摘要:

The mechanism of chiral selectivity of a difunctional polymer imprinted with dansyl-L-phenylalanine was investigated using the polymer as an HPLC stationary phase. Temperature studies revealed that the mass transfer of the imprinted enantiomer with the polymer was sluggish at low temperatures, leading to a non-equilibrium migration down the column. Conversely, retention of the non-imprinted enantiomer was controlled by a thermodynamic equilibrium over the entire temperature range of the study. Variation of the structure of the analyte indicated a single leading interaction between both enantiomers of dansyl-phenylalanine and the polymer phase; a hydrogen bonding interaction between the carboxylic acid group of dansyl-phenylalanine and pyridinyl sites on the polymer.

ISSN:1082-6076    

DOI:10.1081/JLC-100101653

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Poly(methyl methacrylate) grafted with poly(dimethyl-siloxane) was investigated by size exclusion chromatography coupled with refractometric and low-angle laser light scattering detectors. Using successively toluene and tetrahydrofuran as eluents, a variation in chemical composition and molecular weight of individual copolymer blocks as a function of hydrodynamic volume were measured. Chemical composition distribution and heterogeneity parameters of the copolymerization product were approximated and compared with the results obtained by supercritical fluid extraction fractionation and by fractionation in demixing solvents.

ISSN:1082-6076    

DOI:10.1081/JLC-100101654

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A new HPLC-DAD method for separation and identification of the main phenolics present inin vivoandin vitrobiomass ofHypericum perforatumandHypericumandrosaemumhas been developed. This method accomplished the direct identification of 22 compounds including flavonoids, hypericins, phloroglucinols, and phenolic acids. The HPLC profiles obtained in the course of this work clearly evidenced a distinct phenolic production betweenin vivoandin vitrobiomass. For examplecalliand suspended cells produced mainly xanthones while inin vivoplants of both species these compounds were not detected.

ISSN:1082-6076    

DOI:10.1081/JLC-100101655

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The lipophilic character of a series of new isoxazolyl-naphthoquinones has been studied. Partition chromatography procedures (RP-HPLC and RP-TLC) were developed for determining the log Po-w(n-octanol/water partition coefficient) values. The experimental values from these methods were validated by comparison with those obtained from the conventional shake flask method, except with the more lipophilic because they have poor water solubility. Also, the log Po-wwas calculated using a CLOGP computer programme.

ISSN:1082-6076    

DOI:10.1081/JLC-100101656

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This study investigated various acetals for the purpose of improving the supercritical fluid extraction (SFE) using carbon dioxide of β-carotene from an aqueous matrix. Results showed that the presence of water decreases the extraction efficiency of β-carotene from paprika by a factor of 2. Upon the addition of 2,2-dimethoxypropane (DMP), the extraction efficiency of β-carotene from wet paprika was increased by a factor of about 2.5 and from dry paprika a factor of 1.5. Diethoxypropane (DEP) and triethylorthoformate (TEOF) proved to be less effective for improving the extraction of β-carotene from paprika. Although the addition of an acid catalyst enhances the reaction between DMP or TEOF with water under SFE conditions, an actual decrease in the extraction of carotene from paprika was found. It is possible, even without an acid catalyst, that DMP can remove a little water, improving extraction efficiency. However, its main impact on improving SFE seems to be as a modifier.

ISSN:1082-6076    

DOI:10.1081/JLC-100101657

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We have used a squalane adsorbed C18phase as presumably a bulk-like stationary phase to secure a simple partition mechanism for solute retention in reversed phase liquid chromatography, and have evaluated the nondispersive (specific) functional group-solvent interaction separately by measuring the retention data of carefully selected solutes in 60/40, 70/30, and 80/20 (v/v%) methanol/water eluents at 25,30,35,40,45, and 50°C. We have found that the absolute magnitude of the carbonyl group (in acetophenone)-mobile phase specific interaction enthalpy is much greater than that of the hydroxyl group (in phenol)-mobile phase specific interaction enthalpy. If we consider the overall differential solute transfer free energy for a pair of polar and nonpolar solutes of the same size, the entropic contribution is dominant for the BT/phenol pair, and the enthalpic contribution, for the ethylbenzene/acetophenone pair. On the other hand, for a pair of nonpolar solutes, the entropic contribution to the differential free energy of solute transfer is much lower than the enthalpic contribution, and the variation in the differential entropy of solute transfer with respect to mobile phase composition is much smaller than the variation in the differential enthalpy, too.

ISSN:1082-6076    

DOI:10.1081/JLC-100101658

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A Liquid Chromatography (LC) method using volatile ion pairing agents and Evaporative Light Scattering Detector (ELSD) was developed. The separation of a series of three common inorganic anions (Cl−, NO3−and SO42−) and three organo–phosphonic anions (Methyl, ethyl and propylphosphonic acids) was achieved on a reversed–phase C18column with pentylammonium or heptylammonium formiate as ion pairing agent.

ISSN:1082-6076    

DOI:10.1081/JLC-100101659

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

To meet the requirement of quantitative analysis, this work re-investigated the parameters relevant to the separation of seven fluoroquinolone antibacterials, ciprofloxacin, enoxacin, lomefloxacin, norfloxacin, ofloxacin, pefloxacin, and sparfloxacin, based on the method developed previously in our laboratory. With the optimum conditions obtained: electro- phoretic media - 65 mM sodium borate, 35 mM sodium dihydrogen phosphate, 60 mM sodium cholate, pH 7.3 / acetonitrile (72 : 28, v/v); fused silica capillary - 50 μm I.D., total length 67 cm, detection length 52 cm; hydrodynamic injection - 60 mbar, 3 sec; voltage - 27 kV; temperature - 25°C and detection wavelength - 275 nm, the fluoroquinolones were well separated within 8.5 min. After being validated the method was used for the assay of the formulation products. The assay results were within 95∼105 % of their label claims. The method should be applicable to the analysis of these and other similar formulation products containing these drugs.

ISSN:1082-6076    

DOI:10.1081/JLC-100101660

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A High Performance Liquid Chromatography (HPLC) method utilizing nonporous silica particle technology has been developed for the assay of an analgesic mixture containing aspirin, caffeine, and codeine. The separation and quantitation of the mixture was achieved on a column packed with nonporous silica particles chemically bonded with octadecylsilane (3.0 μm particles) using a mobile phase of 95:5 v/v 0.01 M phosphate buffer (pH 3.0)-methanol at a flow rate of 600 μL/min with UV detection at 216 nm. The separation was achieved within 3 min. The method showed linearity for aspirin in the range 40–242.5 μg/mL, and for caffeine and codeine in the range 7.5–45 μg/mL. Inter- and intra day precision ranged from 0.12–1.95% for aspirin, 0.07–.69% for caffeine, and 0.06–1.69% for codeine. The limits of detection for the analytes were 157 ng/mL for aspirin, 28 ng/mL for caffeine, and 30 ng/mL for codeine based on a signal-to-noise ratio (S/N) of 3 and a 10 μL injection.

ISSN:1082-6076    

DOI:10.1081/JLC-100101661

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Capillary gel electrophoresis is a powerful method for separation of DNA fragments. Usually, water based poly-(acrylamide) gels are employed. In order to release compressions due to intra-molecular base pairing within DNA fragments, it is often necessary to incorporate denaturing agents (e.g. urea, formamide) and/or to operate at elevated temperatures. In this work we have studied the performance of gels in non-aqueous solvents. Poly(dimethylacrylamide) gels in both formamide and N-methyl formamide were prepared. The formamide based gels showed a poor stability under normal capillary electrophoresis conditions,1 rapidly developing voids at moderate electric field strengths. However, N-methyl formamide based gels were more stable and could be employed for electrophoretic separations of oligonucleotides. Sieving properties similar to those of regular water-based poly(acrylamide) gels, were observed. Non-aqueous gels without any additives had a considerable denaturing power, in fact, comparable to water-based gels containing 7 M urea. Interesting influences on the separation selectivity when utilizing different concentrations of N-methyl formamide were observed, which are discussed in the paper.

ISSN:1082-6076    

DOI:10.1081/JLC-100101662

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor