摘要:

The chiral separation of fourteen Substance P antagonists, substituted at a benzylic carbon to generate a chiral centre, was investigated using Chiracel OD-H and Chiralpak AD stationary phases. The nature of an N-substituent, distant from the chiral centre, was found to modulate separation selectivity. Aromatic substitution on the benzyl group also affected separation selectivity, but to a lesser degree. Some complementary character between Chiracel OD-H and Chiralpak AD was seen, but selection of the optimal phase did not appear predictable. The effect of temperature was also unanticipated, with some compounds showing the expected decrease of separation selectivity with temperature, whereas, an example of an improvement in separation selectivity with temperature to give an entropically controlled separation was also observed. This serves to highlight the complex nature of enantioselective interactions using chiral polymers and suggests that, given an unknown compound in this series, adequate separation conditions are difficult to predict.

ISSN:1082-6076    

DOI:10.1081/JLC-100100508

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Separations of small peptides (di-, tri- and tetrapeptides)using ion-pair chromatography and evaporative light scattering detection havebeen investigated with a porous graphitic carbon stationary phase, Hypercarb®.Five perfluorinated carboxylic acids (trifluoroacetic (TFA), pentafluoropropanoic(PFPA), heptafluorobutanoic (HFBA), nonafluoropentanoic (NFPA) and tridecafluoroheptanoic(TDFHA) acids) have been evaluated as ion-pairing agents. Influence of thepercentage of organic modifier, concentration, and chain length of the ion-pairingagent on the retention factors, k, has been examined. Equilibration timeswere also studied. Separations of dipeptides or tri- and tetrapeptides arepresented using HFBA and NFPA at 20 mM and TDFHA at 2.5 mM.

ISSN:1082-6076    

DOI:10.1081/JLC-100100499

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Two RP-HPLC methods are described for the determination of the compounds in 2,2-dimethyl-3-propionaldehyde synthesis mixtures. All the other compounds, except aliphatic aldehydes, are determined by a gradient programmed method using UV/DAD and RI detectors in series. Aldehydes are determined as their 2,4-dinitrophenylhydrazone derivatives using a UV/DAD detector. The selection between different columns and detectors is made with a column switching technique. The eluents and column temperature are selected so, that only one HPLC instrument is needed.

ISSN:1082-6076    

DOI:10.1081/JLC-100100500

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Synthetically and pharmaceutically interesting racemic amino alcohols with two adjacent chiral centres were analysed by means of indirect high performance liquid chromatography. For resolution of the enantiomers, the recently developed chiral derivatizing agent (1R,2R)-1,3-diacetoxy-1-(4-nitrophenyl)-2-propyl isothiocyanate ((R,R)-DANI) was applied. The diastereomeric thioureas produced after derivatization were separated under reversed-phase conditions. Of the organic modifiers applied in the eluent, methanol proved much more effective than acetonitrile.

ISSN:1082-6076    

DOI:10.1081/JLC-100100501

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The separation of side chain dihydroxylated vitamin D3metabolites by inclusion high performance liquid chromatography using cyclodextrin (CD) as the mobile phase additive was examined. 24,25-Dihydroxyvitamin D3and its 3-epimer were clearly separated by the addition of γ-CD to the mobile phase using acetonitrile as the organic modifier. The separation of the 25-epimers of 25,26-dihydroxyvitamin D3has been done, to a certain extent, with the mobile phase using methanol and dimethylated β-CD as the organic modifier and the additive, respectively. These separation methods were applied to the detection of the metabolites in the plasma of the rat administered 25-hydroxyvitamin D3. These metabolites were also identified by liquid chromatography/tandem mass spectrometry after derivatization.

ISSN:1082-6076    

DOI:10.1081/JLC-100100502

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Description of chromatographic retention mechanism in the systems with ternary mobile phase is very complex. Designation of the effect of individual mobile phase components on this process is difficult. The number of moles (or molecules) of less polar solvents of mobile phase referring to one mole (or molecule) of polar solvent must be taken into account. In this connection, a new method of experimental data presentation was proposed. The association effects and changes of surface phase composition were analysed. Experimental data are presented as relationships RMvs. (x1/x2)3and RMvs. (x1/x3)3. The influence of a chromatographed substance on the retention process was also analysed. The relationships mentioned above enable the effect of individual solvent on the chromatographic process.

ISSN:1082-6076    

DOI:10.1081/JLC-100100503

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A large-scale separation of taxol from semi-purified bark extract ofTaxus yunnanesiswas investigated. The chromatographic behavior of taxol and two close eluting analogues, cephalomannine and 7-epi-10-deacetyltaxol, was systematically studied on a C18bonded phase column with different mobile phases in reverse phase mode. According to the notably different selectivity of the methanol and acetonitrile with water in the mobile phase and the most important requirement of capacity in preparative chromatography, the optimum suitable mobile phase used in a large-scale isolation of taxol and 7-epi-10-deacetyltaxol on a preparative C18column was given. Cephalomannine was eliminated by ozonolysis and, then after, separated throughout a normal phase silica column. The whole large-scale process for high purity taxol from the bark extract fromTaxus yunnanesisconsisted of a preliminary purification with Biotage FLASH 150i system based on a prepacked normal phase silica cartridge, followed by using a C18Nova-pak™ column in a Waters PrepLC™ 4000 preparative HPLC system.

ISSN:1082-6076    

DOI:10.1081/JLC-100100504

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An analytical method of triflusal in human plasma was developed using semi-microbore HPLC equipped with automated column switching system.p-Toluic acid which is the structural analogue of triflusal, was used as an internal standard and 2 M HCl was employed as a stabilizer. The load phase and mobile phase were prepared using acetonitrile and 20 mM KH2PO4with the volume ratios of 10:90 (pH 2.5) and 43:57 (pH 2.3), respectively. The signals were monitored by a UV detector at 275 nm with flow-rate of load phase, 500 μL/min, and mobile phase, 100 μL/min, respectively. The retention time of triflusal andp-toluic acid was about 20.2 min and 16.4 min, respectively. The detection limit of triflusal in human plasma was 0.01 μg/mL and the limit of quantitative analysis was 0.05 μg/mL. The accuracy of the assay was from 97.76% to 116.51% while the intra-day and inter-day coefficient of variation of the same concentration range was less than 15%. This analytical method demonstrated excellent sensitivity, reproducibility, specificity, and speed using the plasma sample. This method could be successfully applied to evaluate the bioavailability of triflusal in human subjects without time-consuming sample clean-up after oral administration of low dose.

ISSN:1082-6076    

DOI:10.1081/JLC-100100505

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The conditions were selected for the reversed phase HPLC separation (phosphate buffer pH = 7.4 / methanol) ofN-oxyethylates ofN-methylaniline andN-ethylaniline on C18 columns, depending on the oxyethylene chain length. The use of the “mixed-mode” C18/anion column provided the possibility for simultaneous separation of oxyethylates, as well as,N,N-dimethylaniline andN,N-diethylaniline. UV spectra were taken for the compounds studied in order to find the optimum wavelengths for the detection procedure.

ISSN:1082-6076    

DOI:10.1081/JLC-100100506

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In high-performance liquid chromatography, the reversed-phase mode column is used most popularly. In the reversed-phase mode separation, several interactions between the stationary phase and analytes are concerned, i.e., partitioning, adsorption, hydrogen bonding, and π-π interactions. In this paper, a π-π interaction effect on high performance liquid chromatographic separation was studied using someN-substituted aminopropyl modified silyl silica gel stationary phases bearing aromatic moieties in their structures. A series of aromatic polycyclic hydrocarbons, i.e., benzene, naphthalene, phenanthrene, and naphthacene, were retained and separated on those columns in the order of their aromaticities, while no retention was observed by the non-substituted aminopropyl modified silyl silica gel column. These results strongly supported the existence of π-π interactions betweenN-substituted aminopropyl modified silyl silica gel and the hydrocarbons.

ISSN:1082-6076    

DOI:10.1081/JLC-100100507

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor