TLC of quaternary pyridinium aldoximes, antidotes of organophosphorus esterase inhibitors

Abstract

Quaternary pyridinium aldoximes have been analyzed by thin-layer chromatography. Their separation was adequate when silica plates were used with a mobile phase with a high water content. As a consequence of their limited migration, reversed-phase TLC was not appropriate for determination of the lipophilicity of quaternary pyridinium aldoximes. Displacement TLC of some quaternary pyridinium aldoximes is, nevertheless, possible using silica as stationary phase with water-acetone-hydrochloric acid mobile phases. Normal-phase TLC with different concentrations of organic modifier gave a series of RM values for the pyridinium aldoximes. Approximation of the different plots of RM against organic modifier concentration to straight lines afforded RM,0 values and the slopes of the lines. The RM,0 values and the slopes both serve as indicators of the hydrophilic character of the compounds.