Quantitation of the antitumor agent N-(phosphonacetyl)-L-aspartic acid in human plasma and urine by gas chromatography-mass spectrometry-selected ion monitoring.

N-(Phosphonacetyl)-L-aspartic acid (PALA) is an antitumor agent which is currently under clinical study. A gas chromatography--mass spectrometry--selected ion monitoring assay procedure using [13C]PALA as the internal standard has been developed for the quantitation of PALA in biological samples. Standard curves which related ion intensity peak height ratios (m/e 220/221) to PALA concentrations in plasma and urine were described by a non-linear least square analysis with correlation coefficients of R2 greater than 0.995 and greater than 0.996, respectively. Over concentration ranges for PALA of 1--60 micrograms/ml of plasma and 1--160 micrograms/ml of urine the coefficient of variation from the fitted curve was 4--18%. This methodology has been used to quantitate PALA in human plasma samples in a study on the clinical pharmacology of the drug.