Quantification of D-amino acids in human urine using GC-MS and HPLC

The relative amounts of free D-amino acids (D-AA) in the urine of seven healthy volunteers (age 27 to 49 years) were determined using chiral phase (Chirasil-L-Val) capillary gas chromatography in conjunction with selected ion monitoring mass spectrometry. The absolute amounts of free D-AA were determined by pre-column derivatization of the amino acids witho-phthaldialdehyde andN-isobutyryl-L-cysteine followed by high-performance liquid chromatographic separation and fluorescence detection of the isoindol derivatives formed. The following most abundant D-AA were found (highest and lowest absolute and relative amounts): D-Ser (379.8 - 30.1µMol/L; 56.5 - 19.0%), D-Ala (53.8 - 7.6µMol/L; 19.6 - 5.7%), D-Thr (5.8 - 0.25µMol/L; 3.4 - 1.0%), D-Val (3.7 - 0µMol/L; 4.2 - 0%), and D-Phe (3.5 - 0.35µMol/L; 4.8 - 1.4%).