DETERMINATION OF AMINO-ACIDS IN HUMAN PLASMA BY LIQUID-CHROMATOGRAPHYWITH POSTCOLUMN NINHYDRIN DERIVATIZATION USING A HYDROXYAPATITE CARTRIDGE FOR PRECOLUMN DEPROTEINATION

Amino acids in human plasma were determined by liquid chromatography w ith postcolumn ninhydrin derivatization using a hydroxyapatite cartrid ge for precolumn deproteination. S-Carboxymethyl-L-cysteine, D-phenylg lycine and S-aminoethyl-L-cysteine were found to be suitable internal standards. The proposed method is simple, rapid (deproteination time l ess than 1 min) and reproducible [relative standard deviation below 3% except for low-level aspartic acid (n = 3)]. The average recovery of 25 amino acids was above 90%. The elution time of amino acids in human plasma was approximately 2 h. Protein binding of tryptophan was also determined by the proposed method. The analytical data for amino acids in human plasma deproteinated using the proposed and published method s (5-sulphosalicylic acid and ethanol) were compared.