Abstract
A method is presented that enables the fully automated precolumn derivatization of mixtures of DL-amino acids (DL-AA) witho-phthaldialdehyde together withN-isobutyryl-L(orD)-cysteine. HPLC on a 250 mm×4 mm i.d. column packed with Shandon Hypersil ODS, 5 μm, 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.
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