The simultaneous detection and quantification of p-aminobenzoic acid and its phase 2 biotransformation metabolites in human urine using LC-MS/MS.

BACKGROUND: p-Aminobenzoic acid (PABA) can be used as a probe substance to investigate glycine conjugation, a reaction of phase 2 biotransformation. METHODOLOGY/RESULTS: An LC-MS/MS method for simultaneous quantification of PABA and its metabolites from human urine was developed and validated. The metabolites can be quantified with acceptable precision and accuracy directly from human urine samples after ingestion of 550 mg PABA. CONCLUSION: The developed LC-MS/MS assay is to our knowledge the first method available for the simultaneous quantification of PABA and its glycine conjugation metabolites in human urine and provides important quantitative data for studies of this phase 2 biotransformation pathway.