixtures of tifluadom analogues has been evaluated using the chiral stationary phases Chiralcel OD and Chiralcel OJ. The separation was performed on an analytical scale to optimize the conditions for chiral resolution, approaching baseline separation, of the two enantiomers. Eight racemates were baseline separated on Chiralcel OJ using a mobile phase of hexane/2-propanol.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02277166
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  • 10
    Digitale Medien
    Digitale Medien
    Retention and selectivity of aromatic hydrocarbons with mono-substituted polar groups in ternary RP-HPLC systems (1994)
    Springer
    Chromatographia 39 (1994), S. 67-70 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Reversed phase systems ; Ternary eluents ; Mono-substituted aromatics ; Retention and selectivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The variation in selectivity for aromatic hydrocarbons with mono-substituted polar groups is investigated in ternary mobile-phase systems on C18 stationary phases. The dependence of log k′ on the proportions of two modifiers was determined for the solutes within the concentration range of ternary systems obtained by mixing two binary eluents: methanol + water and tetrahydrofuran + water or acetonitrile + water and tetrahydrofuran + water. The nature of the relationships is explained in terms of molecular shape, molecular interactions between solute and extracted modifier and the ordering of solvated ligands on the stationary phase.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320460
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  • 11
    Digitale Medien
    Digitale Medien
    The simultaneous determination of L-697, 661, a HIV-1 specific reverse transcriptase inhibitor, and its 6-hydroxy metabolite in human plasma via column-switching high performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 79-84 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Column switching ; HIV type 1 reverse transcriptase inhibitor ; Acquired immune deficiency syndrome ; L-697, 661
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A method for the determination of L-697, 661, a human immunodeficiency virus type 1 reverse transcriptase inhibitor, and its 6-hydroxy metabolite in plasma is described. Following analyte isolation via solid phase extraction, samples are analyzed by HPLC using a column switching system. Column switching allows each analyte to be simultaneously analyzed under isocratic reverse phase conditions in a run time of 21 minutes. The assay was linear in the concentration range of 10–500 ng/mL for each analyte when 1 mL aliquots of plasma were extracted. The assay has been fully validated and utilized for human pharmacokinetic studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320463
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  • 12
    Digitale Medien
    Digitale Medien
    Reversed phase behaviour of high molecular mass polystyrenes in ethyl acetate solvent mixtures (1994)
    Springer
    Chromatographia 39 (1994), S. 663-667 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Polystyrene ; Ethyl acetate ; Dichloromethane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The reversed phase behaviour of high molecular mass polystyrenes was investigated on C18 bonded phase columns with ethyl acetate-methanol and ethyl acetateacetonitrile mobile phases. The results are compared with the corresponding dichloromethane mobile phases. The ethyl acetate-methanol mobile phase showed anomalous elution behaviour, similar to other previously investigated solvent combinations with methanol. The ethyl acetate-acetonitrile mobile phase showed no anomalous behaviour, increased retention and, elution over a wider composition range compared with the dichloromethane-acetonitrile system. However, resolution between adjacent molecular masses was considerably worse.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274580
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  • 13
    Digitale Medien
    Digitale Medien
    Use of porous graphitized carbon column for determining taxol inTaxus baccata (1994)
    Springer
    Chromatographia 39 (1994), S. 740-742 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Porous graphitized carbon ; Taxol ; Taxus baccata
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Porous graphitized carbon columns have been used for the separation and quantitative determination of the anticancer drug taxol in the bark and foliage ofTaxus baccata. Successful separations were achieved using water∶dioxane 54∶46 v/v eluent. Peak purity tests and the spectra of taxol peaks taken at different retention times indicated that the taxol peak is not entirely homogeneous and probably contains other taxoteres coeluted with the main compound.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274591
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  • 14
    Digitale Medien
    Digitale Medien
    Validation of a strategic approach to high-performance liquid chromatographic method selection (1994)
    Springer
    Chromatographia 39 (1994), S. 339-345 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; First-guess ; Retention optimization ; Validation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A recently reported chromatographic method selection strategy has been validated using fifteen drug formulations selected randomly from the Belgium Compendium, 1992. On the basis of the hydrophobic and the acidic — basic properties of the sample components, reversed-phase was recommended as the first choice mode for all formulations. For two multicomponent formulations the range of analyte polarity dictated the need for gradient elution. The commerical software DryLab G/plus® was used for selection of optimum gradient conditions. The results obtained by both isocratic and gradient chromatography are discussed, as is the usefulness of a tailing suppressor in both modes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274523
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  • 15
    Digitale Medien
    Digitale Medien
    Analysis of oligonucleotides using coupled high performance liquid chromatography-electrospray mass spectrometry (1994)
    Springer
    Chromatographia 39 (1994), S. 405-408 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Electrospray mass spectrometry ; Oligonucleotides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Improved HPLC and ESMS conditions have been established, allowing the separation and analysis of oligodesoxyribonucleotides by coupled HPLC-ESMS.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278754
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  • 16
    Digitale Medien
    Digitale Medien
    Chemical analysis of microcystins RR and LR in cyanobacterium using a prepacked cyano cartridge (1994)
    Springer
    Chromatographia 39 (1994), S. 427-430 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Microcystins RR and LR ; Solid phase extraction ; Cyano cartridges
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A new method for the determination of microcystins PR and LR in cyanobacterium was developed using cyano-type prepacked cartridges. The microcystins were extracted with 10% acetic acid and the extract applied to a Baker 10 cyano cartridge. After elution from the cartridge with 0.5M acetic acid-acetonitrile (1∶9) the microcystins were determined by HPLC. Better recoveries and chromatograms were observed than with ODS cartridges.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278757
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  • 17
    Digitale Medien
    Digitale Medien
    Control of adsorption and solubility in gradient high-performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 557-563 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Copoly(styrene/methyl methacrylate) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Copolymers from styrene and methyl methacrylate (MMA) were separated by both normal and reversedphase gradient chromatography. Both modes could be performed by sudden-transition gradients where the polymers were injected into a non-solvent whose polarity was either rather low (e.g.,n-heptane) or high (e.g., acetonitrile). Then the solvent strength of the starting eluent was rapidly increased to a given level by addition of dichloromethane. Under properly defined conditions, the sample components still remained on the column. Elution could be triggered off by the steady addition of another non-solvent whose polarity was opposite of that of the starting non-solvent. Thus, the mixture of five copolymers with MMA content ranging from 14 to 84% could be separated on a polar cyanopropyl column by injection inton-heptane and elution through acetonitrile (normal phase mode) and on a RP C18 column by injection into acetonitrile and elution throughn-heptane (reversed-phase mode), provided that in both modes about 30% dichloromethane was added to the starting non-solvent. The elution sequence in the reversed-phase mode was opposite to that in the normal-phase mode, obeying the approved polarity rules of chromatography in both cases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02268279
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  • 18
    Digitale Medien
    Digitale Medien
    Rapid separation of polycyclic aromatic hydrocarbons by packed column supercritical fluid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 607-611 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Supercritical fluid chromatography ; Column liquid chromatography ; Polycyclic aromatic hydrocarbons ; Environmental samples
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The separation in 6 minutes of the sixteen US Environmental Protection Agency (EPA) polycyclic aromatic hydrocarbons (PAHs) on a single packed column by supercritical fluid chromatography (SFC) is described and compared to that obtained using liquid chromatography with the same column. Several environmental samples containing polycyclic aromatic hydrocarbons obtained from various sources including soil, water, petrochemicals and coal have been analysed by SFC under optimised conditions. Packed column SFC is shown to be an efficient and promising method for the rapid monitoring of environmental polycyclic aromatic hydrocarbons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02268288
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  • 19
    Digitale Medien
    Digitale Medien
    Salt promoted adsorption chromatography of malted barley amylases (1994)
    Springer
    Chromatographia 38 (1994), S. 232-234 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Thiophilic interaction chromatography ; Hydrophobic interaction chromatography ; Salt-promoted adsorption ; Malted barley amylases
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A sequence for the fractionation of the amylasic components from a malted barley extract is proposed using two salt-promoted, adsorption processes: thiophilic interaction chromatography (TIC) and hydrophobic interaction chromatography (HIC). Two fractions containing α-amylase activity were recovered during the thiophilic chromatography; the first was resolved in to α-amylase I and β-amylase I by HIC on a phenyl-sepharose column; an enrichment factor of 32 was achieved for α-amylase I. The other amylasic component eluted from the thiophilic gel was characterized as α-amylase II. Although the adsorption of malt amylases on phenylsepharose and the thiophilic adsorbent is salt promoted, the interactions involved in each case are clearly distinguished by the different behaviour and disparate salt effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290342
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  • 20
    Digitale Medien
    Digitale Medien
    Syntheses of spherical silica and titania from alkoxides on a laboratory scale (1994)
    Springer
    Chromatographia 38 (1994), S. 291-294 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Column packings ; Silica and titania ; Sol-gel method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A process to synthesize silica and titania as spherical packing materials has been investigated on the laboratory scale by the sol-gel method. The silica and titania obtained were tested under normal-phase separation conditions for comparison of their retention characteristics silica witha a commercial. The silica was found to be similar in its retention behaviour to the commercial silica. The titania showed basic properties and strongly retained acidic compounds.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269770
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  • 21
    Digitale Medien
    Digitale Medien
    Selective and sensitive analysis of 1-nitropyrene in diesel exhaust particulate extract by multidimensional HPLC (1994)
    Springer
    Chromatographia 38 (1994), S. 199-206 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Nitro-PAHs ; Diesel particulate extract ; Column switching
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A multicolumn (MC) HPLC method for the determination of 1-nitropyrene (1-NP) at trace-levels via on-line reduction to 1-aminopyrene and fluorescence detection is presented. On the first column, packed with a pyrenebutyric acid amide stationary phase, the nitro-derivatives of PAHs are strongly retained and separated from other matrix components. The nitro-PAHs-containing fractions are transferred onto a RP18-column via stepwise gradient elution and finally separated according to their various lipophilicities and sizes. To increase the overall selectivity and sensitivity of the multidimensional method (MD-HPLC system) post-column, on-line reduction of the nitro-PAHs to the respective amino-PAHs via a short catalysis column is performed thus enhancing the sensitivity significantly (to low pg levels). The applicability of this method for the determination of trace amounts of 1-NP in real samples (diesel particulate extracts) is demonstrated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290337
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  • 22
    Digitale Medien
    Digitale Medien
    Synthesis and characterization of phenylpropanolamine bonded silica for multimode liquid chromatography of small molecules (1994)
    Springer
    Chromatographia 38 (1994), S. 485-490 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Multimode chromatography ; Inorganic anions ; Organic acids ; Drugs
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A multimodal silica support carrying both anionexchange and hydrophobic functions was prepared by bonding phenylpropanolamine to epoxysilane-modified silica. This support was characterized with regard to its physical and chromatographic properties and has a surface coverage of 150 μmol g−1. The reversed-phase and the anion-exchange behaviour of the new stationary phase were investigated by injection of acidic, neutral and basic drugs and inorganic anions. The retention of the tested compounds was manipulated by modifying the pH and proportion of organic modifier in the mobile phase in isocratic mode. The mixed-mechanism column provided a flexible and versatile method for the simultaneous separation of neutral, acidic and basic compounds.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269841
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  • 23
    Digitale Medien
    Digitale Medien
    Control of adsorption and solubility in gradient high-performance liquid chromatography. Part 2: Sudden-transition gradient elution of styrene/ethyl methacrylate copolymers (1994)
    Springer
    Chromatographia 38 (1994), S. 559-565 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Copoly(styrene/ethyl methacrylate) ; Gradient elution, sudden transition ; Precipitation chromatography of polymers ; Solubility of polymers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Copolymers from styrene and ethyl methacrylate have been separated according to composition by methanol gradients on a cyanopropyl column after injection inton-heptane and a subsequent rapid increase of dichloromethane (DCM) concentration from zero to a constant value in the range from 10 to 40%. Retention and resolution in sudden-transition gradients increased with decreasing DCM concentration. The gradient rate was varied between 2.5 and 7.5%/min with optimum resolution at 2.5% min. At a level of 20% DCM and a gradient rate of 5%/min, the separation of a mixture of five copolymers in a sudden-transition gradient was the same as with the corresponding common gradient, i.e., with injection into a mixture ofn-heptane and 20% DCM. Elution was also achieved at a level of 20% DCM by continuous addition of tetrahydrofuran (THF) instead of methanol. With THF, the peaks appeared later than with methanol in spite of the fact that methanol is a non-solvent and THF a good solvent for the polymers investigated. This indicates that elution was, in the first instance, caused by the polarity of the eluent. The elution characteristics of the copolymers in the system heptane/methanol at constant DCM concentration were basically similar to the already known characteristics iniso-octane/methanol at constant THF concentrations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02277154
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  • 24
    Digitale Medien
    Digitale Medien
    In-line derivatization method for fluorometric determination of catecholamines by high performance liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 591-594 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; In-line derivatization ; Fluorometric determination ; Catecholamines in urine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A fluorometric method has been developed for the determination of norepinephrine, epinephrine and dopamine by high-performance liquid chromatography. Catecholamines extracted from urine were separated by reversed-phase chromatography with an alkaline mobile phase (pH 8.0, 20 mM sodium tetraborate containing 30 mM 1-butaneboronic acid) and were fluorometrically detected (Ex 400 nm and EM 475 nm) via in-line derivatization at high temperature (100 °C). Retention times for norepinephrine, epinephrine, dopamine and isoproterenol as an internal standard were 8, 10, 13 and 28 min, respectively. Calibration curves for these compounds were linear from 4 to 100 ng/ml standard solution. The detection limit (signalto noise ratio=3) for norepinephrine, epinephrine and dopamine was 0.1, 0.2 and 0.8 ng. The assay of catecholamines in human urine is also described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02277159
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  • 25
    Digitale Medien
    Digitale Medien
    Determination of glutathione in pharmaceuticals and cosmetics by HPLC with UV and fluorescence detection (1994)
    Springer
    Chromatographia 39 (1994), S. 23-28 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Glutathione ; Pharmaceuticals and cosmetics ; Pre-chromatographic derivatization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A selective HPLC determination of reduced glutathione (GSH) in pharmaceutical and cosmetic formulations is described based on prechromatographic derivatization with 4-(6-methylnaphthalen-2-yl)-4-oxo-2-buteneoic acid. The derivatization reaction is rapid under mild reaction conditions (10 min at ambient temperature and pH 7.5) and the excess reagent can be removed by liquid-liquid extraction. The thiol adducts were chromatographed on a C-8 column using 0.05 M triethylammonium phosphate (pH 4.0) — acetonitrile 68∶32 (v/v), as the mobile phase; UV and fluorescence detection (lem 450 nm, lexc 300 nm) were both used. The structure of the thiol adducts was confirmed by1H and13C NMR spectra using sodium methanethiolate as thiol nucleophile.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320453
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  • 26
    Digitale Medien
    Digitale Medien
    Retention parameters of aromatic hydrocarbons with mono-substituted polar groups in binary RP-HPLC systems (1994)
    Springer
    Chromatographia 39 (1994), S. 51-61 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Reversed-phase systems ; Binary eluents ; Mono-substituted aromatics ; Retention and selectivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Capacity factor (k′) values of aromatic hydrocarbons with mono-substituted polar-groups are correlated for reversed-phase systems involving stationary phases with C18 or C4 ligands chemically bonded to silica and a binary aqueous eluent containing modifiers: methanol, acetonitrile, tetrahydrofuran, isopropanol, dioxane or dimethoxyethane. The relative retention variations of the solutes are interpreted with special consideration of their interactions with non-polar stationary phases and the molecular structure of the modifiers and solutes. Rules for retention and selectivity optimisation in RP-HPLC systems are given.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320458
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  • 27
    Digitale Medien
    Digitale Medien
    Chromatographic and related studies of alkylamide phases (1994)
    Springer
    Chromatographia 39 (1994), S. 155-161 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chemically bonded phase (CBP) ; Alkylamide phase ; Surface characterization ; Thermal stability ; Packings evaluation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A series of chemically bonded phases has been prepared with amide groups localized by means of hydrophobic ligands. The physicochemical and chromatographic properties of such phases with chain lengths ranging from C5 to C8 have been examined by porosimetry, elemental analysis, solid-state NMR, and liquid chromatography. Subsequently, the conformational dynamics of these phases have been investigated by analyzing the dependence of the capacity factor (k) on the reciprocal of temperature for different organic compounds. Special emphasis has been given to the reproducibility of retention data obtained before and after temperature-dependent measurements.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274494
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  • 28
    Digitale Medien
    Digitale Medien
    Simultaneous quantitative measurement of a new platelet activating factor antagonist (BN 50730) and its two main metabolites in human plasma and urine by LC-MS (1994)
    Springer
    Chromatographia 39 (1994), S. 228-238 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; LC/MS coupling ; Particle Beam interface ; Plasma and urine samples ; BN50730 and its metabolites
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A simple and sensitive assay has been developed for the quantitative measurement of a new platelet activating factor antagonist (BN50730), and its two main metabolites (BN50727 and BN50922), at the picomole level in human plasma and urine. The three compounds of interest and the internal standard (BN50765) were measured by combined LC-negative chemical ionization MS. A simple solid-liquid extraction procedure was used to isolate the parent drug and the two metabolites. The MS was tuned to monitor the intense ionm/z 333 generated in the ion source by a dissociative capture process. The assay was on 1 ml plasma or 0.1 ml urine and the quantitation limit was calculated as 1 ng·ml−1. The very low relative standard deviations and mean percentages of error calculated for within-day or between-day repeatability assays demonstrate the ruggedness of the technique for routine determination in biological fluids. Some preliminary results on the pharmacokinetics of the parent drug and its two main metabolites illustrate the applicability of this method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274505
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  • 29
    Digitale Medien
    Digitale Medien
    Generation of split-flow micro-gradients for capillary HPLC (1994)
    Springer
    Chromatographia 39 (1994), S. 279-284 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Capillary columns for LC ; Micro-gradient generation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The generation of a micro-gradient for micro HPLC capillary columns is described. The system used is a modified and improved version of a split flow gradient elution device. Gradient tests have been performed and have shown good reproducibility under all conditions. The system has been successfully coupled with a particle beam LC-MS interface and the analysis of a mixture of twenty seven basic or neutral pesticides is reported.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274514
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  • 30
    Digitale Medien
    Digitale Medien
    Separation of chlamydosporol epimers by reversed-phase HPLC using commercial solvent optimisation software (1994)
    Springer
    Chromatographia 39 (1994), S. 443-447 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Mycotoxins ; Chlamydosporol epimers ; Solvent optimisation ; Fusarium species
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Two epimers of the mycotoxin chlamydosporol were separated by HPLC on an RP-18 column using a quaternary mobile phase consisting of water (79.1%), methanol (10.0%), acetonitrile (10.4%) and tetrahydrofuran (0.5%), with a flow rate of 1 ml min−1. This optimal composition of mobile phase, with which the resolution value for the two epimers (1 and2) was 2.73 with retention times of 5.88 and 7.12 min, respectively, was achieved by the application of Philips Solvent Optimisation Software PU 6100. The presence of free silanols on the stationary phase was shown to be an essential requirement for the separation of the chlamydosporol epimers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278760
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  • 31
    Digitale Medien
    Digitale Medien
    Theoretical models for electrodialytic sample treatment in trace analysis by liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 460-468 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Electrodialytic sample treatment ; Computer models ; Analyte enrichment
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Basic considerations for analyte enrichment and recovery obtainable by electrodialysis as a sample treatment method are given. Equations are derived which describe the dependence of the concentration profiles of ionic compounds on the electric field strength in a set-up with stagnant donor and acceptor solutions. It is shown that analyte recovery increases when less ion-selective membranes are used in the electrodialysis cell. Computer models are used to estimate the analyte enrichment for a flowing donor (sample) and a stagnant acceptor phase. About 10-fold enrichment can be obtained in an electrodialytic sample treatment system within 20 min under maximum current conditions. A compromise has to be found between analyte recovery and the donor (sample) flow rate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278763
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  • 32
    Digitale Medien
    Digitale Medien
    The lipocalin model for human orosomucoid: Support from the chromatography of orosomucoid-monoclonal antibody complexes (1994)
    Springer
    Chromatographia 39 (1994), S. 475-480 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Orosomucoid ; α1-acid glycoprotein ; Lipocalin ; Monoclonal antibodies
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The accessibility of the surface of human orosomucoid to monoclonal antibodies (MAbs) was investigated by size-exclusion HPLC to examine the validity of its proposed membership in the lipocalin family. The N-terminus half of the molecule contains all the five glycan chains, and of fifty-six MAbs, only one bound to this piece of the polypeptide backbone, indicating that extensive screening was taking place. The simultaneous binding properties of selected MAbs to the fully glycosylated molecule was examined by size exclusion HPLC. The pattern of inhibition was contiguous, with all regions being overlapped. The epitopes of four MAbs having mutual noncompetitive binding were found to be appropriately spaced when placed on a preliminary three dimensional model of orosomucoid. Together, the results support a structure for orosomucoid composed of an exposed continuous protein surface, and a glycan surface screening the remaining protein. Such a structure is provided by the antiparallel β-barrel motif of the lipocalins.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278765
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  • 33
    Digitale Medien
    Digitale Medien
    Simultaneous determination of dexamethasone and betamethasone in pharmaceuticals by reversed-phase HPLC (1994)
    Springer
    Chromatographia 39 (1994), S. 539-542 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Glucocorticoids ; Betamethasone and dexamethasone ; Pharmaceuticals ; Tablet preparations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An HPLC method for the simultaneous determination of the glucocorticoids betamethasone and dexamethasone is described. The method based on the separation of these compounds using a binary watertetrahydrofuran mobile phase and a reversed-phase Hypersil C18 column, was applied to the determination of betamethasone and dexamethasone in tablets.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02268276
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  • 34
    Digitale Medien
    Digitale Medien
    Determination of short chain aliphatic acids in silage effluents by ion exclusion chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 43-51 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Ion exclusion ; Alipathic acids ; Silage effluents
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Short chain aliphatic acids are important components of the dissolved organic matter in silage effluents. Although ion exclusion chromatography offers some advantages for the analysis of these compounds, no attempt has yet been made to prove the suitability of this method for silage effluent analysis. In order to gain experience in this field, the separation characteristics of a Dionex ion exclusion column (IonPac-ICE As5) have been evaluated, the separation conditions have been improved, and several sample clean-up methods have been checked. Ten effluents generated during silaging of five different crops were collected from Bavarian farms and analyzed. Lactic and acetic acids were the predominant aliphatic acids. Pyruvic, formic, propionic, and succinic acid were detected in all samples, whereas glyceric and iso-citric acid were found in a few samples only. If some restrictions of substance specificity and separation efficiency can be accepted, the analytical method presented will be a reliable tool for the analysis of carboxylic acids in silage effluents.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02275725
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  • 35
    Digitale Medien
    Digitale Medien
    Polymer encapsulated packing material for reversed phase liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 756-760 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Polymer encapsulated packings ; Poly(ethylstyrene-divinylbenzene) ; Preparation and evaluation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A series of polymer-encapsulated packing materials for reversed phase high-performance liquid chromatography was prepared by radical polymerization of ethylstyrene and divinylbenzene with vinyl-modified silica in solution. Some characteristics such as polymer structure, swelling propensity, residual silanols, column efficiency and retention properties were evaluated. Such material is easy to pack and yields high column efficiencies. Its superior performance for the separation of mixtures of aromatic hydrocarbons, amino- and hydroxyl group containing compounds are demonstrated by several examples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269632
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  • 36
    Digitale Medien
    Digitale Medien
    Application of β-cyclodextrin for the analysis of estrogenic steroids in human urine by high-performance liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 168-172 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; β-Cyclodextrin in mobile phase ; Estrogens ; Pregnant and non-pregnant women
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A procedure is described for simultaneous determination of estriol, estrone and 17β-estradiol in human urine. After acid hydrolysis of the sulphate conjugates, the estrogens were extracted into diethyl ether. The ether extracts were concentrated and applied directly to an HPLC column. Using a 25 cm C-18 column and acetonitrile-water modified by the addition of β-cyclodextrin as mobile phase, the separation of estriol, estradiol and estrone was achieved within 20 minutes. The extraction of estrogens from the biological matrix is excellent. Estrogens were detected using a UV-detector (280 nm) or a spectrofluorimetric detector (λexc=280nm, λem=312 nm). The latter detection system has been used for the determination of estrogens in the urine of non-pregnant women. The procedure is simple and can be used in clinical practice.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290331
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  • 37
    Digitale Medien
    Digitale Medien
    Convergence of retention for small solutes in reversed-phase liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 158-162 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Reversed-phase chromatography ; Retention mechanism ; Retention convergence ; Small molecules
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary It is shown theoretically that when the concentration of organic solvent in the mobile phase increases, or solute size decreases, log k′ values of small solutes in reversed-phase liquid chromatography (RPLC) will tend to have a minimum value called the convergence point. A theoretical model for evaluating the convergent coordinates of small solutes is presented by using a stoichiometric displacement model for retention (SMDR). The physical meaning of the coordinates of each kind of convergence are also elucidated. The convergence points have either two-dimensional coordinates with a common ordinate (the logarithm of the phase ratio of the column, log φ) or threedimensional corrdinates with two common axes: — log φ and the logarithm of the molar concentration of the pure displacing agent in mobile phase, log aD. The other axis relates to the nature of the solutes, such as carbon number of a homolog, van der Waal's surface area, hydrophobic fragment constant etc. for the latter and those and/or concentration axis for the former. The model was tested with published data and found to give a good fit.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290329
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  • 38
    Digitale Medien
    Digitale Medien
    CP/MAS NMR investigations of silica gel surfaces modified with aminopropylsilane (1994)
    Springer
    Chromatographia 38 (1994), S. 283-290 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chemically bonded phase (CBP) ; Silica-gel with aminopropylsilyl ligands ; Physico-chemical characterization ; CP/MAS NMR investigation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Aminopropyl chemically bonded phases for high performance liquid chromatography (HPLC) have been prepared using mono- and trifunctional methoxyor ethoxysilanes. Three types of silica gel with different surface characteristics were used as support for the chemically bonded phases (CBPs). Surface characteristics of the packings before and after chemical modification were determined by porosity parameters, elemental analysis and CP/MAS NMR spectroscopy.29Si and13C CP/MAS NMR investigations gave informations about different interactions between aminosilyl ligands and/or these ligands and/or water molecules condensed in the pores of the silica gel surface. With decreasing pore diameter of the silica gel the proportion of protonated aminopropyl ligand increases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269769
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  • 39
    Digitale Medien
    Digitale Medien
    The application of ‘Z’-shaped UV cells in open-tubular capillary column liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 313-316 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Open-tubular capillary columns ; ‘Z’-shaped UV cells ; Solvent make-up
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary ‘Z’-shaped UV cells for packed capillary columns cannot be used in open-tubular capillary column liquid chromatography (OT-LC) because of their relatively large volume. With post-column solvent make-up, a commercial ‘Z’-shaped cell (volume 100 nl) was used in our OT-LC system, resulting in 9-fold sensitivity increase against on-column UV detection and with little efficiency loss. A small volume (5 nl) ‘Z’-shaped cell allows the direct coupling of the cell to high efficiency columns. For dilute samples, 9-19-fold sensitivity enhancement could be obtained. However, column efficiency decreases with increasing signal level as a result of peak deformation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269773
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  • 40
    Digitale Medien
    Digitale Medien
    Interconversion of cyclosporin molecular form inducing peak broadening, tailing and splitting during reversed-phase liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 359-364 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Cyclosporin ; Reversible conversion ; Activation energy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Reversed-phase liquid chromatography of cyclosporin A, a peptide immunosuppressant, at various temperatures produced remarkably different chromatograms. At 60°C one sharp peak was obtained, at 23°C this became a single broad peak and between 15° and 0°C this became one high sharp peak followed by a tailing or low plateau. Remarkably different chromatograms were produced also by varying the mobile phase flow-rate. The effects of both temperature and flow-rate on the chromatogram could be accounted for by interconversion between two forms of the cyclosporin molecule. Kinetic analysis showed that one form was converted by first-order kinetics with a half-life of 2.0 min at 20°C and that the apparent activation energy for the conversion was about 18 kcal/mol. The other two immunosuppressants, cyclosporin C and D, were also shown to undergo interconversion. This kinetic analysis of the interconversion should be helpful in clarifying the relationship between molecular structure and activity of the immunosuppressants.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269781
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  • 41
    Digitale Medien
    Digitale Medien
    Determination of carbendazime in lettuce samples by SFE-HPLC (1994)
    Springer
    Chromatographia 38 (1994), S. 395-399 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Supercritical fluid extraction ; Column liquid chromatography ; Carbendazime analysis ; Vegetable samples
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An SFE-HPLC method for the determination of carbendazime in lettuce leaves is described. The method involves a prior lyophilization of the sample and subsequent extraction with supercritical carbon dioxide containing methanol. The extraction conditions are as follows: amount of lyophilized sample, 1 g; CO2 density, 0.75 g/ml; temperature, 50 °C; flow-rate, 1.8 ml/min; dynamic extraction time, 25 min. Carbendazime is determined with an octadecylsilane column, an acetonitrile/water 30∶70 mobile phase and fluorescence detection at 285/317 nm. Carbendazime recoveries from spiked samples were all close to 100%. A comparison with the results from a conventional method for the determination of carbendazime reveals the new method to be more rapid, simple and reproducible for samples with low concentrations of analyte.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269786
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  • 42
    Digitale Medien
    Digitale Medien
    A photometric flow measurements method for characterisation of HPLC pumps (1994)
    Springer
    Chromatographia 38 (1994), S. 421-430 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Pumps ; Flow control
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The measurement of flow constancy and pulsation amplitudes of HPLC pump based on the photoconversion of malachite green leucocyanide is described. The irradiation time and hence the degree of conversion of the leucocyanide is correlated to flow fluctuations of piston driven HPLC pumps. It is possible to measure the amplitude of pulsations and determine the constancy of the flow rate. Most of the pumps show a flow stability better than ±1% measured as relative standard deviation of the flow rate under HPLC conditions (pressure drop 100 bar at 1 ml/min flow rate). The most expensive pump of those tested showed less than ±0.5% flow instability, however, this result was achieved by installation of a large-volume pulsation damper. The method described also allows flow rate measurements under FIA conditions where there is little or no pressure drop at the pump outlet.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269830
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  • 43
    Digitale Medien
    Digitale Medien
    Surface modification by calcium ions—Effect on chromatographic properties of silica (1994)
    Springer
    Chromatographia 39 (1994), S. 29-34 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Calcium modified silica ; Calcium adsorption isotherms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The modification of silica surfaces by calcium ions has been studied by high-performance liquid chromatography. After treatment at pH 7.0 and 9.0 with calcium hydroxide, the modified silicas were characterised by physical and chemical analysis. From measurements by atomic absorption, the amount of calcium adsorbed was 650 ppm on silica modified at pH 7.0, and 4800 ppm on silica modified at pH 9.0. The amount of calcium on the modified silica was 0.574 groups nm−2 at pH 9.0 (original silica: mean pore diameter 176 Å, specific surface 279 m2 g−1, pore volume 1.23 ml g−1, mean particle size 9.8 μm). On the other hand, the amount of calcium in the original silica was 58 ppm. The separation factor, α for N-methylaniline and N,N-dimethylaniline was 5.2 on silica modified at pH 9.0, but could not be measured on silica modified at pH 7.0 and the original silica, using iso-propyl alcohol—n-hexane (0.5∶99.5) eluent.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320454
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  • 44
    Digitale Medien
    Digitale Medien
    Dual injector solvent elution and focussing technique for the on-line analysis of solid-phase extraction cartridges in HPLC (1994)
    Springer
    Chromatographia 39 (1994), S. 45-50 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Sample preconcentration ; Solid-phase extraction ; Solvent focussing ; Injection techniques
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A new dual injector solvent focussing and elution technique developed for high-performance liquid chromatography (HPLC) greatly improves chromatographic efficiency for the on-line analysis of C18 solid-phase extraction (SPE) cartridges. Solutions containing three benzene homologs were used to characterize the dual injector analysis technique and to compare the chromatographic efficiency of this method with conventional SPE analysis methods. Sampling was performed off-line using a glass precolumn cartridge (3 mm i.d. × 30 mm) packed with 15–35 μm C18 silica. On-line cartridge analysis was achieved with two injection valves in either serial or parallel configuration. The injection loop of the first valve contains the eluting solvent, and the cartridge holder is connected in place of the injection loop of the second valve. When an injection is made, both valves are turned to the inject position, and the solvent plug is forced through the cartridge, focussing the analyte at the solvent front as it elutes the cartridge. Solvent focussing at the head of the column, resulting from preconditioning of the column with a small plug of water during injection, further minimizes the variance of the injection plug and improves the chromatographic efficiency. The technique has potential applications to environmental and biological fluid analysis where analyte preconcentration and resolution from the sample matrix components may be difficult with current SPE methods.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320457
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  • 45
    Digitale Medien
    Digitale Medien
    An improved method for the determination of free sphingosine in serum (1994)
    Springer
    Chromatographia 39 (1994), S. 85-90 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Solid phase extraction ; Carbopack B ; Free sphingosine in human plasma
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A rapid, sensitive and selective high-performance liquid chromatographic method has been developed for the determination of sphingosine in human serum. After precipitation with methanol, the samples were extracted using Carbopack B disposable columns; the sphingosine was eluted with 0.05 M hydrochloric acid in methanol-dichloromethane (20∶80, v/v) and the extract evaporated to dryness at 40°C. The sample residue was then reconstituted with methanol and reacted with o-phthaldialdehyde reagent to produce a fluorescent compound. Separation was performed using an LC-18 column with 0.05 M phosphate buffer (pH 7)-methanol-acetonitrile (15∶80∶5, v/v) as mobile phase. Fluorescence detection was performed with excitation and emission wavelengths of 340 and 455 nm, respectively. The serum extract was re-analyzed with a cyano LC column to minimize the possibility of false positive results. The possible interference of compounds having a structure similar to that of sphingosine was evaluated. The mean recovery of sphingosine was 〉94.5%. The limit of detection of the assay was 1 ng mL−1. The between-run and within-run coefficients of variation for replicate analyses were 〈4.0% and 〈3.4%, respectively. The levels of free sphingosine in the serum of 40 normal subjects (20 male and 20 female) was investigated; the average level was 81.6±41.1 ng mL−1 (mean ±S.D.) for males and 85.5±33.7 ng mL−1 for females.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320464
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  • 46
    Digitale Medien
    Digitale Medien
    Analysis of thiamine in dried yeast by high-performance liquid chromatography and high-performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (1994)
    Springer
    Chromatographia 39 (1994), S. 91-96 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Atmospheric pressure chemical ionization-mass spectrometry ; Dried yeast ; Thiamine ; Ion-pair extraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary High-performance liquid chromatography (HPLC) and high-performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (HPLC/APCI-MS) have been applied to the analysis of thiamine in dried yeast. Thiamine was extracted from dried yeast with isobutanol containing sodium 1-octanesulfonate as an ion-pairing agent and determined by HPLC on a reversed phase ODS column with UV detection at 254 nm. Response was linear in the range 25–300 μg/g of thiamine in dried yeast with a coefficient of variation in the reproducibility of 8.0%. Thiamine was recovered in good yield (109.2%, n=5). Identification of the thiamine peak was obtained by the mass spectrum using the HPLC/APCI-MS system. The utility of the selected ion monitoring technique using the HPLC/APCI-MS was also investigated. The results obtained by this method are in good agreement with those obtained by the thiochrome method [1].
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320465
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  • 47
    Digitale Medien
    Digitale Medien
    An improved high-performance liquid chromatographic determination of chlorpropamide in human plasma (1994)
    Springer
    Chromatographia 39 (1994), S. 107-109 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Drug assay ; Chlorpropamide ; Tolbutamide ; Human plasma
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Samples were extracted with dichloromethane and the organic layer evaporated to dryness. The residue was dissolved in methanol, and 10 μl aliquot injected onto the column. Tolbutamide was used as the internal standard for chlorpropamide. The UV detector response was linear over the range 0–200 μg ml−1 with a correlation coefficient of 0.999; detection limit: 0.002 μg ml−1. Within-day and between-day assay variation was generally ≤7%. No interference from endogenous constituents was observed. The utility of the method was demonstrated by determining chlorpropamide in samples from six healthy volunteers following a single oral dose of 250 mg. The procedure is simple and requires small volumes of plasma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320468
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  • 48
    Digitale Medien
    Digitale Medien
    The modiffication of alumina, zirconia, thoria and titania for potential use as HPLC stationary phases through a silanization/hydrosilation reaction scheme (1994)
    Springer
    Chromatographia 39 (1994), S. 649-654 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chemically bonded phases ; Non-silica based supports ; Hydrosilation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A process for bonding a monolayer of silane to the surface of alumina, zirconia, thoria and titania by reaction with the hydrolysis product of triethoxysilane is described. The hydride containing material is then further reacted with a terminal olefin in the presence of a platinum catalyst to produce a chemically modified oxide surface which could be used as a chromatographic stationary phase. The success of this reaction is monitored by diffuse reflectance infrared Fourier transform and cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy as well as by differential scanning calorimetry. On all four oxides both the hydride intermediate and the alkyl bonded product are successfully formed via the silanization/hydrosilation reaction sequence.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274578
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  • 49
    Digitale Medien
    Digitale Medien
    Studies of some experimental conditions for the polymerization of the continuous beds (cross-linked polyacrylamide gels) in order to improve their chromatographic properties (1994)
    Springer
    Chromatographia 39 (1994), S. 655-662 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Continuous beds ; Compressed beds ; Proteins
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Continous chromatographic beds are synthesized by a simple and cost-effective procedure which does not involve the conventional, time-consuming preparation of beads. The aim of this study was to improve the flow properties of the beds by investigating how they are affected by polymerization temperature, the pH of the buffer in which the polymerization takes place, the nature of the constituents of this buffer, the concentrations of catalyst and accelerator and the concentration of the precipitating agent (ammonium sulfate). The infuence of flow rate and the time constants of the detector and recorder on peak width was also studied.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274579
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  • 50
    Digitale Medien
    Digitale Medien
    Reversed phase C18 packings for the separation of polycyclic aromatic hydrocarbons by high performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 668-672 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Monomeric and oligomeric RP packings ; Preparation of RP stationary phases ; Polycyclic aromatic hydrocarbons
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The preparation of C18 stationary phases for the separation of polycyclic aromatic hydrocarbons has been investigated. The effect of the pore size of the silica, the endcapping procedure, the amount of reagent and the amount of water in the preparation was also examined. A good correlation between surface coverage and capacity factor was found. The maximum surface coverage available with our preparation method lies between 3–3.5 μmol m−2, slightly depending on the pore size of the silica. Oligomeric not endcapped C18 packing materials are optimal for the separation of polycyclic aromatic hydrocarbons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274581
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  • 51
    Digitale Medien
    Digitale Medien
    Estimation of phenolic compounds in green pepper berries (Piper nigrum L.) by high-performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 743-746 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Phenolic compounds ; Green pepper berries
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An HPLC method is described for the separation and estimation of phenolic compounds in six commercial varieties of green pepper berries. Among these, two phenolic compounds namely 3,4-dihydroxyphenylethanol glucoside and 3,4-dihydroxy-6-(N-ethyl amino)benzamide that served as efficient substrates for pepper phenolase, showed wide qualitative and quantitative variation in their composition within the varieties. Quantitative estimations of these two compounds were carried out using 4-methylcatechol and epinephrine as external standards. This method is suitable for the estimation of phenolic compounds in green pepper berries in one run.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274592
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  • 52
    Digitale Medien
    Digitale Medien
    Analysis of basic hair dyes by HPLC with on-line post-column photochemical derivatisation (1994)
    Springer
    Chromatographia 39 (1994), S. 138-145 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Diode array detection ; Post-column photochemical derivatisation ; Hair dyes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A reversed phase liquid chromatographic method is proposed for the analysis of basic hair dyes (raw materials and colourant formulations). The performance of the method was enhanced by introducing post-column on-line photochemical derivatisation in combination with a Diode Array Detector. On-line photoderivatisation provided an effective way of selectively transforming the analytes to compounds with different spectral properties. For each analyte two characteristic UV-Visible spectra (photoreactor on and off) were obtained with the same mobile phase and this information in combination with the chromatographic data (k' at pH 3.0 and 4.5) enabled the unambiguous identification of both commonly used, approved, and banned basic hair dyes. Additionally, this approach was found useful to improve the method sensitivity, allowing the determination of analytes present in low concentration (0.03%) in complex commercial formulations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274492
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  • 53
    Digitale Medien
    Digitale Medien
    Control of adsorption and solubility in gradient high performance liquid chromatography. Part 4. Sudden-transition gradient elution of styrene/ethyl methacrylate copolymers in reversed phase mode (1994)
    Springer
    Chromatographia 39 (1994), S. 170-174 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Copoly(styrene/ethyl methacrylate) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Copolymers from styrene and ethyl methacrylate have been separated according to composition byn-heptane gradients on a C18 bonded phase after injection into acetonitrile and subsequent sudden transition to a concentration of either dichloromethane or tetrahydrofuran between 30 and 50% or 20 and 50%, respectively. Acetonitrile is a polar non-solvent for the copolymers under investigation and ensures proper retention of the samples on a non-polar stationary phase. Dichloromethane and tetrahydrofuran are good solvents of moderate polarity. The addition of, e.g., 30 vol% of one of these solvents increased the dissolution power of the starting eluent but not to the extent necessary for elution. The latter was achieved by the addition ofn-heptane, which is a non-solvent for the polymers investigated. Thus, its eluting power must be understood as the consequence of its modifying effect on the polarity of the eluent mixture. The higher the content of copolymer in ethyl methacrylate the earlier it was eluted. Since acetonitrile andn-heptane are only partly miscible, phase diagrams were measured after the addition of either tetrahydrofuran or dichloromethane as a third component. Homogeneous mixtures were obtained on addition of about 30% solvent (one of both of the latter).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274496
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  • 54
    Digitale Medien
    Digitale Medien
    On-line trace enrichment — column liquid chromatography of polar pollutants in surface water using bifunctional membrane-based extraction-disk cartridges (1994)
    Springer
    Chromatographia 39 (1994), S. 239-245 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Membrane-extraction disks ; On-line trace enrichment ; Polar pollutants ; Surface water
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An on-line trace-enrichment system, using a bifunctional membrane extraction-disk cartridge, has been combined with a column liquid chromatography separation for the simultaneous determination of basic, neutral and acidic pollutants in surface water. The enrichment device consisted of a specially constructed holder containing both C-18 and cation-exchange disks. The holder can contain up to 25 disks of 0.5 mm thickness and 4.6 mm diameter. Before trace enrichment of 20 ml of surface water (pH 3.0), calcium ions were removed from the sample by means of an oxalic acid precipitation. Desorption of the cartridge was at elevated temperature using reversed-phase gradient elution; detection was performed with a diode-array UV absorbance detector. The detection limits for the test compounds in surface water are typically 0.5–2 μg/l; the calibration graphs are linear from the lower limit of determination up to 50 μg/l.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274506
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  • 55
    Digitale Medien
    Digitale Medien
    Retention characteristics of fluorinated bonded silica phase in reversed-phase liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 285-293 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Fluorinated chemically bonded silica ; Aromatic compounds ; Molecular shape vs. retention
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Fluorinated bonded silica has been evaluated as a packing material in reversed-phase liquid chromatography (RPLC) with polycyclic aromatic hydrocarbons, chlorinated benzenes and substituted benzenes as sample probes. The bonded material is useful as a reversed-phase stationary phase and for polar compounds it offers a specific selectivity not found with octadecylsilica (ODS) phases. The phase also retains non-planar compounds more than planar molecules. The results can be explained by conformational differences between ODS and the fluorinated bonded phase by MM2 calculation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274515
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  • 56
    Digitale Medien
    Digitale Medien
    Optimization of mobile phases for HPLC of cis-trans carotene isomers (1994)
    Springer
    Chromatographia 39 (1994), S. 346-354 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; α-Carotene cis-isomers ; β-Carotene cis-isomers ; Polymer stationary phase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Various methanol-based, binary and ternary solvent systems were compared with respect to resolution of cis isomers of α and β-carotene by reversed-phase HPLC. A ternary system: acetonitrile-methanol-methylene chloride (75∶15∶10), or a binary system: acetonitrilemethanol (90∶10 or 5∶95) provided the best separation of β-carotene and its four cis isomers, 9-cis, 13-cis, 15-cis and 13,15-di-cis-β-carotene. The elution order of 9-cis and 13-cis-β-carotene was dependent on the methanol concentration. Methanol-methylene chloride (99∶1) resolved α-carotene and its three cis isomers, 9-cis, 13-cis, and 15-cis-α-carotene. It also proved the best for simultaneous separation of cis isomers of α and β-carotene. Sample solvent can affect the separation efficiency of each isomer. The presence of cis isomers of α and β-carotene in fresh and cooked carrots was also determined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274524
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  • 57
    Digitale Medien
    Digitale Medien
    Chromatographic determination of D-amino acids as native constituents of vegetables and fruits (1994)
    Springer
    Chromatographia 39 (1994), S. 419-426 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Gas chromatography ; Chirasil-Val ; Amino acid enantiomers ; N-Isobutyryl-cysteine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Free D-amino acids (D-AA) were detected as native constituents in juices of vegetables (cultivars of cabbage, tomato, carrot, garlic) and fruits (organes, clementine, grapefruit, lemon, apples, pear, grapes) using gas chromatography (GC) or high-performance liquid chromatography (LC). For investigation by GC, AA enantiomers were converted into theirN(O)-pentafluoropropionyl 2-propyl esters and resolved on a Chirasil-L-Val capillary column. For determination by LC, precolumn derivatization of AA enantiomers usingo-phthaldialdehyde together with the chiral thiolsN-isobutyryl-L-cysteine orN-isobutyryl-D-cysteine and fluorescence detection of the diastereomeric isoindole derivatives, resolvable on an octadecylsilyl stationary phase, were used. D-Ala (0.6–3.8%) was detected in all freshly pressed plant juices usually in the highest relative amounts. Other D-AA detected were D-Asx (0.1–1.9%), D-Glx (0–1.3%), D-Ser (0–1.7%), D-Arg (0.4–1.2%, in grapes, orange, grapefruit, and clementine) and D-Leu and D-Val (1% in cabbage). Absolute amounts of native D-AA were totally 28–57 μmol L−1 in fruit juices, 14.5 μmol L−1 in a tomato juice and 8.5 μmol L−1 in a carrot juice.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278756
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  • 58
    Digitale Medien
    Digitale Medien
    Temperature effect in separation of fullerene by high-performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 453-459 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Fullerenes ; Octadecylsilicas ; Temperature effect
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The effect of column temperature, especially at low temperatures, on the separation of fullerenes on monomeric and polymeric octadecyl silica (ODS) bonded phases has been studied. Decreasing the column temperature induces an increase in selectivity. The best temperature for the separation of fullerenes was determined for both types of ODS phase with n-hexane eluent. The selectivity for higher fullerenes on monomeric phases becomes similar to that on polymeric phases to low temperature. It has been found that as the carbon content of monomeric phases is increased, the selectivity also becomes similar to polymeric phases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278762
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  • 59
    Digitale Medien
    Digitale Medien
    A chromatographic and chemometric study of the bark phenolic compounds of two poplar clones with different resistance toDiscosporium populeum (1994)
    Springer
    Chromatographia 39 (1994), S. 481-489 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Phenolic compounds ; Poplar bark ; Discosporium populeum infection ; Chemometric data evaluation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Reversed-phase high performance liquid chromatography with diode array detection was used to analyze phenolic compounds contained in bark extracts of two different poplar clones known to have different resistance toDiscosporium populeum infection. Statistical treatments both monovariate and multivariate were applied to the results in order to identify regularities useful to discriminate the polar resistance and to check the importance of seasonal and cultivation site related factors. For the two clones examined phenolic compounds showed great discrimination ability not influenced by either sample collection period or cultivation site.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278766
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  • 60
    Digitale Medien
    Digitale Medien
    Determination of catecholamines in urine by micellar liquid chromatography with coulometric detection (1994)
    Springer
    Chromatographia 39 (1994), S. 591-596 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Micellar liquid chromatography ; Catecholamines in urine ; Coulometric detection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The determination of catecholamines by HPLC with a sodium dodecyl-sulphate (SDS), micellar mobile phase on a C18 column and with coulometric detection was studied. The eluate was conditioned at +0.25 and +0.00 V, and the current at −0.16V was recorded. A previously developed model which describes the chromatographic behaviour of solutes in HPLC with hybrid, micellar mobile phases was used to optimize the SDS and ethanol concentrations. A mobile phase of 0.15M SDS in a phosphate buffer of pH 3.4 and without ethanol is recommended. The limits of detection were 0.4–0.7 ng ml−1. The procedure was applied to the determination of unconjugated L-dopa, norepinephrine and dopamine in urine. Direct injection of the urine samples gave high results but the unconjugated catecholamines could be determined with a single solid-phase extraction step on an alumina column.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02268285
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  • 61
    Digitale Medien
    Digitale Medien
    Improved separation of diastereoisomers in capillary electrophoresis using a mixture of β-cyclodextrin and sodium taurodeoxycholate (1994)
    Springer
    Chromatographia 39 (1994), S. 627-630 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Micellar electrokinetic capillary electrophoresis ; Tetrahydrocarbazole derivatives ; β-Cyclodextrin ; Taurodeoxycholate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary 2,3,4,6-tetra-O-acetyl-β-D-glucopranosyl isothiocyanate derivatives of a number of basic compounds, containing one chiral center, have been prepared. The indirect resolution of enantiomers was achieved with a high separation efficiency by capillary electrophoresis, using a sodium taurodeoxycholate/β-cyclodextrin system. This methodology was found to be superior to the resolution of the same derivatives by reversed phase HPLC analysis. A possible mechanism for stereoselectivity is described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02268292
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  • 62
    Digitale Medien
    Digitale Medien
    Chemistry and micromorphology of compound epicuticular wax crystalloids (Strelitzia type) (1994)
    Springer
    Plant systematics and evolution 193 (1994), S. 115-123 
    Details
    ISSN: 1615-6110
    Schlagwort(e): Angiosperms ; Strelitzia ; Heliconia ; Typha ; Benincasa ; Epicuticular wax ; wax ultrastructure ; wax chemistry ; systematics ; taxonomy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Certain non-liliiflorous taxa within the monocotyledons (e.g.,Strelitzia, Heliconia, Typha) are characterized by compound epicuticular wax rodlets (Strelitzia type). Similar rodlets are also encountered on the surface of the dicotyledonous plantBenincasa hispida (Thunb.)Cogn. Chemical analysis of the surface wax from both sources showed that the rodlets are chemically distinct. The rodlets of the monocotyledons consist exclusively of aliphatic wax lipids, mainly wax esters. In contrast, the rodlets ofBenincasa are cheifly composed of triterpenol acetates and triterpenols. Formation of rodlets is therefore interpreted as ultrastructural convergency. It is concluded that taxonomical studies on wax crystalloids can be misleading when interpreted in terms of micromorphology of crystalloids only.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00983545
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  • 63
    Digitale Medien
    Digitale Medien
    Floral structure and evolution of primitive angiosperms: Recent advances (1994)
    Springer
    Plant systematics and evolution 192 (1994), S. 79-97 
    Details
    ISSN: 1615-6110
    Schlagwort(e): Angiosperms ; paleoherbs ; Magnoliidae ; Gnetales ; Floral evolution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Concepts of primitive angiosperm flowers have changed in recent years due to new studies on relic archaic groups, new paleobotanical finds and the addition of molecular biological techniques to the study of angiosperm systematics and evolution.Magnoliidae are still the hot group, but emphasis is now on small primitive flowers with few organs and also on the great lability of organ number. Of the extant groups, a potential basal position of the paleoherbs has been discussed by some authors. Although some paleoherbs have a simple gynoecium with a single orthotropous ovule, anatropous ovules may still be seen as plesiomorphic in angiosperms. Anatropy is not necessarily a consequence of the advent of closed carpels. It may also exhibit biological advantages under other circumstances as is the case in podocarps among gymnosperms. Valvate anthers have now been found in most larger subgroups of theMagnoliidae (recently also in paleoherbs) and in some Cretaceous fossils. Nevertheless, as seen from its systematic distribution, valvate dehiscence is not necessarily plesiomorphic for the angiosperms, but may be a facultative by-product of the thick connectives and comparatively undifferentiated anther shape inMagnoliidae and lowerHamamelididae. A perianth is relatively simple in extantMagnoliidae or even wanting in some families. In groups with naked flowers the perianth may have been easily lost because integration in the floral architecture was less pronounced than in more advanced angiosperm groups. Problems with the comparison of paleoherb flowers with those ofGnetales are discussed. The rapid growth of information from paleobotany and molecular systematics requires an especially open attitude towards the evaluation of various hypotheses on early flower evolution in the coming years.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00985910
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  • 64
    Digitale Medien
    Digitale Medien
    The characterisation and identification of a naturally occurring hybrid in the genusLeucaena (Leguminosae: Mimosoideae) (1994)
    Springer
    Plant systematics and evolution 192 (1994), S. 177-197 
    Details
    ISSN: 1615-6110
    Schlagwort(e): Angiosperms ; Leguminosae ; Leucaena esculenta ; L. leucocephala ; Hybridization ; sterile triploid ; morphometric analysis ; DNA characters ; restriction site analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Phytogeographical, morphological, and molecular evidence for the widespread but sporadic occurrence of sterile hybrids betweenLeucaena leucocephala subsp.glabrata andL. esculenta subsp.esculenta in South-Central Mexico is presented. Most morphological and DNA characters studied in the putative hybrids showed states intermediate between the proposed parental taxa. The occurrence of non-additive nuclear ribosomal DNA phenotypes is discussed and the need to use a suite of nuclear taxon-specific markers to determine hybridity is emphasized. The origin of the hybrid is discussed in relation to the disruption of the distributions of both parental taxa through use by man as minor food plants, providing another example of the important influence of human interference on the evolution ofLeucaena. The successful use of dried leaf material as a source of DNA is highlighted as an efficient way to identify sterile hybrids at the molecular level.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00986251
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  • 65
    Digitale Medien
    Digitale Medien
    Chromatography of esculin from stems and bark ofAesculus hippocastanum L. for consecutive vegetative periods (1994)
    Springer
    Chromatographia 38 (1994), S. 766-770 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Thin-layer chromatography ; Densitometry ; Spectrophotometry of extracts ; Esculin, fraxin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Coumarin glucosides, esculin and fraxin, were determined in several older and younger layers of stems ofAesculus hippocastanum L. by three methods (TLC-densitometry, TLC-extraction and spectrophotometric determinations, HPLC) during the vegetative period (May–October). Variation of their content during these months is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269634
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  • 66
    Digitale Medien
    Digitale Medien
    Efficiency of porous hydrophilic polymer-based packing materials in chromatographic analysis of drugs existing with polypeptide (1994)
    Springer
    Chromatographia 38 (1994), S. 177-182 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Hydrophilic polymer-based packing material ; Direct injection of serum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A size monodispersed restricted-access polymeric packing material has been prepared through a simple and easy one-step method of co-polymerization of glycerol monomethacrylate and glycerol dimethacrylate with cyclohexanol as prorogen. A typical seeded polymerization (two step swelling and polymerization method) in an aqueous medium gave a 90 % yield of porous beads which could be utilized as a packing material in high performance liquid chromatography (HPLC) without any size classification due to the excellent size monodispersity. A BET measurement and size exclusion chromatography in either tetrahydrofuran or water revealed that the prepared material had only small pores (around 100 Å in diameter). It showed ample hydrophobicity for the separation of hydrophilic drug molecules in 10% aqueous acetonitrile buffer, while polypeptides such as bovine serum albumin were excluded and eluted before the void volume of the column with quantitative recovery.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290333
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  • 67
    Digitale Medien
    Digitale Medien
    Lipid class analysis by normal phase high performance liquid chromatography, development and optimization using multivariate methods (1994)
    Springer
    Chromatographia 38 (1994), S. 317-324 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Lipid class analysis ; Experimental design and optimization ; Chemometrics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A general method for the analysis of lipid classes by liquid chromatography has been developed using a multivariate optimization strategy to target optimal system conditions. The method was validated using a ruggedness test in the form of a Plackett-Burman design thereby exploring the immediate region around the optimum to ensure stable analytical conditions. Detection and quantitation were optimized by a factorial design in the light scattering detector parameters thus ensuring maximum detector response. This method was found to be suitable for a broad range of lipid sources from vegetable and animal origin, examples of the separation achieved are given for oat kernel, soybean and bovine milk lipids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269774
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  • 68
    Digitale Medien
    Digitale Medien
    Solute-micelle association constants of some polynuclear aromatic hydrocarbons by micellar liquid chromatography with alcohol additives to mobile phase (1994)
    Springer
    Chromatographia 38 (1994), S. 342-348 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Hybrid mobile phases containing alcohols ; Solute-micelle association constants ; Polynuclear aromatic hydrocarbons
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The interaction between some polynuclear aromatic hydrocarbons of environmental concern, and sodium dodecylsulphate and hexadecyltrimethylammonium bromide in the presence of methanol, 2-propanol and n-butanol has been evaluated by high-performance liquid chromatography using micellar mobile phases. Solute-micelle association constants have been determined for the compounds investigated. The results show that the addition of the alcohol to the mobile phase decreases the association constant values, methanol 〈2-propanol 〈n-butanol, relative to those in the absence of any additive.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269778
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  • 69
    Digitale Medien
    Digitale Medien
    Determination of catecholamines as aminochromes by micellar liquid chromatography with thermal lens spectrophotometric detection (1994)
    Springer
    Chromatographia 38 (1994), S. 365-372 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Micellar liquid chromatography ; Determination of catecholamines ; Aminochromes ; Thermal lens spectrometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The determination of catecholamines (CAs) using micellar liquid chromatography with thermal lens spectrophotometric detection has been studied. CAs are oxidized with hexacyanoferrate(III) to aminochromes which are separated with a mobile phase of 0.05 M sodium dodecyl sulphate, 7% propanol and 0.03 M citrate buffer, pH 4.8, on a partially endcapped C18 column. The aminochrome-micelles and aminochrome-stationary phase association constants are evaluated. Using the 488 nm line of an Ar+ laser with 250 mW pump power the limits of detection are about 4 ng mL−1. The technique is applied to the determination of unconjugated CAs in urine using isoproterenol as internal standard.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269782
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  • 70
    Digitale Medien
    Digitale Medien
    Liquid chromatography of cyclodextrins with indirect photometric detection of phenolphthalein inclusion complexes (1994)
    Springer
    Chromatographia 38 (1994), S. 453-455 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Cyclodextrins ; Inclusion complexation ; Indirect photometric detection ; Octadecyl-bonded poly(vinylalcohol) packings
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary β- and γ-cyclodextrin (CD) separated by liquid chromatography have been indirectly detected by depression of the background absorbance at a visible wavelength by means of inclusion complexation with phenolphthalein. The background signal was generated by phenolphthalein in an alkaline medium. Octadecyl-bonded poly(vinylalcohol) packings were employed as the stationary phase, which allowed the use of alkaline mobile phases, and eliminated post column mixing of reagents. The detection limits for β- and γ-CD were 0.1–0.5 μM at a signal to noise ratio of 3. α-CD could not be measured by the present detection principle.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269835
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  • 71
    Digitale Medien
    Digitale Medien
    Comparative study of solid-phase extraction of phenolic compounds. Influence of the ion pair reagent (1994)
    Springer
    Chromatographia 38 (1994), S. 579-584 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Phenolic compounds ; Ion-pair solid-phase extraction ; Comparison of sorbents
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A comparative study of the solid phase extraction of phenolic compounds in water was carried out. Three different sorbents, C18, CH and PLRP-S, were tested for the preconcentration process in order to determine phenolic compounds in water at μg l−1 levels by reversed-phase LC separation and diode-array detection. The addition of an ion-pair reagent in the extraction process was also studied in order to increase the breakthrough volume of some compounds. Using the optimized conditions the limit of detection was less than 0.5 μg l−1, the maximum admissible concentration (MAC) in drinking water. The method was applied to determine phenolic compounds in Ebro river water however no phenols were found within the detection limits of the method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02277157
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  • 72
    Digitale Medien
    Digitale Medien
    Extraction of basic drugs from whole blood and determination by high performance liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 617-623 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Extraction-determination ; Basic drugs ; Blood
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A new method for the extraction of basic drugs from whole blood based on the use of a buffered protein precipitating reagent at pH9, to form NiWO4 in biological fluids and a ternary organic extracting phase of density below 1 is proposed. The extract is analysed by high performance liquid chromatography using a Hypersil C8 column and detection at 230 nm; the mobile phases used consist of binary mixtures of acetonitrile and aqueous solutions containing 20 mmol/l ofn-propylamine at pH 5 andn-hexylamine at pH 4, as blockers of the free silanol groups. The proposed method was applied to the determination of 16 basic drugs including narcotics, analgesics, cocaine-related compounds and adulterants, as well as 8 benzodiazepines, in whole blood.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02277164
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  • 73
    Digitale Medien
    Digitale Medien
    Determination of imazethapyr and imazapyr residues in soil by coupled-column liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 62-66 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Column switching ; Imidazolinone herbicides in soil ; Imazethapyr ; Imazapyr
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A column-switching method using two separation columns combined with UV detection at 260 or 236 nm has been used to determine the imidazolinone herbicides imazethapyr and imazapyr in soils. The residues were extracted from the soil with 0.1 M aqueous sodium carbonate solution and, after adjusting the pH to 2.0, the solution was partitioned with dichloromethane. Limits of determination for imazethapyr and imazapyr were 3 μg/kg. Recoveries were from 55 to 75% for both imidazolinone herbicides in the range 3–100 μg/kg in soil.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320459
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  • 74
    Digitale Medien
    Digitale Medien
    Kinetic performance of open-tubular and packed columns in LC using the same stationary phase: Immobilized polymethyloctadecylsiloxane (1994)
    Springer
    Chromatographia 39 (1994), S. 729-739 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Polymeric stationary phase coatings ; PMSC18 ; Column evaluation ; Peak capacity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary For the first time a direct comparison of the kinetic performance of narrow-bore (5–15 μm I.D.) opentubular columns (OTCs) and conventional packed columns in LC was carried out with stationary and mobile phases with identical chemical composition. The polymeric stationary phase was a polymethyloctadecylsiloxane (PMSC18) and the columns were evaluated in reversed-phase LC. In the open-tubular columns oncolumn detection was performed with laser-induced fluorescence. The observed column performance is presented in various ways, to take account of the basic differences of OTCs and packed columns. Experimental data was compared with theoretical models by use of a curve fitting procedure. The static coating method generates OTCs that perform close to theoretical predictions, and the packed columns were outperformed by the OTCs with regard to efficiency. A 6 m long and 6.3 μm I.D. OTC showed a minimum reduced plate height, hmin. of 0.5 at k′=0.27, which equals 1 900 000 theoretical plates. Also, it was established that the open-tubular columns provide higher resolution in a given analysis time. However, the importance of sufficient retention in OTCs is once again substantiated. Peak capacity plots illustrate that the k′ “window” should be optimized in order to reach maximum resolution (k′ 0–2 for OTCs and 0–5 for packed columns).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274590
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  • 75
    Digitale Medien
    Digitale Medien
    Chromatographic characterization of a hexapeptide containing three thiol groups, intrinsic to the metallothionein structure (1994)
    Springer
    Chromatographia 39 (1994), S. 146-154 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Peptide characterization ; Thiol groups ; Electrochemical detection ; Metallothionein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The hexapeptide Lys-Cys-Thr-Cys-Cys-Ala [56–61] MT I is a molecule intrinsic to the metallothionein structure. Its chromatographic behaviour on a reversed-phase column, using electrochemical detection has been studied in order to get a better understanding of its chemical stability under various conditions. The chromatogram of the peptide consists of two peaks. The optimization procedure for their separation is presented and a hydrodynamic voltammogram has been generated. The relative proportion of the two peaks can vary with experimental conditions and is clearly dependent of the peptide concentration. Following the various experiments to which the peptide was submitted, namely elution after air oxidation, under inert atmosphere, in basic pH, after addition of an oxidizing agent (H2O2) and after addition of a reducing agent (2-mercaptoethanol), a reaction scheme was suggested: transformations of the reduced hexapeptide (three free thiol groups) into—as a first step—its intramolecular oxidized form (one SS bond, one free SH) and then into—as a second step—the fully oxidized dimeric form (no more free SH). Electrochemical detection allows a quantitative follow-up of the thiol oxidation and hence, of the disappearance of the reduced peptide.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274493
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  • 76
    Digitale Medien
    Digitale Medien
    Luminarin 9: A new fluorescent reagent for the precolumn derivatizatioin of main volatile and non-volatile N-nitrosamines in RP-HPLC (1994)
    Springer
    Chromatographia 39 (1994), S. 185-191 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; N-nitrosamines ; Fluorescent derivatives ; Luminarin 9 ; Precolumn derivatization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A sensitive precolumn fluorescence derivatization method for low level detection of the, volatile (N-nitrosodimethylamine and N-nitrosopyrrolidine) and non-volatile N-nitrosamines (N-nitrosoproline and N-nitrosodiethanolamine) an high-performance liquid chromatography was developed. This method is based on the denitrosation of the compounds of interest by a mixture of hydrobromic acid and acetic acid to produce the corresponding secondary amines. These are, then, able to react with, a quinolizinocoumarin derivative (luminarin 9®) to form highly fluorescent labelled N-nitrosamine derivatives. The structural elucidation of the luminarin 9® derivatives of N-nitrosoproline and N-nitrosodimethylamine by way of example, were established by liquid chromatography-mass spectrometry (LC-MS) and by direct chemical ionization-mass spectrometry (CI-MS). The separation, derivatization and detection conditioins were optimized for all the studied compounds. The detection limits (signal to noise ratio=3) were between 0.4 and 1.0 pmol injected depending on the compound. The calibration graphs were linear for derivatized amounts in the range of 0.5–40 nmol for N-nitrosodimethylamine and N-nitrosopyrrolidine, 0.4–2- nmol for N-nitrosoproline and 1.0–40 nmol for N-nitrosodiethanolamine. The repeatability (RSD less than 3.5%, n=6) and reproducibility (RSD less than 4.8%, n-6) were satisfactory.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274499
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  • 77
    Digitale Medien
    Digitale Medien
    Computerized optimization of gradient elution conditions with ternary solvent mobile phases in RPLC (1994)
    Springer
    Chromatographia 39 (1994), S. 216-223 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Gradient elution ; Optimization of gradients ; Ternary solvent mobile phase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary In this work, an optimization procedure for gradient RPLC separation, using ternary mobile phases, is described. This procedure requires eight preliminary experiments in gradient elution mode to predict the retention surface for each solute over the whole triangular space. This is followed by computerized calculations to determine the best ternary gradient elution profile with respect to both selectivity and analysis time. The efficiency of this procedure from the point of view of rapidity and of accuracy, is illustrated for the specific separation of twelve phenyl urea herbicides.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274503
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  • 78
    Digitale Medien
    Digitale Medien
    Determination of tacrolimus (FK 506) in whole blood using liquid chromatography and fluorescence detection (1994)
    Springer
    Chromatographia 39 (1994), S. 490-496 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Precolumn derivatization ; Dansylhydrazine ; Fluorescence detection ; Tacrolimus (FK 506) in blood
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A sensitive and selective liquid chromatographic method, using precolumn derivatization with dansylhydrazine followed by fluorescence detection, has been developed for the determination of tacrolimus (FK 506) in whole blood. After haemolysis, whole blood samples are extracted with diethyl ether and derivatized. After on-line removal of excess dansylhydrazine on a C18 precolumn, the derivative is loaded on to a C18 clean-up column, and a heart cut is subsequently transferred to a graphitized carbon column, where the final separation takes place. The method requires 1 ml of sample and has a limit of quantitation of 3 ng/ml. At the 15 ng/ml level the precision isca 10%, and the response is linear from the limit of quantitation toca 200 ng/ml of FK 506 in whole blood. The capacity of the method is 50 samples/day and about 1000 1-ml samples can be analyzed without changing either clean-up or separation column. Finally, the applicability of the method for therapeutic drug monitoring is shown.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278767
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  • 79
    Digitale Medien
    Digitale Medien
    Spectroscopic studies of butylphenyl, mono-ol and perfluorinated bonded phases (1994)
    Springer
    Chromatographia 39 (1994), S. 520-528 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; New bonded phases ; 13C and29Si CP-MAS NMR ; DRIFT ; ESCA
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A variety of olefins were bonded to silaceous supports through a hydride modified substrate. The products were then examined by13C and29Si solid state-NMR with cross-polarization (CP) and magic angle spinning (MAS). Information about the surface was also obtained by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and the related photoelectron spectroscopic technique (ESCA). Carbon analysis on bonded silicas was carried out and surface coverage was calculated. Confirmation of the organic groups bound to the silica support was possible. The hydride intermediate is shown to be a versatile material for bonding a wide variety of organic moieties to silica surfaces.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02268274
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  • 80
    Digitale Medien
    Digitale Medien
    Analysis of isomers of cholesteryl acetate hydroperoxides by HPLC and GC-ITDMS (1994)
    Springer
    Chromatographia 39 (1994), S. 577-580 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography-mass spectrometry ; Column liquid chromatography ; Cholesteryl acetate ; Hydroperoxide formation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Gas chromatographic, high performance liquid chromatographic and GC-ion trap detector mass spectrometric analyses of the hydroperoxides formed during thermal peroxidation of cholesteryl acetate, are reported and discussed. The hydroperoxides were separated from the thermal-oxidised mixture by solid-phase extraction, fractionated and individually collected by HPLC. Each hydroperoxide was then chemically reduced with NaBH4 to a hydroxy-derivative. The GC and MS characteristics of hydroxy- and TMS-derivatives were compared against available standards. Only 7β-hydroperoxide and 7α-hydro-peroxide of cholesteryl acetate were found, as reported in the literature for cholesterol.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02268282
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  • 81
    Digitale Medien
    Digitale Medien
    Retention behavior of aromatic hydrocarbons in reversed-phase liquid chromatography with ion-exchange-induced stationary phases (1994)
    Springer
    Chromatographia 39 (1994), S. 597-601 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Ion-exchange-induced stationary phase ; Retention behavior ; Aromatic hydrocarbons
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The retention behavior of aromatic hydrocarbons on anion-exchangers modified with alkylsulfate or alkanesulfonate has been examined by column liquid chromatography. Several parameters affected the retention of analytes, involving concentration of the modifier in the mobile phase, its alkyl chain length and mobile phase composition. Stationary phases modified with a reagent having longer alkyl chains achieved better column efficiency. The separation factor achieved on ion-exchange-induced stationary phases foro-terphenyl and triphenylene was larger than that on alkyl-bonded silica gel.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02268286
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  • 82
    Digitale Medien
    Digitale Medien
    Gynoecium and perianth inZanthoxylum s.l. (Rutaceae) (1994)
    Springer
    Plant systematics and evolution 189 (1994), S. 165-191 
    Details
    ISSN: 1615-6110
    Schlagwort(e): Angiosperms ; Rutaceae ; Zanthoxylum ; Fagara ; Flower morphology ; perianth ; gynoecium ; acrostylous and anacrostylous-basistylous carpels ; compitum ; taxonomy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The question whether the uniseriate perianth ofZanthoxylum L. s. str. is homologous with the calyx or the corolla of taxa included inFagara, or of an independent origin, has been controversial for a long time, but the arguments mostly have remained theoretical. The present investigation of floral structures indicates that there are two different types of uniseriate perianth inZanthoxylum s. str. Therefore, this taxon does not represent a natural group and should be united withFagara asZanthoxylum s.l. The infrageneric taxonomy of this genus is still very ambiguous. It is shown that differences in indumentum, number of sepals and petals (5-4-3) resp. perianth segments (4–9), stamens (3–6), and free carpels (1–5) are of systematic relevance. Particularly important but so far neglected is carpel shape, where an acrostylous and an anacrostylous-basistylous type can be recognized. Stigmata of 2 or more carpels mostly fuse to form a compitum. 4–5-merous flowers with calyx and corolla, and acrostylous carpels are considered as plesiomorphic character states in the genus. On the basis of ± corresponding morphological and phytochemical progressions a working hypothesis about the relationships withinZanthoxylum s.l. is presented in graphical form (Fig. 9).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00939724
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  • 83
    Digitale Medien
    Digitale Medien
    cpDNA intergene sequences corroborate restriction site data for reconstructingRubiaceae phylogeny (1994)
    Springer
    Plant systematics and evolution 190 (1994), S. 245-248 
    Details
    ISSN: 1615-6110
    Schlagwort(e): Angiosperms ; Rubiaceae ; Chloroplast DNA ; atpB-rbcL intergene region ; phylogeny
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Representatives of seven genera from five tribes ofRubiaceae have been compared in respect to a non-coding intergene cpDNA region of about 1000 bp, situated between the atpB and the rbcL genes. The resulting most parsimonious PAUP cladogram corresponds very well with one based on total cpDNA restriction site data obtained byBremer & Jansen (1991). The two different molecular analyses thus corroborate each other and contribute to an improved systematic arrangement of the large family, e.g., in respect to placing the tribeHedyotideae clearly into the subfamilyRubioideae, closer toRubieae than toPsychotrieae.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00986196
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  • 84
    Digitale Medien
    Digitale Medien
    Merosity in flowers: Definition, origin, and taxonomic significance (1994)
    Springer
    Plant systematics and evolution 191 (1994), S. 83-104 
    Details
    ISSN: 1615-6110
    Schlagwort(e): Angiosperms ; androecium ; Merosity ; phyllotaxis ; pseudowhorl ; zygomorphy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The term merosity stands for the number of parts within whorls of floral organs, leaves, or stems. Trimery is considered to be a basic condition that arose through the cyclisation of a spiral flower. Pentamery is mostly derived from trimery by the repetitive fusion of two different whorls. Dimery is either directly derived from trimery, or through pentamery as an intermediate stage. Tetramery is linked with pentamery and should not be confused with dimery. Possible causes for a change in merosity are the reduction of the number of carpels and zygomorphy in flowers. Derivations of different merosities have important consequences for the arrangement of the androecium (the insertion of stamen whorls, their identifications, and their number). It is concluded that two main groups can be identified within the angiosperms: magnolialean and monocotyledonean taxa are mostly trimerous or dimerous; non-magnolialean dicots are mostly pentamerous or tetramerous.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00985344
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  • 85
    Digitale Medien
    Digitale Medien
    Determination of sugars by liquid chromatography with post-column catalytic derivatization and fluorescence detection (1994)
    Springer
    Chromatographia 38 (1994), S. 12-16 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Carbohydrates ; Post-column fluorescence derivatization ; Post column catalytic reaction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A method for the determination of reducing sugars such as fructose and glucose and nonreducing sugar such as sucrose by high performance liquid chromatography followed by an acidic hydrolysis and a derivatization with benzamidine has been developed. After separation of sugars on a gel column packed with a polymer-based cation exchange material (Sugar-Pak I, Waters-Millipore), the sucrose is first hydrolysed in a solid phase reactor to convert it into reducing subunits. A post-column fluorigenic reaction with benzamidine under alkaline condition allows the selective determination of both natural and converted reducing carbohydrates. This procedure has proven to be selective (fluorigenic detection) and highly sensitive (allowing detection as little as picomoles amounts), reproducible and linear over a broad range of concentrations: 5×10−4 to 1.0×10−2 M. The applicability of this method to natural matrices such as plant extracts and beverages is also described. The sugar content of a barley extract has been determined and compared with a specific enzymatic test. The determined sugar content of natural and commercial lemon juices as well as of Cola beverages has been compared with those found by the conventional LC refractive index analytical procedure. In all cases, the results were comparable and were within the experimental errors of the methods.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02275720
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  • 86
    Digitale Medien
    Digitale Medien
    Capillary electrophoresis as an alternative to HPLC for determination of honey flavonoids (1994)
    Springer
    Chromatographia 38 (1994), S. 71-78 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Micellar electrokinetic capillary chromatography ; Column liquid chromatography ; Honey flavonoids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The general objective is to provide an alternative methodology based on capillary electrophoresis (CE) to characterize flavonoids from honey and hence determine its botanical origin. The specific objective is to compare the separation of flavonoids by CE with those achieved by HPLC to assess CE as an alternative technique for the determination of honey flavonoids. Fourteen different flavonoids isolated from honey were analysed by MECC and compared to the HPLC separations. It was difficult to find specific experimental conditions to separate all the flavonoids from honey in a single MEKC run. Three chromatographic conditions are optimized and, depending on the flavonoid markers sought in honey, the appropriate detection method should be chosen. Compared to the HPLC results, it is clear that CE could be an alternative technique in honey flavonoids analysis and particularly in the study of its geographical and floral origin.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02275729
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  • 87
    Digitale Medien
    Digitale Medien
    Determination of triamterene in urine by HPLC using fluorescence detection and column-switching (1994)
    Springer
    Chromatographia 38 (1994), S. 29-34 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Column-switching ; Determination of triamterene ; Fluorescence detection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A liquid chromatographic method incorporating column-switching and fluorimetric detection for the determination of triamterene in untreated urine, is described. The urine samples (5 μL) were directly introduced onto an Hypersil ODS-C18, 30 μm (20 mm×2.1 mm I.D.) pre-column. Polar urinary compounds were removed by flushing the pre-column with water for 1 min, and the analyte was then switched onto an HP-LiChrospher RP C18,5 μm (125 mm×4mm ID) analytical column using an acetonitrile/phosphate buffer gradient elution. Fluorescence detection was performed at 230 nm excitation and 430 nm emission wavelengths. The recovery of drug was 102±2% in the 0.10–20.0 μg/mL concentration range, the limit of detection being 5 ng/mL. A validation of the usefulness of this procedure was accomplished by analysing urine extracts obtained from real samples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02275723
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  • 88
    Digitale Medien
    Digitale Medien
    Rapid method for determination of phenylurea herbicides in milk (1994)
    Springer
    Chromatographia 38 (1994), S. 88-92 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Phenylurea herbicides ; Milk
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A method has been developed for the determination of thirteen phenylurea herbicide residues in milk. It involves one-step solvent extraction of the milk with methanol by ultrasonication. The extract is cleaned up on an Amberchrom resin cartridge. Reversed-phase, gradient elution, high-performance liquid chromatography with UV detection at 242 nm is used to analyse the residues. The recovery of thirteen phenylurea pesticides is quantitative, ranging from 71.4% to 97.9% for the individual herbicides investigated at concentrations around 0.05 mg kg−1 and from 65.1% to 95.6% around 0.005 mg kg−1. The method is not associated with any of the emulsion problems common to conventional solvent extraction, which considerably reduce the sample clean-up process compared with existing methods.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02275732
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  • 89
    Digitale Medien
    Digitale Medien
    Statistical evaluation of the validity of a method for characterizing stationary phases for reversed-phase liquid chromatography based on retention of homologous series (1994)
    Springer
    Chromatographia 38 (1994), S. 137-146 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Characterization of reversed phases ; Column hydrophobicity ; Column hydrophylicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The validity of a method for characterizing stationary phases for reversed-phase, liquid chromatography, based on the use of homologous series, has been evaluated. The method is based on a retention model which describes the dependence of the logarithm of the capacity factor on mobile phase composition and the carbon number of specific homologous series. A first-order as well as a second-order version of this model was investigated. The second-order model proved to be a significant improvement on the first-order model, even for smaller mobile-phase ranges. Nevertheless both models showed a significant lack of fit, reflecting the incompleteness of these models. Therefore, it is very questionable whether this method is suitable to describe HPLC-column characteristics like hydrophobicity and hydrophylicity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290326
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  • 90
    Digitale Medien
    Digitale Medien
    Statistical scanning method for the optimization of gradient elution high performance liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 187-190 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Optimal mobile phase ; Gradient elution ; Microcomputer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A computer-assisted method is presented for the optimization of separation in gradient elution reversed-phase HPLC. The method is based on a polynomial estimation from nine preliminary experiments according to a two-factor (initial solvent composition C and gradient time T) rectangular design. This is followed by a two-dimension computer scanning technique. Resolution is used as the selection criterion. Good agreement was obtained between predicted data and experimental results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290335
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  • 91
    Digitale Medien
    Digitale Medien
    Interaction of cyclodextrins with drugs. Chromatographic investigation using a cyclodextrin bonded-phase and its application to chiral separations (1994)
    Springer
    Chromatographia 38 (1994), S. 381-385 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chiral separation ; Association constants ; Frontal analysis ; Cyclodextrin bonded-phases
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The interaction between cyclodextrin and the drug (1R,2S,3S,4S)-(5Z)-7-(3-((phenylsulfonyl)amino)bicyclo[2.2.1]hept-2-yl)hept-5-enoic acid ((+)-S-145), was studied using α-, β-, and γ-cyclodextrin bonded-phase columns. Retention behavior of (+)-S-145 on these columns revealed that the strength of inclusion was β→γ→α-cyclodextrin. Interaction between β-cyclodextrin and (+)-S-145 was found to increase as the proportion of carboxylic ion in the (+)-S-145 molecule increased. Comparison of binding capacities of these bondedsilica gels obtained by frontal analysis and surface coverage indicated that availability of the immobilized β- and γ-cyclodextrin was 20–25%. The synthesized β-cyclodextrin bonded-phase column was superior to that of commercial columns in terms of chiral separation of (±)-S-145. A typical usage of the β-cyclodextrin column is discussed for separation of (±)-S-145 in plasma samples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269784
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  • 92
    Digitale Medien
    Digitale Medien
    Reverse phase high-performance liquid chromatographic determination of primary and secondary aliphatic alcohols as phthalate monoesters by UV detection (1994)
    Springer
    Chromatographia 38 (1994), S. 417-420 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Primary and secondary aliphatic alcohols ; Aqueous derivatization ; Phthalic acid monoesters
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Determination of primary and secondary aliphatic alcohols in aqueous and nonaqueous solutions by high-performance liquid chromatography (HPLC) is described. The alcohol is derivatized with phthalic anhydride to yield the corresponding monophthalate. Separation of the derivative is achieved on an ODS-10 reverse phase (RP) column by elution with an appropriate isocratic mobile phase of acetonitrile and aqueous phosphoric acid (0.1%). Detection is accomplished by UV absorption at 230 nm or 280 nm giving linear calibration plots, for alcohols in aqueous solution from 0.05% to 0.50% (w/v) and in pyridine solution from 0.0025% to 0.0250% (w/v).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269829
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  • 93
    Digitale Medien
    Digitale Medien
    Molecular shape recognition capability of liquid-crystal bonded phases in reversed-phase high performance liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 295-303 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Liquid crystal phases ; Molecular shape recognition ; Polycyclic aromatic hydrocarbons
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The chromatographic retention behaviour of two liquidcrystal bonded phases have been evaluated using polycyclic aromatic hydrocarbons (PAHs) as the probe samples in reversed-phase high performance liquid chromatography (RP-HPLC). The results clearly indicate that these phases have better planarity and shape recognition capabilities than commercially-avaialble polymeric octadecylsilica (ODS) phases whose strong planarity and shape selectivities were found earlier. It can also be concluded from the chromatographic observations that the shape recognition capability of these phases is dependent on both mobile phase composition and column temperature, but that the effect of mobile phase and temperature on the shape selectivity work independently. The retention behaviour can be explained by changes in the phase structure with changes of eluent composition and temperature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269771
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  • 94
    Digitale Medien
    Digitale Medien
    Determination of 6-amino-2,2-dimethyl-1,3-dioxepan-5-ol by postcolumn derivatization witho-phthalaldehyde/2-mercapto-ethanol after ion-pair chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 479-484 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; o-Phthalaldehyde ; Postcolumn derivatization ; Fluorescence detection ; Validation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A high-performance liquid chromatographic method is discribed for the determination of 6-amino-2,2-dimethyl-1,3-dioxepan-5-ol using Spherisorb ODS II stationary phase and mobile phase 30:70 (v/v) methanol: aqueous 1-octane sulfonic acid. Detection was fluorimetric following postcolumn derivatization with o-phthaladehyde/2-mercaptoethanol. The procedure was applied to the analysis of aqueous solutions and microcrystalline suspensions in liquid paraffin, prepared for investigation of the toxicological profile. The method was validated for selectivity, linearity of detector response, repeatability, limit of detection and quantitation. The HPLC method was selective. The instrumental limit of detection was 0.5 ng per injection (0.05 μg mL−1). The method detection limits were 0.5 μg mL−1 aqueous solution and 5 μg mL−1 liquid paraffin suspension, the quantitation limit 0.05 mg mL−1 aqueous solution and 1.0 mg mL−1 liquid paraffin. Linearity was within 0.94–47.1 μg mL−1. Intra-assay accuracy accounted for 99–100% in the range 0.05–226 mg mL−1 aqueous solution, intra-assay precision for 2% (C.V.). For microcrystalline liquid paraffin suspensions with 1 and 250 mg mL−1 99 and 109% was found for intra-assay accuracy. Intra-assay precision was 5% (C.V.). Reliable results over a wide concentration range can be obtained. The procedure is considered valid for determination of the analyte in aqueous solution or microcrystalline paraffin oil suspensions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269840
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  • 95
    Digitale Medien
    Digitale Medien
    Ligand-exchange chromatography of amino acid enantiomers and its application to the biotransformation of DL-aspartic acid byPseudomonas dacunhae (1994)
    Springer
    Chromatographia 39 (1994), S. 15-22 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Ligand exchange ; Amino acid enantiomers ; DL-aspartic acid ; Pseudomonas dacunhae
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The separation of the D and L enantiomers of eighteen essential α amino acids has been investigated by ligand-exchange chromatography (LEC). The effect of column temperature on the retention times and resolution of individual amino acid enantiomers has been studied by varying the temperature from 25 to 50 °C for a mobile phase containing Cu2+ ions. By use of a temperature of 50 °C and Zn2+ in the mobile phase, eight of the eighteen amino acid enantiomers can be resolved sufficiently well for practical application. Only phenylalamine, tyrosine, and tryptophan can be separated by use of Ni2+ as complexation metal at 50 °C. LEC has been used to monitor the decarboxylation of racemic DL-aspartic acid byPseudomonas dacunhae. Analysis of DL amino acid enantiomers in different media was performed at column temperatures of 30 and 50°C by addition of 0.125 mM Cu2+ to the aqueous mobile phase. It was found that the analytical performance is most dependent on the identity of the metal used for complexation; the concentration of the metal was of secondary importance and the column temperature less important still.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02320452
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  • 96
    Digitale Medien
    Digitale Medien
    System peaks in single column ion chromatography (SCIC) with indirect spectrophotometric detection (1994)
    Springer
    Chromatographia 39 (1994), S. 713-718 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Ion chromatography ; System peaks ; Indirect detection ; Anions and cations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The most popular eluents for SCIC are organic acids and their salts with one or more kinds of ion taking part in the elution process. These ions compete for ion-exchange equilibria. After an injection, the equilibria are disturbed and a re-equilibration process occurs resulting in extraneous peaks (system peak). A mechanism based on these aspects is proposed which is used successfully in the interpretation of the effects of sample properties and eluent parameters on system peaks. Experiments in the analysis of both cations and anions have been carried out to support this mechanism with eluents comprising two kinds of eluent ions. An equation for capacity factors in such systems is also derived.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274588
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  • 97
    Digitale Medien
    Digitale Medien
    Enantiomeric separation of amphetamine, methamphetamine and ring substituted amphetamines by means of a β-cyclodextrin-chiral stationary phase (1994)
    Springer
    Chromatographia 39 (1994), S. 131-137 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chiral separation ; Amphetamine ; Cyclodextrin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The enantioseparation of amphetamine, methamphetamine and various ring-substituted amphetamines by use of a chiral stationary phase carrying immobilized native β-cyclodextrin (β-CyD) selectors is reported. The system is evaluated for resolving the specified compounds directly without any derivatization and after derivatization with phenyl isothiocyanate (PITC), naphthyl isothiocyanate (NITC) and 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC). This direct enantioseparation is compared with the features of indirect separation of diasteromeric derivatives after reaction with the optically pure Marfey's reagent employing a simple non-chiral alkyl-silica (RP-8) column. A selection of those methods best suited for each single amphetamine is given. Seventeen different samples of amphetamine, confiscated by the Swedisch police, were analyzed with respect to their enantiomeric composition. Within this set of samples synthesized by the same method no significant deviation from a racemic ratio could be observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274491
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  • 98
    Digitale Medien
    Digitale Medien
    Separation of polycyclic aromatic hydrocarbons under isocratic conditions by a column switching technique (1994)
    Springer
    Chromatographia 39 (1994), S. 175-179 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Column switching ; Columns at different temperatures ; Polycyclic aromatic hydrocarbons
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A simple and efficient method of separating a 20-component PAH-mixture (RSM 1647 standard mixture +benzene, toluene, perylene and coronene) by RP-HPLC is described. Separation was by using two Superspher-100 RP-18 cartridges thermostatted at different temperatures under isocratic conditions with water-acetonitrile eluent. The analysis time with complete resolution of all components can be reduced to 15 min.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274497
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  • 99
    Digitale Medien
    Digitale Medien
    A novel derivatisation procedure for inorganic mercury(II) for HPLC analysis (1994)
    Springer
    Chromatographia 39 (1994), S. 246-248 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Mercury ; Diphenylethynylmercury
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A new procedure for derivatisation of inorganic mercury(II) to diphenylethynylmercury with simultaneous extraction into dichloromethane is proposed. The organomercury derivative is effectively analysed by HPLC using UV detection. The calibration curve is linear over three orders of magnitude (0.02–50 mg L−1 Hg); the detection limit is 0.1 ng Hg. A preliminary study of the effect of potential interfering agents, in particular Cu(II), Zn(II), Cd(II), Pb(II), and cysteine, and applications of the present methodology to real environmental samples are presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274507
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  • 100
    Digitale Medien
    Digitale Medien
    Salt effects in anion exchange displacement chromatography: Comparison of pentosan polysulfate and dextran sulfate displacers (1994)
    Springer
    Chromatographia 39 (1994), S. 409-418 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Ion-exchange chromatography ; Protein purification ; Pentosan polysulfate displacers ; Dextran sulfate displacers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Experimental studies were carried out to investigate the utility of pentosan polysulfate as a low molecular weight polyelectrolyte displacer for the purification of proteins in anion-exchange displacement systems. In addition, the influence of mobile phase salt concentration on displacer efficacy, protein-protein resolution, and displacement development were studied for several anionic displacers. It was found that while large polyelectrolytes (50 kd dextran sulfate) were efficient displacers for a wide range of salt concentrations, relatively small polyelectrolytes (3 kd pentosan polysulfate) were seen to act as an efficient displacer only under conditions of high salt micro-environments. In addition, for proteins exhibiting similar affinities, zone mixing at the protein-protein boundary was found to be quite sensitive to the salt concentration. Finally, displacement chromatography was successfully implemented for the separation of proteins from milk whey.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278755
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