Biomedical subjects

J Wijsbeek

Publications and source records attributed to J Wijsbeek.

39 records · Page 3Linked to original sources

PubMedDate not supplied

Applicability of capillary gas chromatography to systematic toxicological analysis: occurrence of concentration-dependent retention behavior.

The retention behavior for a selection of acidic, neutral, and basic drugs was examined on four fused silica capillary columns in a splitless injection mode. Mixtures of n-alkanes and diisopropylamino-alkanes were also analyzed. The concentrations used ranged from 0.25-1000 ng/microL and injection volumes were either 2 or 4 microL. This corresponded to quantities of 1-4000 ng injected on the column. All substances showed concentration-dependent behavior: after being nearly constant or showing a decrease at low concentrations, retention times markedly increased when concentrations exceeded about 100 ng/microL (400 ng injected). At very high concentrations, peak splitting occurred. In the more pronounced cases, the differences caused by this concentration effect could reach values of over 100 retention-index units.

Chemical Phenomena↗

PubMedDate not supplied

Impact of biological matrix and isolation methods on detectability and interlaboratory variations of TLC Rf-values in systematic toxicological analysis.

The retention behavior of eight basic and neutral drugs, extracted from plasma, blood, and liver by five different methods (XAD-2, Extrelut, Elut-X, Elut-C18, chloroform) and developed in three chromatographic systems [MeOH, Me OH:BuOH:NaBr, CHCl3:MeOH (KOH)] was observed in parallel in two laboratories. The corrected Rf-values were compared with reference data from a data base with data for pure drugs. The biological matrix and/or the extraction severely lowered the precision and, to a lesser extent, the accuracy of the Rf-values as compared to pure drug data and to reference Rf-values. The intra- and interlaboratory variation was smallest in the MeOH system and largest in the CHCl3:MeOH (KOH) system. The observed irreproducibility is caused by the biological matrix (extraction has a large negative impact on the potentials of TLC in identification procedures). Precision and accuracy of extracted drugs were independent of the biological matrix and on the extraction method used.

Chemistry, Pharmaceutical↗

PubMedDate not supplied

Impact of biological matrix, drug concentration, and method of isolation on detectability and variability of retention index values in gas chromatography.

The retention indices of eight basic and neutral drugs extracted from plasma, blood, or liver homogenate by six different methods were calculated using temperature-programmed gas chromatography on OV-1 and SE-30 columns. Two concentrations were applied: 1 and 50 mg/L, respectively. The type of extraction had great influence on recovery and analytical background. The retention indices tended to be slightly concentration-dependent in that they were somewhat lower at higher drug concentration. Neither the biological sample nor the type of extraction exerted significant influence on scatter and mean value of the retention indices.

Chromatography, Gas↗