DETERMINATION OF AMINO-ACIDS BY MICELLAR HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND PRE-COLUMN DERIVATIZATION WITH O-PHTHALALDEHYDE AND N-ACETYL-L-CYSTEINE

Micellar liquid chromatography of proteic primary amino acids with pre -column derivatization with o-phthalaldehyde (OPA) and N-acetyl-L-cyst eine was studied, using mobile phases containing a short-chain alcohol . The modification of pH gave a large variation of the retention as a result of the protonation of the carboxylate group of amino acids. Max imum resolution and adequate retentions were achieved with a 0.05 M so dium dodecyl sulphate/3% propanol mobile phase at pH 3. The reproducib ility was lower than 1.0% at a 1x10(-4) M concentration level and betw een 0.6 and 2.2% for 1x10(-6) M. The determination of glycine, lysine, methionine and threonine in pharmaceutical formulations gave recoveri es, with respect to the values declared by the manufacturers, in the 9 0-105% range.