Separation of Amino Acids as Phenyl Thiocarbamyl Derivatives by Normal and Reversed-Phase Thin-Layer Chromatography

To separate groups of amino acids we have used a process of deriva-tization involving formation of phenyl thiocarbamyl derivatives. Phenyl isothiocyanate was used as derivatization reagent. This particular reagent was chosen because the proposed method of detection entailed use of the iodine-azide reaction, which can be applied to sulfur compounds because their properties induce this reaction. Because amino acids do not belong to this group, it was necessary to perform a suitable transformation. The derivatization process was performed directly on the plate or in a tube, depending on the stationary phase chosen. After normal-phase (NP) TLC development with appropriate mobile phases, the plate was sprayed with a freshly prepared mixture of sodium azide and starch solution and exposed to iodine vapor. In reversed-phase TLC the plates were developed with mobile phase containing sodium azide and starch solution and then exposed to iodine vapor without being dried. In both NP and RP-TLC the catalytic effect of the C=S bond promoted the derivatization reaction and the compounds became visible as white spots on a violet-gray background. Our objective was to resolve groups of amino acids. After several experiments in pursuit of suitable mobile phases we accomplished separations by 2D NP-TLC and 1D RP-TLC.