Application of iodine-azide reaction for detection of amino acids in thin-layer chromatography

The iodine-azide reaction was employed to TLC detection of sulphur-containing derivatives of protein and some non-protein amino acids. The derivatization reaction with phenyl isothiocyanate (PITC) took place directly on the plate before the developing step. Subsequently, the plates were sprayed with a mixture of sodium azide and starch solution in NP-TLC and in the case of RP-TLC sodium azide solution with starch incorporated into mobile phase and then exposed to iodine vapour. The spots became visible as white spots on violet–grey background. The obtained detection limits of PTC-derivatives have been compared with other visualizing techniques commonly used in TLC practice (UV254 and iodine vapour). The iodine-azide system has been proved to be the most favourable and enabled to detect quantities per spot in the range of 1–60 pmol (HPTLC) and 3–100 pmol (TLC).