FULLY AUTOMATED HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC SEPARATION OF DL-AMINO ACIDS DERIVATIZED WITH ORTHO-PHTHALDIALDEHYDE TOGETHER WITH N-ISOBUTYRYL-CYSTEINE - APPLICATION TO FOOD SAMPLES

A method is presented that enables the fully automated precolumn derivatization of mixtures of DL-amino acids (DL-AA) with o-phthaldialdehyde together with N-isobutyryl-L(orD)-cysteine. isobutyryl-L(orD)-cysteine.HPLC on a 250 mm x 4 mm i.d. column packed with Shandon Hypersil ODS, 5-mu-m, and a linear gradient formed from 23 mM sodium acetate (pH 6.0) and methanol/acetonitrile (600 ml + 50 ml) separates completely an AA standard composed of 17 pairs of DL-AA (including Asn and Gln), Gly and the internal standard L-homo-Arg, within 75 min at a flow rate at 1 ml/min. Applications are shown of the determination of free D-AA isolated from an orange juice concentrate and from soy sauce, and the detection of D-AA in a gelatine total hydrolysate. In the case of these foodstuffs fluorescence detection (excitation at 230 nm, emission at 445 nm) allows the routine detection of 5-10 pmol per AA; and approx. 0.2-1 % D-AA, in an excess of L-AA, are quantifiable.