Biomedical subjects

Dóra Visky

Publications and source records attributed to Dóra Visky.

6 recordsLinked to original sources

PubMed2006

Characterization of ester hydrolysis in terms of microscopic rate constants.

Hydroxide-catalyzed ester hydrolysis for molecules of coexisting species is quantitated in terms of microscopic rate constants, a new, species-specific physicochemical parameter. Relationships between the overall and component reactions, as well as the macroscopic and microscopic rate constants are deduced. Experimental techniques, evaluation methods, and feasibility are discussed. Species-specific, pH-independent rate constants of four coexisting, differently hydrolyzing microspecies are determined for the first time. Protonation of an alpha-amino and beta-imidazolyl site in amino acid esters has been found to accelerate the hydroxide-catalyzed hydrolysis by factors of 120 and 7.5, respectively, whereas they jointly exert a nearly 3000-fold acceleration. A total of 20 microscopic protonation equilibrium constants, as component parameters in the rate equations, have also been determined. The species-specific rate constants have been found to correlate with the site- and species-specific basicity of the leaving group and the NMR chemical shift of an adjacent proton. Individual contributions of the various microforms to the overall hydrolysis rate are depicted in microscopic reaction fraction diagrams.

Carboxylic Acids↗

PubMed2005

Facilitated column selection in pharmaceutical analyses using a simple column classification system.

In this paper, the performance of a previously developed classification system applied to pharmaceutical chromatographic analyses, is investigated. The separation of seven different drug substances from their respective impurities was studied. The chromatographic procedure for acetylsalicylic acid, clindamycin hydrochloride, buflomedil hydrochloride, chloramphenicol sodium succinate, nimesulide and phenoxymethylpenicillin was performed according to the corresponding European Pharmacopoeia (Ph. Eur.) monograph. The separation of dihydrostreptomycin sulphate was performed according to the literature. It is shown that the column ranking system is a helpful tool in the selection of a suitable column in these analyses.

Aspirin↗

PubMed2004

Characterisation of reversed-phase liquid-chromatographic columns by chromatographic tests comparing column classification based on chromatographic parameters and column performance for the separation of acetylsalicylic acid and related compounds.

Selection of RP-LC columns with suitable selectivity for a given analysis is difficult. For example, the European Pharmacopoeia (Ph. Eur.) and other official compendia for drug analysis only give a general description of the stationary phase in the operating procedure of a liquid chromatographic method. The need for a general test method to characterise RP-LC columns has been rising since the 1970s. A project to define a chromatographic procedure characterising RP-LC columns was started earlier. A procedure to measure test parameters was introduced and a classification of the columns, based on a minimal number of parameters, was obtained. This paper focuses on correlating the column classification with the selectivity obtained for a real separation. The separation of acetylsalicylic acid (aspirin) and related compounds was performed according to the Ph. Eur. monograph on the stationary phases previously characterised chromatographically. It was examined whether the classes of columns, determined using test parameter results, contain either suitable or unsuitable supports for the aspirin separation. The system suitability test prescribed by the Ph. Eur. in order to distinguish between suitable or unsuitable columns for this separation was also evaluated.

Aspirin↗

PubMed2003

Characterisation of reversed-phase liquid chromatographic columns by chromatographic tests. Rational column classification by a minimal number of column test parameters.

The European Pharmacopoeia (Ph. Eur.) and other official compendia give only a general description of the stationary phase in the description of a liquid chromatographic method. Therefore the selection of a column giving suitable selectivity presents difficulties. Earlier, a test procedure was proposed that allows to measure 36 chromatographic parameters which have been described for characterising stationary phases. This procedure was carried out on 69 reversed-phase liquid chromatography (RP-LC) columns. This paper focuses on the classification of RP-LC stationary phases based on chromatographic parameters. A chemometric study was conducted using 24 parameters that could be measured in a repeatable and reproducible way. Principal component analysis was used to classify the columns and to estimate the minimal number of parameters necessary for a rational classification. It is shown that after reducing the number of parameters from 24 to four or three, similar classifications were obtained. The column classifications were compared to the European Pharmacopoeia stationary phase description and to the column properties obtained from the manufacturers.

Chromatography, Liquid↗

PubMed2002

Characterisation of reversed-phase liquid chromatographic columns by chromatographic tests. Evaluation of 36 test parameters: repeatability, reproducibility and correlation.

The European Pharmacopoeia (Ph. Eur.) or other official compendia give only a general description of the stationary phase in the description of a liquid chromatographic method. Therefore the selection of a column giving suitable selectivity presents difficulties. Earlier, a test procedure was proposed that allows measurement of a number of parameters which are reported to be representative for stationary phase characteristics. This paper describes how the test procedure was applied on 69 RP-LC C18 columns. Chromatographic parameters obtained as test results were evaluated, and their repeatability, reproducibility and correlation were examined.

Chromatography, High Pressure Liquid↗

PubMed2002

Minimal number of chromatographic test parameters for the characterisation of reversed-phase liquid chromatographic stationary phases.

This paper focuses on the classification or differentiation of RP-HPLC columns based on measured chromatographic properties. A chemometric study has been conducted on a published data set consisting of 85 RP-HPLC columns and on a data set consisting of 47 self-tested columns. Principal component analysis enables determination of the number of parameters necessary for a rational differentiation. The results show that reducing the number of parameters for such differentiation still allows classification of the columns just as a higher number did. It is shown that three test parameters produce a classification similar to that obtained with five parameters.

Chromatography, High Pressure Liquid↗