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

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 RF 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 F254 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.