Liquid-chromatographic measurement of p-aminobenzoic acid and its metabolites in serum.

This is a high-performance liquid-chromatographic method for measuring p-aminobenzoic acid (PABA) and its metabolites in plasma or serum. Samples are deproteinized, then extracted with organic solvents before chromatography. For quantification, the peak height of the individual compound is compared with that of the internal standard. Analytical recoveries ranged from 41% to 100%, depending on the compound studied. Comparison of patients' samples after oral administration of either N-benzoyl-L-tyrosyl-p-aminobenzoic acid or free PABA revealed that PABA is extensively metabolized and conjugated to either p-acetamidobenzoic acid, p-aminohippuric acid, or p-acetamidohippuric acid. PABA concentrations in serum as measured with the Bratton-Marshall ultraviolet spectrophotometric procedure would appear predominantly to reflect measurements of metabolites, with only a minor contribution from PABA itself.