Detection of mercaptopyridines and mercaptopyrimidines in planar chromatography with iodine–azide reaction as a detection system

Reaction between iodine and azide ion induced by mercaptopyridines and mercaptopyrimidines was utilized as a detection system in TLC and HPTLC. The developed plates were sprayed with a freshly prepared mixtures of sodium azide and starch solution adjusted to pH 5.5, and exposed to iodine vapour. The spots became visible as white spots on violet-grey background. The iodine–azide detection system has been proved to be the most favourable and enabled to detect quantities per spot in the range of 1–20 pmol (HPTLC) and 1–60 pmol (TLC). The iodine–azide tests were compared with other visualizing techniques commonly used in planar chromatography (iodine vapour and UV254). The developed method was applied to detection of thiopental in biological samples.