Surfactants modified silica phase for sorption studies of essential amino acids by thin layer chromatography

Abstract

A new thin layer chromatographic system comprising silica layer impregnated with an anionic surfactant, 0.001 M sodium dodecyl sulphate (SDS) as stationary phase and borate–phosphate buffer (pH 2.3) as mobile phase was identified as most favourable system for the mutual separation of l-histidine and dl-tryptophan. The presence of amines, inorganic anions and metal cations as impurities in the sample were examined for the separation of l-histidine from dl-tryptophan. The lowest detectable amount for these two amino acids, stability of the mixture of l-histidine and dl-tryptophan and reproducibility of the R F values were determined. Chromatographic parameters like separation factor and resolution for the separation of l-histidine and dl-tryptophan on silica TLC plates as well as on silica gel 60 F 254 HPTLC plates were evaluated and compared. Tryptophan as an impurity at 0.25 μg level in amino acids ( l-histidine, dl-methionine, l-lysine, dl-threonine and l-leucine) sample was detected as violet-blue fluorescing spot under UV radiation. The proposed method is rapid and applicable to the identification and separation of tryptophan in drug samples.