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  • Column liquid chromatography  (844)
  • Gas chromatography  (336)
  • General Chemistry
  • Humans
  • Inorganic Chemistry
  • Springer  (1,177)
  • 2015-2019
  • 1990-1994  (659)
  • 1985-1989  (518)
  • 1935-1939
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  • 1
    Electronic Resource
    Electronic Resource
    2,6-Di-O-pentyl-3-O-propionyl-γ-cyclodextrin as an enantiomeric stationary phase for capillary gas chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 22-28 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Chiral separation ; Capillary column ; 2,6-Di-O-pentyl-3-O-propionyl-γ-cyclodextrin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 2,6-Di-O-pentyl-3-O-propionyl-γ-cyclodextrin has been synthesized and used for enantiomer separation in capillary gas chromatography. Experimental results showed that the stationary phase has good enantiomer selectivity toward amino acids, amines, alcohols, diols, epoxides, and lactones,etc. 2,6-Di-O-pentyl-3-O-propionyl-γ-cyclodextrin has good thermal stability: the highest recommended temperature isca 170°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275722
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Column-switching ; Determination of triamterene ; Fluorescence detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275723
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Characterization of reversed phases ; Column hydrophobicity ; Column hydrophylicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290326
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Copoly(styrene/acrylonitrile) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269631
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Chiral recognition ; Aminoalkylphosphonic acid derivatives ; β-cyclodextrin bonded phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269635
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of pentachlorophenol residues in wine and corks by solvent extraction methodology and specific gas chromatography detection (1994)
    Springer
    Chromatographia 38 (1994), S. 147-150 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Pentachlorophenol residues ; Off-flavours ; Wines and corks ; Electrolytic conductivity detector/mass spectrometry ; detectors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic methodology with selective detection is presented for the analysis in wines and corks of pentachlorophenol residues, which are suspected to be the most likely precursors of some off-flavours described in several wine samples. After derivatisation, pentachlorophenol acetate residues were monitored by electrolytic conductivity detection and/or mass spectrometric detection in the selective ion mode at m/z 264 and 266. Recoveries varied from 80 to 96% for wine samples fortified with 5 to 100 μg l−1 and from 83 to 91% for corks (fortified at 25 to 100 μg kg−1). The proposed methodology allowed for a determination limit of μg l−1 for wine and 10 μg kg−1 for corks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290327
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  • 7
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Chiral separation ; Association constants ; Frontal analysis ; Cyclodextrin bonded-phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269784
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  • 8
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Primary and secondary aliphatic alcohols ; Aqueous derivatization ; Phthalic acid monoesters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269829
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  • 9
    Electronic Resource
    Electronic Resource
    Capillary gas chromatography of plant tissues and soil phenolic acids (1994)
    Springer
    Chromatographia 38 (1994), S. 475-478 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Phenolic acids ; Olive and elm tree tissues ; Soil phenolics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for the separation of phenolic acids along with shikimic and quinic acids by means of capillary gas chromatography is described and discussed. The method involves the previous derivatization of the acids to trimethylsilyl derivatives and it has been applied to the separation of acids extracted from olive leaves and roots, elm leaves and a soil A horizon. Quite good results were achieved both from qualitative and quantitative points of view. Qualitative differences have been pointed out in the phenolic acid composition of two olive cultivars and between leaves and roots of the same cultivar; also two elm species can be discriminated on the basis of the phenolic acid content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269839
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  • 10
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Hybrid mobile phases containing alcohols ; Solute-micelle association constants ; Polynuclear aromatic hydrocarbons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269778
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  • 11
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Wine ; Biogenic amines ; Solid-phase extraction ; Derivatization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277156
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  • 12
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Chiral/enantiomeric iseparation ; Cellulose-based chiral phases ; Tifluadom analogues ; 2-acylaminomethyl-1,4-benzodiazepines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277166
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  • 13
    Electronic Resource
    Electronic Resource
    Characterization of methacrylic ester of p, p′-dihydroxydiphenylpropane diglicydyl ether-divinylbenzene porous copolymers for GC (1994)
    Springer
    Chromatographia 38 (1994), S. 643-648 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Porous polymer stationary phase ; Selectivity studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The behaviour of GC columns packed with the copolymer of methacrylic ester of p,p'-dihydroxydiphenylpropane diglicydyl ether and divinylbenzene was studied. Selectivity studies were made for three polymer samples of different molar ratio of monomers. To determine the selectivities of these copolymers retention indices for seven test compounds in comparison to those obtained on Porapak Q are calculated. Additionally, the efficiency of porous polymer purification was studied by a SFE-GC-MS technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277169
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  • 14
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Phenolic compounds ; Ion-pair solid-phase extraction ; Comparison of sorbents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277157
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  • 15
    Electronic Resource
    Electronic Resource
    Enantiomeric separation of amphetamine and methamphetamine by capillary gas chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 595-598 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Chiral / enantiomeric separation ; Amphetamine ; Methamphetamine ; Cyclodextrin-derivatized phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Enantiomeric separation of amphetamine and methamphetamine as achiral derivatives on 2,6-di-O-pentyl-3-O-trifluoroacetyl-β-cyclodextrin, 2,6-di-O-pentyl-3-O-trifluoroacetyl-γ-cyclodextrin and 2,6-di-O-pentyl-3-O-propionyl-γ-cyclodextrin stationary phase in capillary gas chromatography is described. Trifluoroacetic anhydride and acetic anhydride were used as derivatizing reagents. Excellent precision was obtained for concentrations down to 0.1% / e.e. On 2,6-di-O-pentyl-3-O-propionyl-γ-cyclodextrin the elution order of R,S-amphetamine was reversed when the derivatizing reagent was changed but could not be reversed on any of the other phase types.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277160
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  • 16
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Extraction-determination ; Basic drugs ; Blood
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277164
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  • 17
    Electronic Resource
    Electronic Resource
    Rapid magnetic particle-based ELISA assay compared with gas chromatography-nitrogen phosphorus detection for determining atrazine in freeze-dried water samples (1994)
    Springer
    Chromatographia 38 (1994), S. 633-636 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Nitrogen phosphorus detection ; Atrazine and simazine ; Freeze-dried water analysis ; ELISA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The determination of atrazine in freeze-dried water samples containing simazine, 0.6% glycine as stabilizer and other pesticides has been compared using three different techniques: (i) direct rapid-magnetic particlebased ELISA, (ii) dichloromethane liquid-liquid extraction (LLE) and Florisil column clean-up prior to ELISA determination and (iii) LLE, Florisil column clean-up and gas chroamtography with nitrogen phosphorus detection (GC-NPD). The methodology developed in this paper has shown the advantages of the introduction of a clean-up step prior to ELISA determination and its correlation with GC-NPD determinations. Atrazine could be determined at levels between 0.1 to 5 μg l−1 in water smaples using the different methods described in this paper. The crossreactivity problems found in the ELISA test associated with the presence of simazine are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277167
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  • 18
    Electronic Resource
    Electronic Resource
    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
    Keywords: Column liquid chromatography ; Column switching ; Imidazolinone herbicides in soil ; Imazethapyr ; Imazapyr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02320459
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  • 19
    Electronic Resource
    Electronic Resource
    An improved gas chromatographic assay for spectinomycin hydrochloride (1994)
    Springer
    Chromatographia 39 (1994), S. 71-73 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Spectinomycin ; Silylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic assay for spectinomycin hydrochloride is described. The method is based on that prescribed by the United States Pharmacopeia (USP XXII). The method involves silylation of spectinomycin hydrochloride; phenazone is used as an internal standard. Spectinomycin and phenazone have adequate stability under the prescribed conditions. The stationary phase is 3% OV-17 on Gaschrom Q 100–120 mesh. The selectivity of the proposed method is better than that of the GLC method described in the USP XXII.
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    URL: http://dx.doi.org/10.1007/BF02320461
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  • 20
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    Enantiomer separation of side-chain fluorinated alkylbenzenes by capillary gas chromatography on cyclodextrin phases (1994)
    Springer
    Chromatographia 39 (1994), S. 192-199 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Enantiomer separation ; Permethylated cyclodextrin stationary phases ; Side-chain fluorinated alkylbenzenes ; Thermodynamic data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of racemic side-chain fluorinated alkylbenzenes and bromofluorinated analogues by capillary gas chromatography using permethylated α, β and γ-cyclodextrins dissolved in polysiloxanes of different polarity as stationary phases is described. The influence of the achiral polysiloxane matrices on the separation of enantiomers is discussed in the light of the results obtained with the different phases. For a part of the tested compounds thermodynamic data are determined which describe the interaction of enantiomers with the stationary phase. The mechanism of separation is discussed on this basis and by comparison with data for structurally similar compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274500
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  • 21
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    A novel derivatisation procedure for inorganic mercury(II) for HPLC analysis (1994)
    Springer
    Chromatographia 39 (1994), S. 246-248 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mercury ; Diphenylethynylmercury
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274507
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  • 22
    Electronic Resource
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    Ruggedness testing of gas chromatographic method for residual solvents in pharmaceutical substances (1994)
    Springer
    Chromatographia 39 (1994), S. 355-362 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Method validation ; Reggedness test ; Residual solvents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ruggedness testing is performed on a gas chromatographic method for the quantitative determination of residual solvents in steroids. Eight experimental variables or factors which were expected to influence the quantitative results were selected. These factors were divided into two independent groups, i.e. four factors related to the injection process and four factors related to separation and detection. In order to determine interaction between factors and quadratic effects, a central composite design was selected for the set-up of the experiments. Because in the method an internal standard is used, relative peak area was used as response. A deviation of up to 2.5% per factor for the quantitative results was regarded as acceptable. Other responses studied are related to the system suitability. Observed main, quadratic and interaction effects were translated into rugged intervals of the experimental variables by graphical presentation. It was found that besides main effects significant interaction effects were present, for example between the temperature of the injector and the split-flow. Interaction effects can easily result in the reduction of the rugged intervals by a factor of 2. The calculated rugged intervals were compared with the precision of the instrument or factor settings in order to estimate the ruggedness of the factors. Eventually, the maximum effect of the variation in the instrument settings on the quantitative results regarding the precision of the factor settings was found to be only 2.2%. Overall, the method proved to be rugged for most factors, except for the split-flow of the injector for which the method was only rugged to a limited extent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274525
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  • 23
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    Effect of ester molecular structure and column temperature on the retention of eight esters in gas chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 438-442 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention/structure and retention/temperature ; relationships ; Experimental design ; Enthalpy-entropy compensation ; para-Hydroxy benzoic esters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An experimental design has been used to study the effect of column temperature on the gas chromatographic retention of eightpara-hydroxy benzoic esters. A rapid procedure has been developed to reduce the number of experiments compared with traditional methods. Capacity factors were determined and the enthalpy and entropy of transfer from the mobile phase to the stationary phase, ΔHo and ΔSo, respectively, were calculated using the linear Van't Hoff equation (dependence of ln k′ on 1/T). A retention prediction system (RPS) for these compounds in GC was investigated. The molecular connectivity index was used to describe the quantitative structure relationships. Enthalpy — entropy compensation revealed that the mechanism was similar for all the compounds studied.
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    URL: http://dx.doi.org/10.1007/BF02278759
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    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
    Keywords: Column liquid chromatography ; Ion exclusion ; Alipathic acids ; Silage effluents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02275725
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    A very efficent column for the separation of 60 volatile organochlorine priority pollutants and for other environmental problems (1994)
    Springer
    Chromatographia 38 (1994), S. 114-117 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Priority pollutants ; EPA methods ; Unleaded gasoline ; Volatile organochlorine compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The complete separation of the sixty volatile organochlorine (VOC) priority pollutants has been achieved by coupling two different liquid-modified adsorption chromatography columns. Two temperature programs were used to obtain the complete separation in a relatively short analysis time. Detection was by FID alone
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    URL: http://dx.doi.org/10.1007/BF02275736
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    Influence of adsorption effects on retention indices of selected C10-hydroxy compounds at various temperatures (1994)
    Springer
    Chromatographia 38 (1994), S. 93-97 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention index ; Adsorption effects ; Terpene alcohols ; Fused-silica capillary columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention indices of 6 selected hydroxy compounds (aliphatic and bicyclic alcohols, phenols) were determined on 2 HP-5 fused-silica, capillary columns with different film thicknesses (0.11 μm and 0.33 μm) at 8 different oven temperatures between 80 and 150°C. For some substances the I-T plot was found to show a minimum which cannot be explained by the common retention-index temperature-dependence in gas-liquid chromatography. This result is discussed in terms of adsorption at the liquid-solid interface of the capillary column.
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    URL: http://dx.doi.org/10.1007/BF02275733
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    Molecular structural coefficients of Takács. Their dependence on column temperature, stationary phase polarity and solute chemical nature (1994)
    Springer
    Chromatographia 38 (1994), S. 701-708 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Stationary Phase and solute polarity ; Molecular structural coefficients ; Retention index ; Takács equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Molecular structural coefficients, Sc, for one hundred solutes have been calculated by means of the Takács equation using retention data obtained with over fifty stationary phases, SP. Employing data of seven SP's (characterized in our laboratories) it was found that the variation of Sc with column temperature was linear for most solutes. With data of n-decane and the ten McReynolds probes on up to fifty SP's of polarity less than RP=72, at 120°C, it was found that the Sc of n-decane and cis-hydrindane decreased slightly with increasing SP polarity, while the Sc of non-alkanes remained constant or increased very little as the SP polarity increased. The points for n-decane fit well to a second order polynomial. Again using a temperature of 120°C, the increments of Sc for solutes belonging to an homologous series were correlated with the polarity of SP's. Reasonably straight lines were obtained for all the chemical functions studied, Sc increasing with increasing SP polarity.
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    URL: http://dx.doi.org/10.1007/BF02269624
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    Polymer encapsulated packing material for reversed phase liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 756-760 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polymer encapsulated packings ; Poly(ethylstyrene-divinylbenzene) ; Preparation and evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02269632
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; β-Cyclodextrin in mobile phase ; Estrogens ; Pregnant and non-pregnant women
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02290331
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    Convergence of retention for small solutes in reversed-phase liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 158-162 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reversed-phase chromatography ; Retention mechanism ; Retention convergence ; Small molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02290329
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    Characterization of some new polysiloxane stationary phases by principal component analysis (1994)
    Springer
    Chromatographia 38 (1994), S. 227-231 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Stationary phase characterization ; Principal component analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this study, several new stationary phases were characterized by principal component analysis. Fourteen new stationary phases, including substituted phenyl and oligoethyleneoxide functionalities on polysiloxane polymers, were tested and compared to three well known stationary phases. The main features of these phases were studied using a series of test solutes of varying chemical characteristics representing the data set for principal component analysis. Two principal compounds were found to account for 99.20% of the variance (the first accounted for 94.96% and the second for 4.24%). The data were represented as a two-dimensional map for visual representation of the characteristics of these stationary phases. The first principal component represented a selectivity based on polarity (r2=0.998), while the second showed Lewis acid-base characteristics of the phases. Polarizable and amphoteric characteristics of these phases also became evident using this evaluation method.
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    URL: http://dx.doi.org/10.1007/BF02290341
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    CP/MAS NMR investigations of silica gel surfaces modified with aminopropylsilane (1994)
    Springer
    Chromatographia 38 (1994), S. 283-290 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemically bonded phase (CBP) ; Silica-gel with aminopropylsilyl ligands ; Physico-chemical characterization ; CP/MAS NMR investigation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02269769
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    The application of ‘Z’-shaped UV cells in open-tubular capillary column liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 313-316 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Open-tubular capillary columns ; ‘Z’-shaped UV cells ; Solvent make-up
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02269773
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    Interconversion of cyclosporin molecular form inducing peak broadening, tailing and splitting during reversed-phase liquid chromatography (1994)
    Springer
    Chromatographia 38 (1994), S. 359-364 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cyclosporin ; Reversible conversion ; Activation energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02269781
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    Determination of carbendazime in lettuce samples by SFE-HPLC (1994)
    Springer
    Chromatographia 38 (1994), S. 395-399 
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    ISSN: 1612-1112
    Keywords: Supercritical fluid extraction ; Column liquid chromatography ; Carbendazime analysis ; Vegetable samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02269786
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    A photometric flow measurements method for characterisation of HPLC pumps (1994)
    Springer
    Chromatographia 38 (1994), S. 421-430 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Pumps ; Flow control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02269830
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    Comparison of supercritical fluid extraction and liquid-liquid extraction for isolation of selected pesticides stored in freeze-dried water samples (1994)
    Springer
    Chromatographia 38 (1994), S. 502-508 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid-liquid extraction ; Supercritical fluid extraction ; Pesticides ; Freeze-dried water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The stability of freeze-dried water samples spiked with eight agrochemicals (atrazine, simazine, linuron, carbaryl, propanil, fenitrothion, parathion and fenamiphos) were examined to evaluate their suitability as candidate reference materials for their determination in water samples. In addition, two different extraction procedures, liquid-liquid and supercritical fluid extraction, were compared for the isolation and trace enrichment of target analytes from freeze-dried water samples. Final analytical determinations were by gas chromatography-nitrogen phosphorus detection and electronic impact mass spectrometry, and by liquid chromatography-diode array detection. The whole methodology developed in this paper permitted the determination of pesticides spiked in water at levels varying from 0.03 to 6.9 μg L−1.
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    URL: http://dx.doi.org/10.1007/BF02269843
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    Determination of bromoxynil and ioxynil residues in cereals and soil by GC-ITD (1994)
    Springer
    Chromatographia 38 (1994), S. 624-628 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Ion-trap detection ; Nitriles ; Cerelas ; Perfluoroacylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Bromoxynil and ioxynil have been determined inplants and soil by gas chromatography. These herbicides are extracted from soil samples with methylene chloride at acidic pH. Plant samples are extracted with a basic acqueous solution and extracts purified by solvent partitioning. Herbicide residues are submitted to perfluoroacylation prior to GC separation. These compoiunds are determined by ion-trap detection with single ion monitoring; N-(3-chloro-4 methyl-phenyl_ perfluoropropyl amide is used as internal standard. The detection limit of the method is near 0.001 μg g−1 for the samples studied. The proposed methods are sensitive and reproducible enough to allow determination of these herbicides at residue levels in plants and soil.
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    URL: http://dx.doi.org/10.1007/BF02277165
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    Surface modification by calcium ions—Effect on chromatographic properties of silica (1994)
    Springer
    Chromatographia 39 (1994), S. 29-34 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Calcium modified silica ; Calcium adsorption isotherms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02320454
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    Supercritical fluid extraction of oxadixyl from food crops (1994)
    Springer
    Chromatographia 39 (1994), S. 11-14 
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    ISSN: 1612-1112
    Keywords: Supercritical fluid extraction (SFE) ; Gas chromatography ; Pesticide residues ; Oxadixyl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This work describes the study of a degradation curve of Oxadixyl in field-treated potato and tomato samples. The residues were extracted using classical and supercritical fluid (SFE) extraction methods and analyzed by HRGC/ECD. The extraction techniques were compared and the results indicate the advantages of using SFE as an alternative method for pesticide analyses in these samples.
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Sample preconcentration ; Solid-phase extraction ; Solvent focussing ; Injection techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    An improved method for the determination of free sphingosine in serum (1994)
    Springer
    Chromatographia 39 (1994), S. 85-90 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; Carbopack B ; Free sphingosine in human plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: Column liquid chromatography ; Atmospheric pressure chemical ionization-mass spectrometry ; Dried yeast ; Thiamine ; Ion-pair extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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].
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    An improved high-performance liquid chromatographic determination of chlorpropamide in human plasma (1994)
    Springer
    Chromatographia 39 (1994), S. 107-109 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Drug assay ; Chlorpropamide ; Tolbutamide ; Human plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: Column liquid chromatography ; Chemically bonded phases ; Non-silica based supports ; Hydrosilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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
    Keywords: Column liquid chromatography ; Continuous beds ; Compressed beds ; Proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02274579
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    Reversed phase C18 packings for the separation of polycyclic aromatic hydrocarbons by high performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 668-672 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Monomeric and oligomeric RP packings ; Preparation of RP stationary phases ; Polycyclic aromatic hydrocarbons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02274581
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    Analysis of short chain fatty acids from different intestinal samples. I: By packed column gas chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 706-712 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Short chain fatty acids ; Intestinal fluids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The quantification of short chain fatty acids in their free form, by gas chromatography, is the method of choice provided that the underivatized acids elute with good peak shape and reproducibility. In biological samples not only the highly polar acids themselves but also deposits of nonvolatile sample components may interact with the column or the packing material. As a result, the peak symmetry of the fatty acids and their reproducibility can become increasingly poor. Reduction of the nonvolatile matrix components by filtration of the sample has been examined in order to achieve direct analysis of the short chain fatty acids in intestinal samples by packed column GC. Membrane filter units (0.8 μm) allow a quick and simple filtration of the samples. This pretreatment reduces the peak tailing and the broadening of the peaks. The method, when applied to different intestinal samples, allowed the quantification of short chain fatty acids in hundreds of samples without derivatization. Good results are obtained at sample concentrations higher than 0.2 mmol l−1 for each acid.
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    Estimation of phenolic compounds in green pepper berries (Piper nigrum L.) by high-performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 743-746 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Phenolic compounds ; Green pepper berries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02274592
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    Analysis of basic hair dyes by HPLC with on-line post-column photochemical derivatisation (1994)
    Springer
    Chromatographia 39 (1994), S. 138-145 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Diode array detection ; Post-column photochemical derivatisation ; Hair dyes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Copoly(styrene/ethyl methacrylate) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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).
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    Capillary gas chromatography of C1−C4 alkyl tert-butyl ethers (1994)
    Springer
    Chromatographia 39 (1994), S. 224-227 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; C1−C4 alkyl tert-butyl ethers ; Retention index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of C1−C4 alkyl tert-butyl ethers with the general formula (CH3)3C−O−R (R-alkyl substituent) on fused-silica capillary columns coated with dimethylsilicone and cyanopropylmethylsilicone stationary phases was investigated. Retention indices were determined at two temperatures in order to understand their chromatographic behaviour. The respective standard deviations were 0.3 and 0.5 i.u.
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Membrane-extraction disks ; On-line trace enrichment ; Polar pollutants ; Surface water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Retention characteristics of fluorinated bonded silica phase in reversed-phase liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 285-293 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fluorinated chemically bonded silica ; Aromatic compounds ; Molecular shape vs. retention
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    GC-NPD investigation of the recovery of organonitrogen and organophosphorus pesticides from apple samples: The effect of the extraction solvent (1994)
    Springer
    Chromatographia 39 (1994), S. 320-324 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Organonitrogen pesticides ; Organophosphorus pesticides ; Apples ; Solvent extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method employing a capillary column and a selective nitrogen/phosphorus detector (NPD) has been developed for the determination of organophosphorus (OP) and organonitrogen (NP) pesticides in horticultural samples (apples). The separation of sixteen pesticides and the internal standard was performed in thirteen minutes. The analytical characteristics of the method, including linear response ranges, detection limits, and reproducibility, have been studied using a 1∶1 mixture of ethyl acetate and xylene as extraction solvent. The possibility of mutual interference between pesticides has also been studied. A procedure for the quantitative extraction of the sixteen pesticides from apple samples has also been developed; for fifteen of the pesticides recoveries 〉85% were obtained after 90 minutes extraction. The effect of different solvents both on recovery and on the sensitivity of the subsequent chromatography were also investigated. It was found that the sensitivity required must be considered when the solvent for sample treatment is selected.
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    Optimization of mobile phases for HPLC of cis-trans carotene isomers (1994)
    Springer
    Chromatographia 39 (1994), S. 346-354 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; α-Carotene cis-isomers ; β-Carotene cis-isomers ; Polymer stationary phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Chromatographic determination of D-amino acids as native constituents of vegetables and fruits (1994)
    Springer
    Chromatographia 39 (1994), S. 419-426 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Chirasil-Val ; Amino acid enantiomers ; N-Isobutyryl-cysteine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Temperature effect in separation of fullerene by high-performance liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 453-459 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fullerenes ; Octadecylsilicas ; Temperature effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Phenolic compounds ; Poplar bark ; Discosporium populeum infection ; Chemometric data evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Determination of catecholamines in urine by micellar liquid chromatography with coulometric detection (1994)
    Springer
    Chromatographia 39 (1994), S. 591-596 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar liquid chromatography ; Catecholamines in urine ; Coulometric detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Improved separation of diastereoisomers in capillary electrophoresis using a mixture of β-cyclodextrin and sodium taurodeoxycholate (1994)
    Springer
    Chromatographia 39 (1994), S. 627-630 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar electrokinetic capillary electrophoresis ; Tetrahydrocarbazole derivatives ; β-Cyclodextrin ; Taurodeoxycholate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Determination of sugars by liquid chromatography with post-column catalytic derivatization and fluorescence detection (1994)
    Springer
    Chromatographia 38 (1994), S. 12-16 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carbohydrates ; Post-column fluorescence derivatization ; Post column catalytic reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Chromatography of esculin from stems and bark ofAesculus hippocastanum L. for consecutive vegetative periods (1994)
    Springer
    Chromatographia 38 (1994), S. 766-770 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin-layer chromatography ; Densitometry ; Spectrophotometry of extracts ; Esculin, fraxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Linearization of column responses by correlation chromatography. Separation improvement and reduction of undesired adsorption effects (1994)
    Springer
    Chromatographia 38 (1994), S. 62-70 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Correlation chromatography ; Simulation model ; Adsorption effects ; Separation improvement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram. A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well.
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    Rapid method for determination of phenylurea herbicides in milk (1994)
    Springer
    Chromatographia 38 (1994), S. 88-92 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Phenylurea herbicides ; Milk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Gas chromatographic water analysis by direct injection of large sample volumes in an adsorbent-packed PTV injector (1994)
    Springer
    Chromatographia 38 (1994), S. 694-700 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; PTV injection system ; Aqueous samples ; Pesticides ; Breakthrough volumes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A GC method is described for the determination of pollutants in aqueous samples by direct enrichment out of large sample volumes in a PTV injector. The vaporized water is eliminated through the split vent and the analytes are concentrated on an adsorbent inside the insert of the PTV. For the selection of suitable adsorbents, breakthrough volumes of selected pesticides and nitroaromatics on Tenax TA, Tenax GR, Chemipack C18 and graphitized carbon blacks have been determined by experiment. The determination of the breakthrough volumes was carried out directly in the PTV insert. Tenax TA proved to be the best sorbent with regard to the breakthrough volumes and its inertness to the analytes to be determined. As the result of the investigations, 500 μl of aqueous standard solutions of pesticides and nitroaromatics (concn.=0.02 ... 2 μg/l) were analyzed with an average relative standard deviation of 10%. The procedure was successfully applied for the analysis of real samples.
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    Chromatographic determination of the rate and extent of absorption of air pollutants by sea water (1994)
    Springer
    Chromatographia 38 (1994), S. 191-198 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Reversed-flow technique ; Absorption rate ; Air pollutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple chromatographic method is developed to determine the rate constant for expulsion of an air pollutant from water or its diffusion parameter in the liquid, the rate constant for chemical reaction of the pollutant with water, its mass transfer coefficient in the liquid, and the partition coefficient between liquid water and air. From these physicochemical parameters, the absorption rate by sea water and, therefore, the depletion rate of a polluting substance from the air can be calculated, together with the equilibrium state of this absorption. The method has been applied to nitrogen dioxide being absorbed by triple-distilled water and by sea water, at various temperatures. From the temperature variation of the reaction rate constant and of the partition coefficient, the activation energy for the reaction and the differential heat of solution were determined.
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    URL: http://dx.doi.org/10.1007/BF02290336
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    Lipid class analysis by normal phase high performance liquid chromatography, development and optimization using multivariate methods (1994)
    Springer
    Chromatographia 38 (1994), S. 317-324 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Lipid class analysis ; Experimental design and optimization ; Chemometrics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02269774
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    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
    Keywords: Column liquid chromatography ; Micellar liquid chromatography ; Determination of catecholamines ; Aminochromes ; Thermal lens spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02269782
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    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
    Keywords: Column liquid chromatography ; Copoly(styrene/ethyl methacrylate) ; Gradient elution, sudden transition ; Precipitation chromatography of polymers ; Solubility of polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02277154
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ligand exchange ; Amino acid enantiomers ; DL-aspartic acid ; Pseudomonas dacunhae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02320452
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    Retention and selectivity of aromatic hydrocarbons with mono-substituted polar groups in ternary RP-HPLC systems (1994)
    Springer
    Chromatographia 39 (1994), S. 67-70 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reversed phase systems ; Ternary eluents ; Mono-substituted aromatics ; Retention and selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02320460
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Column switching ; HIV type 1 reverse transcriptase inhibitor ; Acquired immune deficiency syndrome ; L-697, 661
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02320463
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    Reversed phase behaviour of high molecular mass polystyrenes in ethyl acetate solvent mixtures (1994)
    Springer
    Chromatographia 39 (1994), S. 663-667 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polystyrene ; Ethyl acetate ; Dichloromethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02274580
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    Static headspace gas chromatography of residual solvents in pharmaceutical products (1994)
    Springer
    Chromatographia 39 (1994), S. 645-648 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace analysis ; Gonadotrophins ; Residual solvents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A headspace, gas chromatographic method for determining residual solvents in pharmaceutical products such as the gonadotrophin powders, has been developed. The method allows the determination of residual solvents by transferring the samples directly into a vial contianing 10 mL 2M sodium chloride; the analysis is carried out by sampling the headspace and separating by capillary gas chromatography using a programmedtemperature vaporizer (PTV) injector. The procedure described is simple, sensitive and reproducible. The lower limit of detection is 20 ppb for ethyl alcohol, 8 ppb for acetone and 0.5 ppb for diethyl ether.
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    URL: http://dx.doi.org/10.1007/BF02274577
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    Comparison of sample concentration methods and correlation chromatography for polymer dynamic head-space studies (1994)
    Springer
    Chromatographia 39 (1994), S. 210-215 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Correlation chromatography ; Concentration methods ; Polymer dynamic head-space sampling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatography has been used to study the kinetics of evolution of volatiles from polypropylene samples (at 70°C). Correlation chromatography (CC) and the trapping of volatiles on Tenax sorbents and activated charcoal were employed to improve the detector signal. As a reference, the kinetics of gas evolution was studied by making a series of direct single injections of polymer head-space gas on a GC column. The results of trapping differed from those obtained by single injection. However, the data from single injections and CC were in good agreement. The CC method was found to offer far more operator convenience for dynamic head-space analysis than sample trapping, being less subject to operator errors.
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    URL: http://dx.doi.org/10.1007/BF02274502
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; LC/MS coupling ; Particle Beam interface ; Plasma and urine samples ; BN50730 and its metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02274505
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    Generation of split-flow micro-gradients for capillary HPLC (1994)
    Springer
    Chromatographia 39 (1994), S. 279-284 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary columns for LC ; Micro-gradient generation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02274514
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    Comparison of packed and capillary columns for quantitative gas chromatography of triglycerides in milk fat (1994)
    Springer
    Chromatographia 39 (1994), S. 265-270 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Triglycerides ; Packed vs. capillary columns ; Milk fat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Quantitative gas chromatography of triglycerides in conjunction with established triglyceride formulae can be used to determine various milk fat parameters. Since the evaluation of, for example, iodine number or content of non-milk fats (foreign fats) in milk fat requires only the separation of triglycerides by carbon number and since repeatabilities, especially of the highboiling triglycerides, have been less acceptable with capillary columns in the past, packed columns have been used exclusively. There is, however, an increasing demand for the use of capillary instead of packed columns and to that end the present investigation has been carried out. To achieve a suitable resolution, with this particularly exacting high-temperature application, a short 5 m capillary column of extreme temperature stability has been used. As well as modification of various analytical conditions different injection techniques have been investigated. On-column, PTV and split injection were compared with regard to repeatability. The cold-on-column injection technique was found to produce the best results, being comparable to the excellent precision of a packed column. Thus, a method is now available by means of which the determination of milk fat parameters by the triglyceride formulae, such as the amount of foreign fats in milk fat, can now be carried out with a standardized capillary column.
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    URL: http://dx.doi.org/10.1007/BF02274512
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    An improved method for determination of light hydrocarbons in stabilized crude oil (1994)
    Springer
    Chromatographia 39 (1994), S. 363-365 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Light hydrocarbons ; Stabilized crude oil ; Capillary guard column
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper reports a quick, and simple method for quantitative determination of C2 to C6 hydrocarbons in stabilized crude oil without using a back flush system. A mixture of crude oil and internal standard is injected into a GC equipped with a 6 meter length of fused silica capillary as a guard column. The light hydrocarbons are separated individually up to the last peak of the hexane group with the heavier components trapped in the guard column. The total analysis time for each sample is 15 minutes. The base line is table for up to 15 consecutive analyses. The guard column and the injector port are then reconditioned by simply heating them for one hour at 300 °C.
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    URL: http://dx.doi.org/10.1007/BF02274526
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    Salt effects in anion exchange displacement chromatography: Comparison of pentosan polysulfate and dextran sulfate displacers (1994)
    Springer
    Chromatographia 39 (1994), S. 409-418 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-exchange chromatography ; Protein purification ; Pentosan polysulfate displacers ; Dextran sulfate displacers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02278755
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    Separation of chlamydosporol epimers by reversed-phase HPLC using commercial solvent optimisation software (1994)
    Springer
    Chromatographia 39 (1994), S. 443-447 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mycotoxins ; Chlamydosporol epimers ; Solvent optimisation ; Fusarium species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02278760
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    Determination of tacrolimus (FK 506) in whole blood using liquid chromatography and fluorescence detection (1994)
    Springer
    Chromatographia 39 (1994), S. 490-496 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Precolumn derivatization ; Dansylhydrazine ; Fluorescence detection ; Tacrolimus (FK 506) in blood
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Spectroscopic studies of butylphenyl, mono-ol and perfluorinated bonded phases (1994)
    Springer
    Chromatographia 39 (1994), S. 520-528 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; New bonded phases ; 13C and29Si CP-MAS NMR ; DRIFT ; ESCA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Analysis of isomers of cholesteryl acetate hydroperoxides by HPLC and GC-ITDMS (1994)
    Springer
    Chromatographia 39 (1994), S. 577-580 
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    ISSN: 1612-1112
    Keywords: Gas chromatography-mass spectrometry ; Column liquid chromatography ; Cholesteryl acetate ; Hydroperoxide formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Retention behavior of aromatic hydrocarbons in reversed-phase liquid chromatography with ion-exchange-induced stationary phases (1994)
    Springer
    Chromatographia 39 (1994), S. 597-601 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-exchange-induced stationary phase ; Retention behavior ; Aromatic hydrocarbons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Graphite layer open tubular (GLOT) columns in gas chromatography and environmental analysis (1994)
    Springer
    Chromatographia 38 (1994), S. 98-108 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid modified adsorption capillary columns ; Polar compound analysis ; Aqueous solution analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The preparation of graphite layer open tubular (GLOT) columns is described together with their application to the analysis of priority pollutants and polar compounds such as alcohols, free carboxylic acids, aliphatic amines and phenols at the sub-nanogram level. A specific application of GLOT columns is for the direct analysis of aqueous solutions avoiding solvent extraction procedures. Several chromatograms of critical separations are reported together with calibration curves. A study of the reproducibility of column preparation is reported in terms of the standard deviation of the capacity ratio and of the minimum HETP obtained.
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    Explanatory coefficients for stationary phases in gas chromatography from McReynolds phase constants (1994)
    Springer
    Chromatographia 38 (1994), S. 679-688 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Stationary phases ; Phase constants ; Explanatory coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Explanatory phase coefficients according to Abraham et al. are calculated from McReynolds index differences and the phase constant B. The retention expression (log Vg)−A=BI/100 connects specific retention volumes and retention indices. McReynolds phase constants and Abrahams explanatory coefficients can be used with similar accuracy for the prediction of relative retention data and for the characterization of stationary phases in gas chromatography. The application of polarity constants for the characterization of stationary phases is discussed.
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    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 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Particle beam MS detection ; Polycyclic aromatic metabolites ; Biodegradation in water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    Improved resolution and determination of ambient C5−C12 hydrocarbons by GC-coupled refocussing system (1994)
    Springer
    Chromatographia 38 (1994), S. 151-157 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; C5−C12 hydrocarbons in air ; Cryogenic focussing ; Thermal desorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A homemade cryogenic system derived from readily available material is described, illustrating its usage as an accessory for adsorption/thermal desorption chromatography. A small Chromsorb-W-HP packing (1 cm) was introduced into a deactivated precolumn as a cryofocussing, preconcentrating unit. This was able to retain the analyte which had been thermally desorpted from a Tenax TA sampling tube at a relatively higher temperature (−80°C∼−90°C), with the analyte also reinjected on the analytical column in a relatively narrow band. Average overall recoveries for 24 hydrocarbons tested were 97.5%. Cryofocussing enhanced sensitivity and improved resolution. Field studies at a petroleum industry site were carried out and the accessory proved to be useful for complex C5−C12 hydrocarbon analysis in ambient air.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290328
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  • 91
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    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
    Keywords: Column liquid chromatography ; Hydrophilic polymer-based packing material ; Direct injection of serum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290333
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  • 92
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    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
    Keywords: Column liquid chromatography ; Nitro-PAHs ; Diesel particulate extract ; Column switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290337
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  • 93
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    A theoretical model of the electron capture detector (1994)
    Springer
    Chromatographia 38 (1994), S. 304-312 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Electron capture detector ; Theoretical model of ECD
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper reports a theoretical model of the ECD detector. The model presented here can be used to examine the influence of pulse parameters on the current and signal characteristics of the detector. On the basis of this model it was found that a space charge is created in the detector when it is supplied with pulse voltage. Due to the electric potential generated by the space charge, in the time between the pulses the electrons and negative ions move towards the detector electrodes. The ionization current of the detector is the sum of the electron current flowing to the anode under the influence of the supplied pulse voltage and the current flowing under the space charge potential in the time between the pulses. It was also found that the detector signal is the sum of the differences between those two currents caused by introducing the sample molecules to the detector. The model was tested for a detector with different electrode configurations which worked at temperature of 300 K or 573 K and which was supplied with nitrogen or Ar+10% CH4 as the carrier gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269772
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  • 94
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    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
    Keywords: Column liquid chromatography ; Liquid crystal phases ; Molecular shape recognition ; Polycyclic aromatic hydrocarbons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269771
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  • 95
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    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
    Keywords: Column liquid chromatography ; In-line derivatization ; Fluorometric determination ; Catecholamines in urine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277159
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  • 96
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    Gas chromatographic separation of isomeric benzene derivatives using molecular sieves, combined with partition columns (1994)
    Springer
    Chromatographia 38 (1994), S. 613-616 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Adsorption and partition columns in series ; Molecular sieves ; Isomers of benzene homologs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The possibility of using short gas chromatographic columns packed with different molecular sieves (silicalite and aluminophosphates), showing definite selectivity to para-isomeric compounds, in series with columns containing a liquid stationary phase was investigated. The molecular sieves were of different origin, while 1,2,3-tris (2-cyanoethoxy)propane (TCEP) and polyethylene glycol adipate (PEGA) were used as the liquid stationary phase. Ortho-, meta- and para-isomers of xylene, chlorotoluene and dichlorobenzene were chromatographed on these columns. It is shown that the best separation is obtained on a combined column with silicalite containing pure silica gel as the molecular sieve, and 10% PEGA as the liquid phase. Molecular sieves of aluminophosphate origin show only weak selectivity toward the para isomers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277163
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  • 97
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    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
    Keywords: Column liquid chromatography ; Glutathione ; Pharmaceuticals and cosmetics ; Pre-chromatographic derivatization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02320453
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  • 98
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    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
    Keywords: Column liquid chromatography ; Reversed-phase systems ; Binary eluents ; Mono-substituted aromatics ; Retention and selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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    URL: http://dx.doi.org/10.1007/BF02320458
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  • 99
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    System peaks in single column ion chromatography (SCIC) with indirect spectrophotometric detection (1994)
    Springer
    Chromatographia 39 (1994), S. 713-718 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; System peaks ; Indirect detection ; Anions and cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274588
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  • 100
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    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
    Keywords: Column liquid chromatography ; Polymeric stationary phase coatings ; PMSC18 ; Column evaluation ; Peak capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274590
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