Quantitative measurement of N-acetyl-L-aspartic acid in urine by gas chromatography with negative-ion chemical ionization mass spectrometry.

A highly specific and sensitive assay for N-acetyl-L-aspartic acid has been developed. The trideuterated compound was synthesized and used as an internal standard for gas chromatography with negative-ion chemical ionization mass spectrometry. Urine samples were acidified and extracted with ethyl acetate, and the compounds converted into their pentafluorobenzyl ester derivatives. Under these conditions, sub-picogram amounts of the pure derivatives could be detected. Thus, only microliter volumes of urine samples have to be processed to achieve reliable quantification of "basal" levels of N-acetyl-L-aspartic acid.