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-cysteine 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. Maximum resolution and adequate retentions were achieved with a 0.05 M sodium dodecyl sulphate/3% propanol mobile phase at pH 3. The reproducibility was lower than 1.0% at a 1x10(-4) M concentration level and between 0.6 and 2.2% for 1x10(-6) M. The determination of glycine, lysine, methionine and threonine in pharmaceutical formulations gave recoveries, with respect to the values declared by the manufacturers, in the 90-105% range.