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.