Urinary p-aminobenzoic acid determined in the pancreatic function test by liquid chromatography, with electrochemical detection.

We describe a liquid-chromatographic procedure for determining urinary p-aminobenzoic acid (PABA) in the exocrine pancreatic function test. The urine specimen, collected for 6 h after oral administration of N-benzoyl-L-tyrosyl-p-aminobenzoic acid, is hydrolyzed in 4 mol/L NaOH containing m-hydroxybenzoic acid as internal standard, to free PABA metabolites, then diluted and injected into the chromatograph. PABA and the internal standard are eluted from a reversed-phase C18 column with phosphate buffer (0.2 mol/L, pH 3.5)/acetonitrile, 87.5/12.5 (by vol), and detected with an electrochemical detector at +1100 mV. Urinary PABA concentration as measured by this method agreed well with that by colorimetry involving p-dimethylaminocinnamaldehyde. The present procedure is specific for PABA, precise, and fairly rapid. We hope that the present method will minimize instances of interference from drugs, which cannot be avoided in the colorimetric method.