Determination of D- and L-aspartate in amino acid mixtures by high-performance liquid chromatography after derivatization with a chiral adduct of o-phthaldialdehyde.

A sensitive and convenient method for the simultaneous determination of D- and L-aspartic acid in amino acid mixtures is described. The method involves derivatization of the mixture with a chiral fluorogen, followed by high-performance liquid chromatography on a reverse-phase column. The fluorogen used is an adduct of o-phthaldialdehyde with an optically active thiol, N-acetyl-L-cysteine. The sensitivity and accuracy of this method is similar to that using adducts of o-phthaldialdehyde with the achiral thiol, 2-mercaptoethanol. Five picomoles of D-aspartate can be accurately detected in the presence of a 100-fold excess of L-aspartate with a total analysis time (including derivatization) of 10 min.