K. Hrobonova

STUDY OF THE MECHANISM OF ENANTIOSEPARATION. I. CHIRAL ANALYSIS OF ALKYLAMINO DERIVATIVES OF ARYLOXYPROPANOLS BY HPLC USING MACROCYCLIC ANTIBIOTICS AS CHIRAL SELECTORS

The enantiomeric separation of alkylaminoderivatives of aryloxypropanols using macrocyclic bonded chiral stationary phases was studied. Teicoplanin and vancomycin chiral stationary phases were used to separate a large number of derivatives of aryloxypropanol enantiomers by HPLC in the polar-organic mode. By comparison of chromatographic parameters obtained by using both chiral stationary phases (CSPs), aspects of the enantioselective separation mechanism could be discerned. Originally, the polar organic mode was developed for chiral compounds that contained a minimum of two hydrogen bonding groups, resulting in a minimum of two hydrogen bonding interactions to the CSP. This work demonstrated that a combination of one hydrogen bonding interaction and one electrostatic interaction is equally effective. The environment (i.e., functional groups) nearest to the stereogenic center of the aryloxypropanols had the greatest effect on the enantioresolution. Teicoplanin CSPs produced the greatest ΔΔG°s and the best enantiomeric separations of these compounds. The site of a possible electrostatic interaction of these compounds is different from that found for amino acids.

MODIFICATION OF THE CHIRAL BONDING PROPERTIES OF TEICOPLANIN CHIRAL STATIONARY PHASE BY ORGANIC ADDITIVES. HPLC SEPARATION OF ENANTIOMERS OF ALKOXYSUBSTITUTED ESTERS OF PHENYLCARBAMIC ACID

The behaviour of teicoplanin-based chiral stationary phase (CHIROBIOTIC T) towards changes in organic and ionic modifiers in mobile phase was investigated in order to deduce suitable conditions for the liquid chromatographic enantioseparations of a series of alkoxysubstituted esters of phenylcarbamic acid. Methanol and acetonitrile were the non-ionic modifiers tested in the mobile phase, while different aliphatic carboxylic acids (formic acid, acetic acid, propionic acid, hexanoic acid) and bases (triethylamine, trimethylamine, diethylamine) were used as ionic modifiers. The influence of the nature and concentration of the modifiers on retention, selectivity, and resolution of enantiomers was investigated. Under these conditions, enantiomeric separations could be obtained for 3- and 4-alkoxysubstituted derivatives. The elution order of enantiomers was also determined.

HPLC Determination and MS Identification of Dehydroabietic Acid and Abietic Acid in Propolis

Abstract In the present study, the HPLC method on a C18 column with on‐line spectrophotometric and fluorimetric detection was used for separation and determination of dehydroabietic acid and abietic acid in propolis. The samples of propolis tincture were prepared prior to the HPLC analysis. The mobile phase for isocratic elution was methanol‐water 87:13 containing 0.05% formic acid. Abietic acid was detected with spectrophotometric detection at 238 nm, and dehydroabietic acid was detected with fluorimetric detection (excitation 225 nm, emission 285 nm). The limits of determination (signal/noise ratio 10) were 100 ng/mL for dehydroabietic acid and 200 ng/mL abietic acid. The calibration graphs were linear over a wide interval from the limit of determination to 1 mg/mL. Analytical recovery and reproducibility exceeded more than 89%. The developed method was used for analysis of propolis from Slovakia. Mass spectrometry was used for identification of the studied acids. The results demonstrated that dehydroabietic acid was present in all tested samples of propolis. Its content was different (3.7 µg/g–44.7 µg/g of propolis) depending on the source of propolis.

DETERMINATION OF NITROAROMATIC COMPOUNDS IN SOIL SAMPLES BY HPLC, USING ON-LINE PRECONCENTRATION

ABSTRACT The aim of this paper is to develop a simple HPLC method for trace analysis of 17 nitroaromatic compounds (nitrophenols, nitroanilines, nitrotoluenes, and others) in soil samples. To improve the limit of determination, on-line preconcentration of water extracts has been used. The separation was achieved by using the column packed with 10 µm LiChrosorb RP-18 and mixture methanol–water as mobile phase. The SPE cartridge (on-line coupled to an analytical column) containing a C-18 packing material was used to preconcentrate nitroaromatic compounds in water extracts of soil. The limits of the determination, at a wavelength of 254 nm (S/N = 5) 0.5–10 ppb, for studied analytes with recoveries of more than 85% were obtained. The developed method can be used for the study of nitroaromatic compounds during the degradation.

STUDY OF LOCAL ANAESTHETICS. CLVIII. CHROMATOGRAPHIC SEPARATION OF SOME DERIVATIVES OF SUBSTITUTED PHENYLCARBAMIC ACID ON A VANCOMYCIN-BASED STATIONARY PHASE

Vancomycin, immobilized on silica, served as the chiral stationary phase (CSP) in this investigation with a polar organic solvent as the mobile phase in high performance liquid chromatography (HPLC). Enantiomers of alkoxysubstituted esters of phenylcarbamic acid (local anaesthetic drugs) were examined in order to evaluate the enantiorecognition process. The chromatographic behavior was investigated in order to obtain a deeper insight into the enantiodiscrimination process. A variety of factors, including the nature and concentration of the ionic modifiers in the mobile phase were examined. Conditions for the enantioseparation of derivatives of phenylcarbamic acid were found. The interaction mechanism of the separations is discussed.

STUDY OF MECHANISM OF ENANTIOSEPARATION. II. HPLC CHIRAL ANALYSIS OF ALKOXYSUBSTITUTED ESTERS OF PHENYLCARBAMIC ACID

ABSTRACT The chromatographic separation of enantiomers of a series of 2-alkoxysubstituted esters of phenylcarbamic acid (C1−C10) were studied on (β- and γ-) cyclodextrin chiral stationary phases. The pH and concentration of organic modifier in the mobile phase were optimized. It was observed that the chromatographic performance of basic compounds could be strongly enhanced by increasing the pH of the mobile phase. Increasing the pH produced higher values for the enantiomeric resolution and the retention factors. This work demonstrated that the nonpolar interactions between the chiral stationary phase and the neutral molecules of these enantiomers had the greatest effect on enantioresolution.