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  • Column liquid chromatography  (495)
  • Springer  (495)
  • 1990-1994  (495)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 39 (1994), S. 339-345 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; First-guess ; Retention optimization ; Validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A recently reported chromatographic method selection strategy has been validated using fifteen drug formulations selected randomly from the Belgium Compendium, 1992. On the basis of the hydrophobic and the acidic — basic properties of the sample components, reversed-phase was recommended as the first choice mode for all formulations. For two multicomponent formulations the range of analyte polarity dictated the need for gradient elution. The commerical software DryLab G/plus® was used for selection of optimum gradient conditions. The results obtained by both isocratic and gradient chromatography are discussed, as is the usefulness of a tailing suppressor in both modes.
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  • 2
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    Chromatographia 39 (1994), S. 405-408 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrospray mass spectrometry ; Oligonucleotides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Improved HPLC and ESMS conditions have been established, allowing the separation and analysis of oligodesoxyribonucleotides by coupled HPLC-ESMS.
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  • 3
    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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  • 4
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    Chromatographia 39 (1994), S. 427-430 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Microcystins RR and LR ; Solid phase extraction ; Cyano cartridges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method for the determination of microcystins PR and LR in cyanobacterium was developed using cyano-type prepacked cartridges. The microcystins were extracted with 10% acetic acid and the extract applied to a Baker 10 cyano cartridge. After elution from the cartridge with 0.5M acetic acid-acetonitrile (1∶9) the microcystins were determined by HPLC. Better recoveries and chromatograms were observed than with ODS cartridges.
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  • 5
    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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  • 6
    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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  • 7
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Glucocorticoids ; Betamethasone and dexamethasone ; Pharmaceuticals ; Tablet preparations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC method for the simultaneous determination of the glucocorticoids betamethasone and dexamethasone is described. The method based on the separation of these compounds using a binary watertetrahydrofuran mobile phase and a reversed-phase Hypersil C18 column, was applied to the determination of betamethasone and dexamethasone in tablets.
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  • 8
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    Chromatographia 39 (1994), S. 557-563 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Copoly(styrene/methyl 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 methyl methacrylate (MMA) were separated by both normal and reversedphase gradient chromatography. Both modes could be performed by sudden-transition gradients where the polymers were injected into a non-solvent whose polarity was either rather low (e.g.,n-heptane) or high (e.g., acetonitrile). Then the solvent strength of the starting eluent was rapidly increased to a given level by addition of dichloromethane. Under properly defined conditions, the sample components still remained on the column. Elution could be triggered off by the steady addition of another non-solvent whose polarity was opposite of that of the starting non-solvent. Thus, the mixture of five copolymers with MMA content ranging from 14 to 84% could be separated on a polar cyanopropyl column by injection inton-heptane and elution through acetonitrile (normal phase mode) and on a RP C18 column by injection into acetonitrile and elution throughn-heptane (reversed-phase mode), provided that in both modes about 30% dichloromethane was added to the starting non-solvent. The elution sequence in the reversed-phase mode was opposite to that in the normal-phase mode, obeying the approved polarity rules of chromatography in both cases.
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  • 9
    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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  • 10
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    Chromatographia 39 (1994), S. 279-284 
    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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  • 11
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    Chromatographia 39 (1994), S. 285-293 
    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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  • 12
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    Chromatographia 39 (1994), S. 346-354 
    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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  • 13
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    Chromatographia 39 (1994), S. 419-426 
    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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  • 14
    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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  • 15
    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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  • 16
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrodialytic sample treatment ; Computer models ; Analyte enrichment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Basic considerations for analyte enrichment and recovery obtainable by electrodialysis as a sample treatment method are given. Equations are derived which describe the dependence of the concentration profiles of ionic compounds on the electric field strength in a set-up with stagnant donor and acceptor solutions. It is shown that analyte recovery increases when less ion-selective membranes are used in the electrodialysis cell. Computer models are used to estimate the analyte enrichment for a flowing donor (sample) and a stagnant acceptor phase. About 10-fold enrichment can be obtained in an electrodialytic sample treatment system within 20 min under maximum current conditions. A compromise has to be found between analyte recovery and the donor (sample) flow rate.
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  • 17
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Orosomucoid ; α1-acid glycoprotein ; Lipocalin ; Monoclonal antibodies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The accessibility of the surface of human orosomucoid to monoclonal antibodies (MAbs) was investigated by size-exclusion HPLC to examine the validity of its proposed membership in the lipocalin family. The N-terminus half of the molecule contains all the five glycan chains, and of fifty-six MAbs, only one bound to this piece of the polypeptide backbone, indicating that extensive screening was taking place. The simultaneous binding properties of selected MAbs to the fully glycosylated molecule was examined by size exclusion HPLC. The pattern of inhibition was contiguous, with all regions being overlapped. The epitopes of four MAbs having mutual noncompetitive binding were found to be appropriately spaced when placed on a preliminary three dimensional model of orosomucoid. Together, the results support a structure for orosomucoid composed of an exposed continuous protein surface, and a glycan surface screening the remaining protein. Such a structure is provided by the antiparallel β-barrel motif of the lipocalins.
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  • 18
    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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  • 19
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    Chromatographia 39 (1994), S. 577-580 
    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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  • 20
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    Chromatographia 39 (1994), S. 587-590 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; GC-MS ; Thin-layer chromatography ; Essential oils ; Matricaria chamomilla L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Chromatographic methods for qualitative and quantitative analysis of non-volatile and volatile compounds of camomile (Matricaria chamomilla L.) are described. For determination of flavonoids of the apigenin series HPTLC and HPLC were used. To obtain standard samples of components of camomile oil semi-preparative TLC was used. Mass spectra of these standards were obtained to provide a data base. Qualitative and quantitative analysis of camomile oil compounds by GC-MS was then possible.
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  • 21
    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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  • 22
    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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  • 23
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Narrow bore columns ; Cymiazole ; Honey ; Solid-phase extraction ; UV and electrochemical detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC method for determination of cymiazole in honey using a narrow bore C18 column is described. Preconcentration and sample cleaning were achieved by using solid-liquid extraction with SCX Bond Elut cartridges. The performance of UV and amperometric (EC) detector systems were also compared. The detection limits with UV and EC detectors were 1.7 and 0.7 μg kg−1 respectively. Average recoveries obtained with UV and EC detectors were 91.2% and 86.1% with a standard deviation of 3.8% and 12.5% respectively. In spite of its higher sensitivity the EC detector is not suitable for this type of analysis because of its lack of reproducibility and the long analysis time required.
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  • 24
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Column liquid chromatography ; Polycyclic aromatic hydrocarbons ; Environmental samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation in 6 minutes of the sixteen US Environmental Protection Agency (EPA) polycyclic aromatic hydrocarbons (PAHs) on a single packed column by supercritical fluid chromatography (SFC) is described and compared to that obtained using liquid chromatography with the same column. Several environmental samples containing polycyclic aromatic hydrocarbons obtained from various sources including soil, water, petrochemicals and coal have been analysed by SFC under optimised conditions. Packed column SFC is shown to be an efficient and promising method for the rapid monitoring of environmental polycyclic aromatic hydrocarbons.
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  • 25
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    Chromatographia 34 (1992), S. 342-346 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; History of chromatography ; Calcium carbonate stationary phase ; Chlorophyll
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Although Michael Tswett is the originator of chromatography, little is known about the performance of his chromatographic systems. His descriptions of the separation of plant pigments are detailed but nevertheless difficult to interprete by today's chromatographic theory. By our own experiments with the system calcium carbonate/benzene it was found that the separation factor of chlorophyll a and b is approx. 1.6 which means that less than 100 theoretical plates are necessary for separation. Tswett's columns with 50 μm particles and 2–3 cm of bed height presumably exceeded this plate number. His separations could have been impaired by mass overload and by a volume flow rate which was two orders of magnitude faster than the optimum.
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  • 26
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Isomeric substituted alkylbenzenes ; Retention and resolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention data of isomeric xylenes, ethyltoluenes and diethylbenzenes, and of mesitylene, benzene, toluene and ethylbenzene were obtained on a reversedphase column using methanol-water and ethanol-water mobile phases at four different temperatures. This database was used to relate the dependence of solute retention and resolution on the polarity of the mobile phase, solute dipole moment, and column temperature. The additivity of the free energy of the transfer of solute molecules or solute segments from the stationary phase to the mobile phase, was examined for the isomeric compounds. For this, the logarithm of the net retention volume was substituted for the free energy. Deviations from the additivity of free energies indicate that the separation of isomeric substituted alkylbenzenes is governed by their differential interactions with both the polar mobile phase and nonpolar stationary phase. Among the disubstituted alkylbenzenes,ortho-isomers favor the mobile phase more andpara-isomers tend to prefer the stationary phase more. Themeta-isomers are found to follow the additivity rule closely. These trends are amplified as the polarity of the mobile phase is increased indicating that these isomers are resolved better in water-rich mobile phases. These findings are substantiated by analogous results from gas-liquid chromatographic retention data, estimation of dipole moment effects, and examination of the entropic and enthalpic contributions to the net retention volume.
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  • 27
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Column switching ; Polycyclic aromatics ; Oil distillates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A selective and sensitive HPLC method for the determination of Benzo[a]pyrene (B[a]p) in oil fractions by means of column switching is described. The diluted oil samples were injected directly onto a silica column with isooctane as eluent. After fast elution of the main part of the sample matrix, the B[a]p containing fraction was transferred on-line to a dinitro-aryl-modified silica column for final separation with isooctane/tetrahydrofuran. A detection limit of 50 ppt B[a]p was found when using fluorescence detection.
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  • 28
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Molecular recognition ; Multidentate phenyl-bonded phases ; PAHs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary New multidentate phenyl-bonded phases (MPBPs) were synthesized and evaluated the chromatographic retention behaviour with polycyclic aromatic hydrocarbons as sample probes in high-performance liquid chromatography. The new MPBPs show different retention characteristics from the previously synthesized MPBP, designated TP. Nevertheless, the results indicate that the retention mechanism is still the same as the TP phase: the size and shape of the solute molecule can be recognized by a cavity-like space formed by the methyl groups and phenyl rings of MPBPs.
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  • 29
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    Chromatographia 34 (1992), S. 391-397 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Hydrophobic interaction ; Stationary phases ; Salt effect ; Proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention and selectivity in hydrophobic interaction chromatography (HIC) depend both on the type of stationary phase and on the mobile phase. In the last few years various high performance packing materials and columns have been introduced for HIC resulting in a range of different retentions and selectivity. We have investigated the effect of the stationary phase on the retention of various proteins. The retention of some solutes of different hydrophobicities were measured on three commercial HIC columns (TSK-Phenyl, Synchropack-Propyl, CAA-HIC) under isocratic conditions using water-methanol mixtures as eluent. The log kw values determined according to the literature were devalues determined according to the literature were dependent on the type and structure of the stationary phase and indicated a much less hydrophobic character for these columns than that obtained for reversed phase columns. Gradient separations were then carried out on a standard protein mixture using ammonium sulfate and sodium citrate to change the gradient time. In order to compare the effect of the stationary phase and the two salts investigated apparent capacity factors (kg) were determined and plotted against the gradient time obtained for the three columns in the two eluent system. It was shown that the type of stationary phase had a significant effect on the retention of proteins. In addition, the effect of the mobile phase composition, i.e. salt type, was considerably different on the various stationary phases. In order to exploit the potential of HIC to modulate selectivity for the separation of proteins, the combined effect of the stationary phase and the type of salt should be taken into account.
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  • 30
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; PCBs in cod-liver oil ; GC/MS identification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A group of non-planar PCBs (IUPAC nos. 28, 52, 101, 118, 138, 153, and 180) was identified in a cod-liver oil product by using high resolution gas chromatography-mass spectrometry (HRGC/MS) in electron impact (EI) and negative chemical ionization (NCI) modes. The cod-liver oil samples were prepared either in a cyano column by high performance liquid chromatography (HPLC) or by a solid phase extraction (SPE) clean-up procedure that included e.g. purified charcoal treatment. The two methods of sample preparation were evaluated on the basis of the detectabilities of the congeners. The GC/MS-SIM method allowed quantitative monitoring of congeners nos. 52, 101, 118, 138, 153, and 180 at low concentration levels. Detection limits were 1.2 pg and 130 fg (m/z 292.00) in EI and NCI modes, respectively. The determination levels in EI and NCI were 1.8 pg and 290 fg in HPLC followed by HRGC/MS and 170 pg and 27 pg in SPE followed by HRGC/MS. The linear range was from 5.0 pg/μl to 1.0 ng/μl and from 1.0 pg/μl to 1.0 ng/μl in EI and NCI modes, respectively. In addition, the co-planar PCBs, PCDDs, and PCDFs were also screened and two of the chlorinated furanes were identified by HRGC/MS-NCI after separation from non-planar PCBs by SPE. In this case the only congeners that could be quantified were 2,3,4,7,8-PCDF and 1,2,3,4,6,7,8-HCDF, the detection limit for them being 740 fg (m/z 351.90) with NCI. SPE allows the separation of the planar and non-planar compounds, but LC separation is more effective for separation of the compounds of interest from the matrix. LC clean-up is easier and faster to perform than SPE clean-up.
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  • 31
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Flow injection analysis ; Combined methods ; Transition metal ions ; Aqueous samples
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    Topics: Chemistry and Pharmacology
    Notes: Summary An automatic method based on the combination of a flow injection (FI) manifold with a liquid chromatograph has been developed for the enrichment and determination of transition metal ions in water samples. Alternatively, the FI configuration can be used as a screening system for the determination of the total concentration of heavy metals. Two-parameter expressions for calibration graphs involving preconcentration time and concentration of the analytes were established for both the FIA and the integrated FIA/HPLC methods. The preconcentration time depends on the concentration level of the analytes in the samples. The method is linear in the range 2–200 ng/ml, with r.s.d. values between 1.5 and 5.0. It has been applied to the determination of copper, lead, zinc, nickel, cobalt, cadmium and manganese in synthetic water samples.
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  • 32
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Calix[4]arenes ; Host-guest chemistry ; Separation of stereoisomers
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    Topics: Chemistry and Pharmacology
    Notes: Summary A high performance liquid chromatographic procedure on 5 μm RP-18 was developed for the separation of the four possible cis-trans isomers of tetramethyl-calix[4]arenoctol, and of their octaacetates, and their octamethyl ethers.
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  • 33
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Sphingomyelin ; Molecular species separation ; Experimental design and optimization ; Chemometrics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An improved method has been developed for the separation of molecular species of intact sphingomyelins from natural sources (chicken egg yolk, bovine brain, and bovine milk) by high performance liquid chromatography with light-scattering detection. The method was developed and optimized using a novel multivariate optimization strategy.
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  • 34
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    Chromatographia 34 (1992), S. 534-536 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carbohydrates ; Enzymic hydrolysate ; Waste paper
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    Topics: Chemistry and Pharmacology
    Notes: Summary Waste paper was pretreated with 5M sulfuric acid at 28°C to give a gel-like solution which was then hydrolyzed with cellulase, purified fromTrichoderma viride, to form carbohydrates. The determination of the carbohydrates was accomplished using an aminopropylbonded silica HPLC column and an RI detector. The detection limits were 20 ppm; xylose, glucose, and cellobiose were the major components. Salts from the buffer solution may affect the activity of cellulase. The analysis of carbohydrates can be performed under acid conditions. HPLC analysis of carbohydrates from enzymatic hydrolysis is reliable and successful.
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  • 35
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Immunoaffinity chromatography ; Proteins ; Surface plasmon resonance detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The BIAcoreTM Biosensor System utilizes a detection principle known as Surface Plasmon Resonance (SPR) which, in simple terms, detects changes in the refractive index of a solution in contact with a gold film. The gold film is surface modified with carboxymethylated dextran to produce a hydrophillic matrix onto which macromolecules may be covalently immobilized. In this respect, the BIAcoreTM is similar to any other insoluble matrix, such as a chromatographic support. The SPR detection principle, however, allows one to directly ‘visualize’ the interaction under study, in real time and without the need for reporter molecules such as enzyme-labels. In addition, the very small sample requirements, automated robotics unit and ease of data analysis suggest the potential use of the BIAcoreTM instrumentation for assay development and possibly process development, especially where bio-specific interactions such as immunoaffinity chromatography are used as a step in the process. In this report, we demonstrate the use of the BIAcoreTM SPR detector for the micro-scale determination of conditions for immunoaffinity chromatography of soluble complementreceptor 1, sCR1.
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  • 36
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    Chromatographia 35 (1993), S. 5-12 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Post-column reaction detector ; Explosives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Improvements in selectivity and sensitivity in the analysis of common explosives, like nitrate esters, nitramines and nitroaromatic compounds can be achieved by post-column derivatisation in a two step reaction detector. The first step in derivatisation is the photolysis of the analytes with UV at 254 nm. The photo reactor consists of a crocheted 20 m Tefzel capillary, which is coiled around a low pressure mercury lamp. In second step the nitrite ion generated is subsequently detected by a colourimetric reaction. The azo dye formed can be selectively detected at 540 nm. Addition of alkali after chromatographic separation to prevent oxidation of initially formed nitrite to nitrate during photolysis leads to a complex multistage arrangement. However, the contribution to peak broadening by the reactor is negligible and it is possible to detect 25–50 ppb of nitramines and 30–100 ppb of nitrate esters. Another advantage of the method is the selective detection of nitro compounds, even in complex matrices. The trace analysis of explosives is of growing interest in forensic science as well as in environmental analysis. It has been shown [1] that explosives can easily be extracted from soil and debris by the use of supercritical carbon dioxide. The separation and determination of explosives by gas chromatography is hindered by their thermal instability. In HPLC only the nitro aromatic explosives can be detected with sufficient sensitivity. Other types of explosives like the esters of nitric acid or nitramines do not absorb sufficiently in the UV region for sensitive detection. It has been shown [2] that explosives are liable to photochemical decomposition in the UV region, resulting in nitrate and nitrite, which have been detected after separation by ion-pair chromatography with electrochemical detection. A more sensitive and selective detection of nitrite has been possible in flow injection analysis [3]. Here a modified Griess reaction has been used. In a first step nitrite ions are used to form the diazonium salt with sulfanilamide which is coupled in a second step with N-[naphthyl-(1)]-ethylene diamine (NED) to form a redviolet azo dye with an absorption maximum at 540 nm. The advantage of this method is selective detection in the visible region, where hardly any other organic components are detected, which might be present in a crude environmental sample. In this paper the transfer of the Griess reaction to post-column derivatisation in RP chromatography of explosives will be described, and the optimisation of trace analysis of these solutes will be discussed.
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  • 37
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reverse phase ; Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An interpretive optimization procedure in which pH can be one of the variables is presented with the emphasis on optimizing separations. When varying the pH in reversed-phase liquid chromatography the retention of ionogenic solutes will change. Thus, the selectivity between ionogenic and neutral solutes or between ionogenic solutes mutually can be optimized. However, pH also greatly affects the efficiency (plate count) and peak shape (asymmetry). Optimum selectivity (i.e. large differences in retention times) may be observed under conditions where peaks are broad and asymmetrical. Thus, it is essential to simultaneously consider retention, peak width and peak shape and their effects on separation (effective resolution) in pH-optimization studies. A procedure in which this is done is presented and applied to optimizing the separation of a synthetic mixture of selected pharmaceuticals. After initial experiments to establish the parameter space (boundaries for pH and binary methanol — water composition), twelve experiments are performed according to a 3×4 experimental design. At each loaction the retention, peak height, peak area and peak symmetry are recorded for each solute. These data are then used to build models for each of the four characteristics and for each solute. From this set of models the response surface, describing the quality of separation as a function of pH and composition, can be calculated. A variety of optimization criteria (quantifying quality of separation) can be used. The optimum corresponds to the highest point on the response surface.
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  • 38
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    Chromatographia 35 (1993), S. 50-54 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Wine ; Volatile phenols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An alternative to the traditional solvent extraction method used to extract and rapidly quantify ethyl-and vinylphenol and ethyl-and vinylgaiacol from wine is presented. The method is based on retention of volatile phenols on adsorbants. Among the tested resins, the most efficient, AG 2-X8 (anion exchange resin), worked as well with a synthetic solution as with wines. The percolation of clarified wine adjusted to pH 9 on this resin permits, in particular, the elimination of organic acids. Phenols are not eluted after rinsing the column with 1N HCl, but are eluted with methanol after this treatment. Good recovery (91 %) and good repeatability are observed. The eluate is directly analysed by HPLC on an RP18 column after two-fold dilution in water. The four volatile phenols were completely separated and detected by UV at 280 nm with high sensitivity (20–40 ppb). No interference with other compounds were noted in the different wines analysed.
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  • 39
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    Chromatographia 35 (1993), S. 90-92 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; α1-acid glycoprotein ; Complex glycans ; Allergic reaction ; Terfenadine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Little is known about the alterations that have occurred at the individual glycosylation sites in allergy patients or how these glycosylation patterns may change after anti-allergy treatments. Using reverse-phase HPLC, we have quantitated the glycoforms present at the individual glycosylation sites on orosomucoid isolated from the sera of allergic reaction patients and an allergic reaction patient treated with the antihistamine Terfenadine. The glycan structures isolated from the five glycosylation sites for the individual taking Terfenadine were all within normal ranges. It is suggested that if the changes in glycosylation in OMD in the allergic state are functionally driven, then it should be possible to correlate biological activities with quantitative changes at the individual glycosylation sites, and hence further define the role of OMD in allergy and inflammation.
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  • 40
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Bonded liquid crystals ; Polymeric stationary phases ; Variable temperature studies
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    Topics: Chemistry and Pharmacology
    Notes: Summary Using two polycyclyic aromatic hydrocarbons as solutes, a comparison is made between a bonded liquid crystal stationary phase and a conventional polymeric C-18 phase. The bonded nematic liquid crystal phase was the silanized form of 4-[4-(allyloxy)benzoyl-oxy]biphenyl and the polymeric phase was Vydac 201TP. Both phases display shape and planarity selectivity as indicated by the results of the variable temperature and mobile phase composition studies. The slot theory of retention can be used to explain these results. However, the liquid crystal phase is more sensitive to molecular geometry, probably due to its more ordered structure on the surface. Variable temperature experiments which compare retention during both heating and cooling provides additional support for this conclusion. With the polymeric bonded C-18 phase, each solute had identical retention at the same temperature during both the heating and cooling cycles. On the bonded liquid crystal phase, measurable differences in retention were observed at identical temperatures depending on whether the column was heated or cooled. This effect is attributed to a degree of partially reversible disordering which occurs as the column temperature was increased. However, conditioning with the appropriate mobile phase can restore the original retention characteristics of the bonded liquid crystal phase.
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  • 41
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Pre-column derivatisation ; Morpholine and degradation products ; Boiler feed water
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    Topics: Chemistry and Pharmacology
    Notes: Summary Morpholine and its amine-type thermal degradation products present in boiler feed water and steam condensate were derivatised with N-succinimidyl-p-nitrophenylacetate. These pre-column derivatives were determined by high-performance liquid chromatography with UV detection at 280 nm. The analytical column was Supelco-sil-ODS with an isocratic mobile phase. Morpholine and its breakdown products were monitored in the range 0.01–10 μg ml−1 with a relative standard deviation of 0.4–3.0%. Chromatographic analysis of boiler feed water and steam condensate samples collected from a boiler servicing a petroleum refinery is described.
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  • 42
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    Chromatographia 35 (1993), S. 264-268 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomer separation ; Stereospecific synthesis ; Crown ether phase ; Immobilized enzyme reactor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A prototype of a coupled-column chromatographic system has been developed to determine the enantiomeric purity of enzymatically produced chiral compounds. In this system, an immobilized enzyme HPLC reactor based upon α-chymotrypsin (ACHT-IMER) was linked through a switching valve to a chromatographic column containing a crown ether-based chiral stationary phase (CR-CSP). Although ACHT is normally stereospecific for the L-enantiomorphs of aromatic amino acids, L-tryptophan (L-TRP), L-tyrosine and L-phenylalanine, we were able to achieve the hydrolysis of D-TRP methyl and ethyl esters on the ACHT-IMER. The percent of hydrolysis of the D-TRP esters could be manipulated by varying the resident time in the ACHT-IMER. In a series of experiments, D,L-TRP methyl or ethyl esters were injected into the ACHT-IMER, the flow stopped and after resuming the flow, the eluent which contained the hydrolyzed aminoacids, D- and L-TRP, was switched onto the CR-CSP where the enantiomeric composition of the TRP peak was determined. This configuration is a model for other IMER/CSP coupled-column systems which can be used for analytical and preparative applications.
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  • 43
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    Chromatographia 35 (1993), S. 295-301 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Used column packings ; Particle size distribution ; Scanning electron microscopy ; Column age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Particle size distribution analysis and scanning electron microscopy (SEM) were carried out on eight used HPLC columns containing either irregular silica based, spherical silica based or spherical polymer based packing material. Particle size distributions of the used irregular silica based columns were at least bimodat at the outlet ends and either biomodal or log-normal at the inlet ends with regular progressions between the two extremes through the column. A new ODS-3 column showed log-normal size distributions from the inlet to the outlet ends. Spherical silica based column particle size distributions showed distinct shoulders on large central distribution peaks in most column sections with various degrees of shoulder erosion. The spherical resin based column showed a broader inlet particle size distribution progressing to a very narrow outlet distribution. SEMs of both irregular and spherical silica based columns revealed a larger number of undersized particles and debris at the outlet than inlet ends which could have resulted from stationary phase degradation, since this was not seen in the new ODS-3 column. While several SEMs of the spherical silica based columns revealed hollow spheres and twins, the spherical resin based column packing showed stress fractures or wrinkle lines resulting from use or dehydration.
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  • 44
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomer separation ; Chiral ovomucoid column ; Diltiazem hydrochloride ; Clentiazem maleate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A direct HPLC separation method was developed for the determination of the enantiomers of racemic precursors to diltiazem (I) and its 8-chloro derivatives (II). The enantiomers were successfully separated on a chiral ovomucoid column using an aqueous-organic mobile phase (reversed-phase HPLC). The influence of the organic modifier and buffer pH on the retention and enantioselectivity was investigated. The chromatographic conditions chosen for the separation permitted complete resolution of the enantiomers of both the acid (Ib and IIb) and methyl ester precursors (Ia and IIa) within 20 min. The influence of sample load on retention times, theoretical plates numbers, peak heights and peak areas was also investigated. The peak areas showed a good linearity over the concentration range examined, although all the others were influenced significantly by the sample size. An optical antipode of the intermediate to be determined could be detected by the area-percentage method down to ca. 0.1%, together with the determination of its precursor, including its optical purity.
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  • 45
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Probenecid in urine ; Solid-phase extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This study describes a rapid method for the determination of probenecid in human urine by liquid chromatography with UV detection at 254 nm, after clean-up through a C8 solid-phase extraction column. Liquid chromatography was carried out on a C18-bonded phase using an acetonitrile-acetate buffer (pH=4) gradient elution. Ethacrynic acid was used as internal standard. The system has been applied to the determination of probenecid in the 0.10–100.0 μg/ml concentration range; the limit of detection was 5 ng/mL.
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  • 46
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    Chromatographia 35 (1993), S. 387-389 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Buffer composition effect ; Agarose ; Albumin ; Ionic adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The adsorption of albumin on a commercial, high quality agarose (Sepharose® 6B) was studied in different buffers of low pH (4.00) and low molarity (9–11 mM). Eluents containing 0.025% albumin were introduced onto small gel columns until saturation and the adsorption capacity of the gel in different buffers calculated. Adsorption was high in solutions of monobasic acids. Although cation-exchange interactions between the protein and the gel matrix were found to be influenced essentially by the sodium ion concentration or ionic strength of the buffer, adsorption in cirate buffers is weak compared to that in formate, acetate or propionate buffers of about the same ionic strength (I=0.01).
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  • 47
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyunsaturated fatty acids ; Direct injection ; Enthalpy of adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention studies on arachidonic acid 5, 8, 11, 14 all cis eicosatetraenoic acid, C20:4ω6), eicosapentaenoic acid (5, 8, 11, 14, 17 all cis eicosapentaenoic acid, C20∶5ω3) and docosahexaenoic acid (4, 7, 10, 13, 16, 19 all cis docosahexaenoic acid C22∶6ω3) were performed on a commercial μBondapak free fatty acid analysis column. The ternary mobile phase consisting of acetonitrile, water and tetrahydrofuran was used in an isocratic mode with differential refractometry detection. Retention data were mesured at various flow rates with two different, mobile-phase compositions. Capacity factors and enthalpy of adsorption were calculated from the retention data. Finally the retention mechanism is explained.
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  • 48
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    Chromatographia 35 (1993), S. 439-447 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Affinity chromatography ; Polythiolpeptides and metallopolythiolpeptides ; Mechanism of separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Covalent affinity chromatography with thiol-disulphide interchange (CAD-TDI) is a method for the separation of thiolproteins based on the interaction between disulphide bridges immobilised on a insoluble support and thiol groups in the protein undergoing separation. Mercury-thionein, cadmium-thionein and apothionein have been used as low molcular weight thiolproteins rich in cysteine residue. The proposed separation mechanism is more complex than those in the literature and can have anionic, cationic or a free radical character depending on the protein, the ligand and the conditions during separation.
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  • 49
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Adenine ; Monoamino analogues of dideoxyadenosine
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    Topics: Chemistry and Pharmacology
    Notes: Summary A liquid chromatographic method that can separate each of the monoamino analogues of dideoxyadenosine and 9-(-dideoxy-β-D-lyxo-pentofuranosyl)adenine from their main degradation product, adenine, is described. The influence of the pH of the mobile phase, the type and concentration of the organic modifier and the concentration of the silanol masking agent and the buffer have been investigated. Several reversed phases were examined. Samples were finally analyzed on a 10 μm Spherisorb ODS1 column (250 mm×4.6 mm I.D.) using acetonitrile −0.2 M potassium phosphate buffer pH 6.0–0.2 M tetramethylammonium phosphate pH 6.0-water (5∶5∶0.5∶89.5, v/v) as the mobile phase. The interactions between the solute and the stationary phase are discussed in view of the basic properties of the compounds under study.
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  • 50
    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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  • 51
    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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  • 52
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    Chromatographia 39 (1994), S. 155-161 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemically bonded phase (CBP) ; Alkylamide phase ; Surface characterization ; Thermal stability ; Packings evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A series of chemically bonded phases has been prepared with amide groups localized by means of hydrophobic ligands. The physicochemical and chromatographic properties of such phases with chain lengths ranging from C5 to C8 have been examined by porosimetry, elemental analysis, solid-state NMR, and liquid chromatography. Subsequently, the conformational dynamics of these phases have been investigated by analyzing the dependence of the capacity factor (k) on the reciprocal of temperature for different organic compounds. Special emphasis has been given to the reproducibility of retention data obtained before and after temperature-dependent measurements.
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  • 53
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; N-nitrosamines ; Fluorescent derivatives ; Luminarin 9 ; Precolumn derivatization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive precolumn fluorescence derivatization method for low level detection of the, volatile (N-nitrosodimethylamine and N-nitrosopyrrolidine) and non-volatile N-nitrosamines (N-nitrosoproline and N-nitrosodiethanolamine) an high-performance liquid chromatography was developed. This method is based on the denitrosation of the compounds of interest by a mixture of hydrobromic acid and acetic acid to produce the corresponding secondary amines. These are, then, able to react with, a quinolizinocoumarin derivative (luminarin 9®) to form highly fluorescent labelled N-nitrosamine derivatives. The structural elucidation of the luminarin 9® derivatives of N-nitrosoproline and N-nitrosodimethylamine by way of example, were established by liquid chromatography-mass spectrometry (LC-MS) and by direct chemical ionization-mass spectrometry (CI-MS). The separation, derivatization and detection conditioins were optimized for all the studied compounds. The detection limits (signal to noise ratio=3) were between 0.4 and 1.0 pmol injected depending on the compound. The calibration graphs were linear for derivatized amounts in the range of 0.5–40 nmol for N-nitrosodimethylamine and N-nitrosopyrrolidine, 0.4–2- nmol for N-nitrosoproline and 1.0–40 nmol for N-nitrosodiethanolamine. The repeatability (RSD less than 3.5%, n=6) and reproducibility (RSD less than 4.8%, n-6) were satisfactory.
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  • 54
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    Chromatographia 39 (1994), S. 216-223 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gradient elution ; Optimization of gradients ; Ternary solvent mobile phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this work, an optimization procedure for gradient RPLC separation, using ternary mobile phases, is described. This procedure requires eight preliminary experiments in gradient elution mode to predict the retention surface for each solute over the whole triangular space. This is followed by computerized calculations to determine the best ternary gradient elution profile with respect to both selectivity and analysis time. The efficiency of this procedure from the point of view of rapidity and of accuracy, is illustrated for the specific separation of twelve phenyl urea herbicides.
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  • 55
    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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  • 56
    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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  • 57
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    Chromatographia 39 (1994), S. 246-248 
    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.
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  • 58
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polystyrene ; Ethyl acetate ; Dichloromethane
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    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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  • 59
    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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  • 60
    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).
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  • 61
    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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  • 62
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral separation ; Amphetamine ; Cyclodextrin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The enantioseparation of amphetamine, methamphetamine and various ring-substituted amphetamines by use of a chiral stationary phase carrying immobilized native β-cyclodextrin (β-CyD) selectors is reported. The system is evaluated for resolving the specified compounds directly without any derivatization and after derivatization with phenyl isothiocyanate (PITC), naphthyl isothiocyanate (NITC) and 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC). This direct enantioseparation is compared with the features of indirect separation of diasteromeric derivatives after reaction with the optically pure Marfey's reagent employing a simple non-chiral alkyl-silica (RP-8) column. A selection of those methods best suited for each single amphetamine is given. Seventeen different samples of amphetamine, confiscated by the Swedisch police, were analyzed with respect to their enantiomeric composition. Within this set of samples synthesized by the same method no significant deviation from a racemic ratio could be observed.
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  • 63
    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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  • 64
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Peptide characterization ; Thiol groups ; Electrochemical detection ; Metallothionein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The hexapeptide Lys-Cys-Thr-Cys-Cys-Ala [56–61] MT I is a molecule intrinsic to the metallothionein structure. Its chromatographic behaviour on a reversed-phase column, using electrochemical detection has been studied in order to get a better understanding of its chemical stability under various conditions. The chromatogram of the peptide consists of two peaks. The optimization procedure for their separation is presented and a hydrodynamic voltammogram has been generated. The relative proportion of the two peaks can vary with experimental conditions and is clearly dependent of the peptide concentration. Following the various experiments to which the peptide was submitted, namely elution after air oxidation, under inert atmosphere, in basic pH, after addition of an oxidizing agent (H2O2) and after addition of a reducing agent (2-mercaptoethanol), a reaction scheme was suggested: transformations of the reduced hexapeptide (three free thiol groups) into—as a first step—its intramolecular oxidized form (one SS bond, one free SH) and then into—as a second step—the fully oxidized dimeric form (no more free SH). Electrochemical detection allows a quantitative follow-up of the thiol oxidation and hence, of the disappearance of the reduced peptide.
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  • 65
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Column switching ; Columns at different temperatures ; Polycyclic aromatic hydrocarbons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple and efficient method of separating a 20-component PAH-mixture (RSM 1647 standard mixture +benzene, toluene, perylene and coronene) by RP-HPLC is described. Separation was by using two Superspher-100 RP-18 cartridges thermostatted at different temperatures under isocratic conditions with water-acetonitrile eluent. The analysis time with complete resolution of all components can be reduced to 15 min.
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  • 66
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Copoly(styrene/ethyl methacrylate) ; Gradient elution ; Precipitation chromatography of polymers ; Solubility of polymers
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    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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  • 67
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    Chromatographia 39 (1994), S. 107-109 
    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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  • 68
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    Chromatographia 39 (1994), S. 713-718 
    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.
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  • 69
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    Chromatographia 39 (1994), S. 740-742 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous graphitized carbon ; Taxol ; Taxus baccata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Porous graphitized carbon columns have been used for the separation and quantitative determination of the anticancer drug taxol in the bark and foliage ofTaxus baccata. Successful separations were achieved using water∶dioxane 54∶46 v/v eluent. Peak purity tests and the spectra of taxol peaks taken at different retention times indicated that the taxol peak is not entirely homogeneous and probably contains other taxoteres coeluted with the main compound.
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  • 70
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chlorophyll c pigments ; Chromophyte algae ; Monomeric and polymeric ODS phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Photosynthetic pigments from chromophyte marine algae were analyzed using three different commercial columns with ODS stationary phases of different degrees of polymerization. No separation of chlorophylls c1 and c2 could be achieved using monomeric or intermediate stationary phases, even at subambient temperatures. As with other planar compounds, the polymeric stationary phase showed the highest selectivity for chlorophyll c pigments, allowing the simultaneous separation of chlorophylls c3, c1 and c2 and other pigments occurring in chromophyte algae by using a binary gradient starting with a highly buffered mobile phase.
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  • 71
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    Chromatographia 35 (1993), S. 548-554 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyaromatic ester copolymer phases ; Polymer phases with C8 and C18 alkyl chains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The Friedel-Crafts reaction has been used for chemical modification of a highly cross-linked di(methacryloyloxymethyl)naphthalene-divinylbenzene copolymer and the influence of the chemical modification on the chromatographic behaviour of the copolymer has been studied. The capacity factors and retention indices of five homologous series and test compounds were different on columns packed with modified and unmodified copolymers: the order of elution of the test compounds was indicative of significant differences between these and the unmodified copolymer. The porous structure of the modified copolymers was also observed to be different from that of the unmodified material.
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  • 72
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    Chromatographia 35 (1993), S. 555-559 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cyclodextrin-bonded phase ; Optical resolution ; Uniconazole inclusion complex ; Nuclear magnetic resonance spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Enantiomers of uniconazole have been separated by high-performance liquid chromatography on a γ-cyclodextrin-bonded column and the mechanisms of the chiral recognition have been studied. From investigations on the retention and resolution of structurally related compounds of uniconazole on γ-and β-cyclodextrin columns the benzene ring and alkyl group of the solute were found to play an important role in the formation of the CD complex and in the chiral recognition. Nuclear magnetic resonance data for the model systems of uniconazole and some analogs also supported these conclusions.
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  • 73
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    Chromatographia 36 (1993), S. 53-56 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Urinary organic acids ; Creatinine ; Aromatic solvents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A high-performance liquid chromatographic method for the simultaneous determination of urinary organic acids and creatinine for following the metabolism of aromatic solvents is reported. After extraction of acidified, filtered urine with diethylether followed by evaporation, the dried residue is dissolved in mobile phase. Hydroxybenzoic acid is used as internal standard. A column of Nucleosil C18 is used with a precolumn of the same material. The mobile phase is acetonitrilephosphate buffer, pH 3.3 (17∶83). For determination of creatinine the sample is simply diluted 10-fold and the eluate monitored at 215 nm (UV). This technique gives highly reproducible results and is simple, reliable and useful for biological monitoring.
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  • 74
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Nitrites ; Fluorescence ; Precolumn derivatization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid, simple, and sensitive method is described for determination of nitrites in water. Nitrite (NO2−) ions react with coumarin 120® (4-methyl-7-aminocoumarin) in sulfuric acid medium to give the corresponding 7-diazo compound. After hydrolysis, this latter yields (95%) the highly fluorescent 4-methyl-7-hydroxycoumarin (4-methylumbelliferone) which is fluorimetrically detected at 380 nm after excitation at 325 nm. In order to avoid interference from both excess coumarin 120® and the trace amounts of 4-methylumbelliferone which occurs in coumarin 120® as an impurity, use of HPLC is mandatory; a satisfactory separation is obtained on a cyano stationary phase with apolar hexane-isopropanol (95∶5, v/v) as eluent. Under these conditions, linearity of response is obtained from 1 to 30 μg.L−1 of NO2−; the limit of detection is 0.5 μg.L−1. The repeatability and reproducibility, expressed as RSD %, are 2.5 and 4.7 % respectively, for n=6 and 5 μg.L−, analytical characteristics which demonstrate the reliability of the proposed method.
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  • 75
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Argentation thin-layer chromatography ; Solid phase extraction ; Fatty acid hydroperoxides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Studies of lipid oxidation usually employ such model systems as purified fatty-acid methyl ester. While methyl oleate hydroperoxides (MOPHs) can only be readily separated from the matrix by HPLC, because of their heat-susceptibility and relative instability, these same techniques are unable to separatecis MOHP fromtrans isomers. The present study reports an enhanced, rapid separation method forcis andtrans isomers of methyl oleate hydroxides, as well as HPLC determination of positional isomers per fraction of configuration isomer and isomer identification by gas chromatography-mass spectrometry.
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  • 76
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carbonyl compounds ; Luminarin hydrazides ; Fluorescence detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Fluorogenic reagents (luminarin 3, luminarin 11 and luminarin 12), having a quinolizinocoumarin moiety as fluorophore and a carboxylic acid hydrazide function as reacting group, have been developed. These reagents were found to be highly sensitive fluorescence derivatization reagents for aldehydes and ketones in high-performance liquid chromatography. The reagents readily react with carbonyl compounds in aqueous sulphuric acid solution (0.1 M) at room temperature to produce the corresponding hydrazone derivatives, which can be separated on both reversed or normal-phase column. The structures of the derivatives were studied, together with their properties in reversed and normalphase chromatographic systems. UV absorbance, corrected fluorescence spectral data and quantum yields of luminarin 3, luminarin 11 and luminarin 12 are presented. The detection limits (signal to noise ratio=3) for aldehydes and ketones were in the sub-pmol range. Luminarin 3 was also applied to the determination of hydroxymethylfurfural (HMF) in orange juices and concentrates. The method for HMF involves the solid-liquid extraction of the juice by using a C-18 cartridge prior to derivatization and normal-phase separation of the derivative with fluorimetric detection at 387 nmex., 444 nm em. The calibration curve was linear for amounts of HMF ranging from 0.1 to 10 nmol. Intrarun relative standard deviation was 12.8% for 0.1 nmol and 2.6% for 1 nmol. Recovery studies indicated an average of 98.7±1.9% for juice concentrate and 99.8±3.2% for pasteurized juice.
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  • 77
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Glutathione ; o-Phthalaldehyde ; Post-column derivatization ; Plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for the assay of various forms of glutathione in human plasma has been developed. The reduced form was measured after direct injection of deproteinized plasma with perchloric acid. The unbound oxidized forms were assayed in deproteinized plasma after reduction with dithiothreitol. The total amount of glutathione was determined by reduction before protein precipitation. Separation of reduced glutathione from other endogenous thiols was by ion-pair, reversed-phase, high-performance liquid chromatography. Post-column derivatization withortho-phthalaldehyde made the assay more selective than when using pyrenemaleimide as thiol fluorogenic reagent. The linear range was 0.02 to 2.0 μg mL−1 with good repeatability (relative standard deviation less than 5% for the lowest concentration measured).
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  • 78
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Plastics additives ; Optimization ; Elution gradient ; Light-scattering detector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of two families of plastics additives (phenolic antioxidants and UV absorbers) has been achieved by high performance liquid chromatography with a quaternary gradient. A methodology of separation based on a sequential optimization is described. After a preliminary study of the effects of solvents on retention of compounds, the mobile phase is first chosen for each class of additives (Irganox and Tinuvin), then for the mixture of all the compounds and the separation is finally optimized. The importance of the column phase ratio is also reported. The use of two detectors, UV absorbance and light-scattering, enables all the compounds to be detected. The performance of the detectors has been compared and the effects of the nebulization temperature on the detection of low molecular mass compounds is reported.
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  • 79
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    Chromatographia 36 (1993), S. 147-151 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polarity ; Retinoids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention of retinoids in reversed-phase liquid chromatography was studied using aqueous mobile phases of different composition (methanol 94–86% and acetonityrile 92–82%) at five temperatures (40–60 °C). With both organic modifiers the effect of the molecular structure increased as the water content and the polarity of the mobile phase increased. The temperature-dependence increased in the same manner with aqueous acetonitrile mobile phases. The π-π interactions between the retinoids and acetonitrile diminish when the water content of the mobile phase is increased, as happens also to the hydrophobic interactions with both organic modifiers. The net effect of these changes depends on the composition of the mobile phase. There was excellent correlation of retention with all polarity parameters studied(ϕ, P′, xe, xd, xn, E T N , δT, δ, δo and δd), when the calculations were made separately with methanol and acetonitrile. The volume fraction of the organic modifier, ϕ, was the only parameter describing the retention well in both organic modifiers simultaneously.
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  • 80
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Photodiode array detection ; Chlorophylls ; Pheophytins ; Drying ; Mint (Mentha spicata Huds.) ; Basil (Ocimum basilicum)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of drying conditions on the preservation of chlorophyll pigments in mint and basil have been investigated in order to determine the effects of drying temperature and whether or not there was a prior blanching. Pigments extracted from fresh and dried samples were analyzed by reversed phase high performance liquid chromatography coupled to a photodiode array detector; isocratic separation was performed on a Zorbax ODS C18 column. The purity of the chromatographic peaks of chlorophylls and breakdown products was investigated. The visible spectra of standard samples of chlorophylls and pheophytins were compared, using least squares normalization with those of peaks from the extracts of fresh and dried mint and basil. The study has shown that chlorophylls were better preserved when drying was preceded by a short blanching; if samples were not blanched before drying, the degradation of chlorophylls a and b was best prevented by drying at low temperatures.
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  • 81
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Binary solvent systems ; Cyclodextrin and modified Cyclodextrin ; Solubility ; Hydrophoby
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In the course of systematic studies on the solubility, hydrophobicity and complexation properties of cyclodextrins and modified cyclodextrins, the retention behavior of α, β, γ and of some glycosylated cyclodextrins has been examined by means of reverse phase HPLC. Mobile phase mixtures containing large amounts of water have been used because of the possible application of such systems to biological studies. Mobile phase mixtures with both methanol and acetonitrile show a linear relationship between the volume fraction of the organic part of the mobile phase and the logarithm of the capacity factor. The extrapolation of capacity factors to a total aquous system are used and compared to other techniques (including solubility) in order to evaluate the hydrophobic properties of the cyclodextrins. In particular, the solubility of cyclodextrins has been explored for a wide range of organic solvent/water mixtures. Whilst β cyclodextrins are definitely the most hydrophobic, followed by glycosylated β cyclodextrins, the others behave differently in the two mobile phase systems. The differences observed in the results are related to the chemical nature of the organic phase. Comparisons between chromatographic and solubility methods are given and interpretations are proposed. Some cyclodextrins have been modified to increase or modify not only the hydrophobicity but also the solubility, the complexation and the molecular recognition of drugs. The most important aim of this study was to define conditions and rules for further drug vectorization by cyclodextrin-drug complexation.
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  • 82
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    Chromatographia 36 (1993), S. 347-350 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Allium ; Derivatization ; S-alk(en)yl-L-cysteine sulfoxides ; Sulfur amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two pre-column derivatization procedures coupled with reversed phase HPLC have been compared for the analysis ofS-Alk(en)yl0L-cysteine sulfoxides in variousAllium species. In order to establish external standards some (+/-) sulfoxides were synthesized, using a new method to enhance asymmetric synthesis of the diastereoisomers. The first derivatization method is the formation ofo-phthaldialdehyde/tert.-butylthiol derivatives which can be analyzed using UV detection. The second, presently used for amino acid analysis, is the Waters Pico-Tag method, which employs phenylisothiocyanate as derivatization reagent. As the Pico-Tag method was found to be the most efficient for determination ofS-alk(en)yl-L-cysteine sulfoxides it was used to determine the alliin content of various samples of garlic.
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  • 83
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Anion-exchange chromatography ; Carbohydrates ; Monosaccharides ; Oligosaccharides ; Sugars ; Pulsed amperometric detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High performance anion-exchange chromatography (HPAC) coupled with pulsed amperometric detection (PAD) under alkaline conditions (pH 13) separates neutral saccharides based upon their molecular size, saccharide composition, and glycosidic linkages. Carbohydrates were detected by oxidation with a gold-working electrode. HPAC-PAD was compared to high performance liquid chromatography (HPLC) with refractive index (RI) detection in terms of selectivity and sensitivity of saccharides. The results indicate that HPAC-PAD was more precise, two orders of magnitude more sensitive (pmol range) and gives better resolution of saccharides than HPLC-RI. HPAC-PAD required less sample preparation and was not subjected to matrix interferences. The use of HPAC-PAD was applied to the analysis of organic materials (plant residues, animal wastes and sewage sludge) and soil.
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  • 84
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Extraction cartridges ; Erythromycin ; Josamycin ; Serum and urine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The re-usability of C18 solid-phase extraction (SPE) cartidges was assessed utilizing two different analytical procedures developed for the analysis of erythromycin and josamycin in human serum and urine. A statistical procedure using confidence intervals was employed in order to determine a 10% change in drug recovery on re-use with a 95% degree of certainty. The results obtained indicated that the SPE cartridges could be successfully re-used up to three times for serum and urine samples containing physiological concentrations of erythromycin base and propionate. However, in the case of josamycin, results were inconsistent after the second re-use of the extraction cartridges for serum samples. Reproducible results, however, were still obtained for urine samples using the same SPE cartridges up to four times. The results indicate that although succesful re-use of SPE cartridges is possible, each drug and associated extraction conditions need to be carefully assessed prior to implementing such re-use.
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  • 85
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    Chromatographia 29 (1990), S. 51-53 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrochemical detection ; Amino acid enantiomers ; OPA-TATG ; Fruit juices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A fast and simple HPLC-method for the determination of synthetic amino acids in adulterated orange juice has been developed. The amino acid enantiomers were derivatized with a chiral reagent and the derivatives separated on a 3 μm particle size C18 column. An electrochemical detector operating in the oxidative mode was used for detection. The potential at which the derivatives are oxidized was determined by cyclic voltammetry. By using selective (electrochemical) detection it is possible to reduce the sample clean-up to simple centrifugation and filtration steps.
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  • 86
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin layer chromatography ; Azidothymidine ; Thymine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary HPTLC densitometry and HPLC are considered for the determination of azidothymidine and its degradation product thymine in pharmaceutical dosage forms. In HPTLC the substances were separated on silica gel with fluorescence indicator in methanol-chloroform (10∶90) and methanol-chloroform (15∶85) systems. Absorbance measurement (detection of reflectance) of the separated substances was carried outin situ at 268 nm using four-level calibration (external standard, linear regression function) in the concentration range of 25–100 ng thymine/spot and using single-level calibration (external standard) at the concentration of 100 ng azidothymidine/spot. HPLC was carried out using RP-18 stationary phase and methanol+aqueous 0.03 mol/l KH2PO4 (18+82, v/v) as the mobile phase. The temperature was 50°C and the detection wavelength 266 nm. The detection limit of thymidine was 0.05%. The concentration range for azidothymidine was 0.5–1.5 mg/ml and for thymine 1–40 μg/ml (for an injection volume of 10 μl). The results were evaluated by linear regression analysis.
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  • 87
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    Chromatographia 29 (1990), S. 530-536 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reversed phase gel permeation-coupling ; Polyethyleneglycol in surfactants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Quantitative HPLC methods for substances that elute in the vicinity of the V0 peak are often characterized by poor reproducibility and/or serious systematic errors. This contribution shows that the problem can be solved when a GPC-column is coupled with the HPLC-column; the substances assembled in the V0-Peak are developed into a new dimension (Retention volumes become shorter than V0) und thus a separation from the V0 zone is achieved. The method is used to determine polyglycol in aliphatic and aromatic nonionic surfactants with a degree of ethoxylation up to 80. The products have to be soluble in methanol/water in the proportions 80/20. Polyglycols with a molecular weight up to 7000 are separated by gel chromatography according to their degree of ethoxylation, so that the mean molecular weights (number and weight average) are additionally accessible. It is found that the degree of ethoxylation in polyethyleneglycol is greater than in the associated surfactant.
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  • 88
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cation-exchange chromatography ; Organic acids, sugars and alcohol ; Cocoa beans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A cation-exchange HPLC column was evaluated for the analysis of sugars (sucrose, glucose, fructose), acids (citric, lactic and acetic) and ethanol in extracts of cocoa, preserved in a solution of benzoic acid (0,2 % w/v). Optimum sensitivity, precision and selectivity was achieved when the column was operated at a temperature of 25 °C and the combination of a refractive index detector and peak height measured peaks was employed. The limit of detection was 3.5 ng acetic acid, 5.5 ng sucrose, 6.3 ng fructose and lactic acid, 7.3 ng citric acid, 10.5 ng glucose and 12.4 ng ethanol. The extracts of cocoa were stable over a 10 week period, permitting the analysis of large numbers of samples without degradation of the analytes.
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  • 89
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Structure-retention relationships ; Mathematical data analysis ; Phenol derivatives ; ODS and graphitized carbon columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention of 22 ring-substituted phenol derivatives on porous graphitized carbon (PGC) (eluents: acetonitrile — water and methanol — water mixtures) and on octadecylsilica (ODS) (eluents: methanol — 0.025 M KH2PO4 mixtures) was determined, and the relationship between retention and physicochemical parameters were evaluated by principal component analysis followed by two-dimensional nonlinear mapping and by cluster analysis as well as by canonical correlation analysis. Calculations proved that marked differences can be detected between the retention characteristics of PGC and ODS columns, and the electronic parameters of phenol derivatives have the highest impact on their retention. The comparison of various multivariate mathematical-statistical methods indicated that principal component analysis followed by two dimensional non-linear mapping is the most appropriate method for the evaluation of large data matrices in RP-HPLC.
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  • 90
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Lamotrigine ; Antiepileptics ; Plasma ; Liquid extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The concurrent administration of several antiepileptic drugs for the treatment of seizure disorders has become common practice. Lamotrigine is a new antiepileptic given in combination with other antiepileptic drugs, but which is not routinely measured in clinical laboratories. An isocratic high-performance liquid chromatographic method is described for the simultaneous measuring lamotrigine, carbamazepine, phenobarbital and phenytoin within 10 minutes. The chromatographic system used an Hichrom Spherisorb CN column (20 cm×4 mm, i.d., 5 μm particle size), a μBondapak CN precolumn, and a mobile phase consisting of methanol : acetonitrile : 5 mM sodium acetate (5:20:75: by volume, pH adjusted to 6.3 with acetic acid). BWA 725C was used as internal standard. The drugs were extracted from 200 μl of plasma with ethyl acetate, acetonitrile and 5 mM sodium acetate. After evaporation of the organic layer and reconstitution in mobile phase, 25 μl of extract was eluted with mobile phase at a flow rate of 1.2 ml/min. The eluted drugs were detected by their absorption at 205 nm and quantified from their peak heights. The method was found to be rapid, relatively simple to perform and sufficiently sensitive to determine each drug over its entire therapeutic range. Lower limits of detection varied from 50–100 ng/ml, absolute recoveries from 93–98%, and mean intra- and inter-assay CVs were 〈3.0%.
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  • 91
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Prostaglandins ; C18 Solid phase extraction ; Radioimmunoanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The aim of this study has been the evaluation of an automated system for on-line sample preparation using solid phase extraction and HPLC purification for the measurement of prostanoids in urine. We have established the optimum precolumn and column conditions for this analysis. The manual extraction —HPLC procedure furnishes lower recoveries and higher coefficients of variation than those obtained by the automated on-line procedure. The automated system has been applied to prostanoid analysis of human urine samples from subjects exposed to lead.
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  • 92
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemically bonded phases (CBP) ; Physico-chemical characterization ; Silica-gel and porous glass ; Effects of structure and coverage density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two types of packing materials, porous glass (PG) and silica gel (SG) have been modified by mono- and difunctional octadecylchlorosilane. The packing surfaces before and after chemical modification have been characterized by CP/MAS NMR, SIMS, porosimetrical, elemental and chromatographic methods. On the basis of the physico-chemical and chromatographic data the PG and SG (of similar porosity) used as supports of chemically bonded phases for RP HPLC, have been compared.
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  • 93
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    Chromatographia 29 (1990), S. 254-258 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; On-line flame-AAS detection ; Hydraulic high pressure nebulization ; Trace metal speciation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Hydraulic high pressure nebulization is used as an effective way of on-line coupling of HPLC to flame-AAS for speciation of metal compounds in the ng range. Compared to coupling with a conventional nebulizer a signal enhancement by a factor of 7.5 (peak height) and 10.1 (peak area) for copper is obtained. Using an injected volume of 50 μL the detection limits for Cu, Fe, Ni and Cd are below 0.1 μg/mL (=5ng) and for Mg below 0.01 μg/mL (=0.5ng). The effects of HPLC flow-rate and nebulization nozzle diameter on the signal peak height have been investigated. The performance of the system is demonstrated using speciation of iron. A base-line separation of Fe(II) and Fe(III) is achieved within two minutes. Also species changes (Fe acetate to Fe citrate) can be analysed using the proposed system.
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  • 94
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    Chromatographia 37 (1993), S. 47-50 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; Phthalate esters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple method has been developed for the determination of dibutyl phthalate, di-(2-ethylhexyl) phthalate, diisodecyl phthalate, and di(2-ethylhexyl) adipate in industrial emissions. A cartridge packed with a modified silica gel is used as adsorbent and adsorbed compounds are eluted and analyzed by HPLC in normal and reversed phase system.
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  • 95
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Flavonoids ; Poplar tree taxonomy ; Fingerprinting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The RP-HPLC technique has been applied to the analysis of the flavonoid content of leaf extracts from various genotypes ofPopulus nigra andPopulus deltoides and from several of their hybrids. Two elution procedures different either as regards gradient program or the type of organic modifier used were checked to optimize the reliability of the results obtained. Before making any identification, the chromatographic profiles proved so typical of each species as to allow of their use as fingerprints in this type of taxonomic problem. Individual identifications were carried out by spiking real samples with known amounts of standard substances. The presence of flavonoid compounds previously identified was confirmed and a few new identifications were proposed.
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  • 96
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carboxylic acids ; Fruit juices ; Wine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A direct method for the simultaneous determination of tartaric, malic, lactic, acetic, citric, shikimic, fumaric and succinic acids in fruit juices and wines by isocratic reversed phase HPLC is reported. The variables (pH, ionic strength, flow and temperature) have been optimized by a modification of the original simplex method. The separation factor (s) and calibrated resolution product (r*) have been used as criteria for selectivity optimization. After validation, the method has been applied to the determination of carboxylic acids in apple, orange and lemon juices, white and red wines and musts during the fermenation process.
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  • 97
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    Chromatographia 29 (1990), S. 562-570 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin layer chromatography ; Azidothymidine ; Impurities of azidothymidine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary HPTLC densitometry and HPLC have been developed for the determination of potential impurities of azidothymidine (theymine, isothymidine, Az-Tr-thymidine, Ms-Tr-thymidine and Tr-alcohol). In HPTLC the substances were separated on silica gel with fluorescence indicator in 5∶95 methanol-chloroform for the simultaneous determination of Az-Tr-thymidine, Ms-Tr-thymidine and Tr-alcohol and in 10∶90 methanolchloroform for the simultaneous determination of thymine and isothymidine. Absorbance measurement (detection of reflectance) of separated substances was carried out “in situ” at 268 and 220 nm using four-level calibration (external standard) in the range of 25–100 ng thymine and isothymidine per spot. 50–200 ng Ms-Tr-thymidine and Az-Tr-thymidine per spot and 250–1000 ng Tr-alcohol per spot. For the HPLC determination of impurities two procedure are described one for thymine and isothymidine and the other for Ms-Tr-thymidine, Tr-alcohol and Az-Tr-thymidine. The first procedure was carried out using RP-18 stationary phase and methanol+aqueous 0.03 mol/l KH2PO4 (18+82, v/v) as the mobile phase. The temperature was 50°C and the detection wavelength 266 nm. In the second procedure the methanol content of the mobile phase was increased to 81% and the detection wavelength was changed to 210 nm. The detection limit of all impurities was 0.05 %. The concentration range for thymine was 1–40μg/ml and for the other impurities 1–20 μg/ml (for an injection volume of 10 μl). The results were evluated by linear regression analysis.
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  • 98
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    Chromatographia 29 (1990), S. 579-582 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Dynamic ion-exchange ; Rare earth elements ; Lactate complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Chromatographic behaviour of the rare earth elements on C-18 bonded silica reversed-phase material has been investigated in aqueous lactate media. The lactatocomplexes of the rare earths are distributed and fractionated on the bonded silica column by a mobile phase gradient technique in the presence of hydrophobic ions. The effects of the lactate concentration pH, methanol and hydrophobic ion concentrations in the eluents have been investigated in detail to have the best resulution of the adjacent rare earth elements. Port-column reaction with arsenazo(III) is used to detect the separated rare earth lactatocomplexes. This reversed-phase partition system is suited to separate and detect all rare earth elements within 40 min with good reproducibility.
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  • 99
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cyclodextrins inclusion complexes ; Structure-retention relationships ; Polycyclic aromatics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention behaviour of a group of polycyclic aromatic hydrocarbons having nearly equal ionization potentials but different molecular polarizability values was investigated using reversed-phase HPLC. Methanol-water binary systems containing β-cyclodextrin were applied as the mobile phase. The relationships between the capacity factors, molecular polarizabilities and the shape parameter of solute molecules are discussed.
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  • 100
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ginkgolides ; Ginkgo biloba L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The main terpenes ofGinkgo biloba L. extracts (bilobalide, ginkgolide A, ginkgolide B and ginkgolide C) have been separated by isocratic elution on a 3 μm C18 Spherical column using 2-propanol:water (10∶90) as eluent.
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