Spectrofluorimetric determination of urinary p-aminobenzoic and p-aminosalicylic acids in the BT-PABA/PAS test of pancreatic function

Abstract

Spectrofluorimetry was investigated as an alternative to HPLC for determining p-aminobenzoic acid and p-aminosalicylic acid in the N-benzoyl- L-tyrosyl- p-aminobenzoic acid/ p-aminosalicylic acid test of pancreatic exocrine function. Urine specimens were hydrolysed for 30 min in 4 M NaOH at 100 ° C. The fluorescence of p-aminobenzoic acid was measured in dimethyl sulphoxide solution ( λ ex = 300 nm, λ em = 340 nm) and that of p-aminosalicylic acid in sodium acetate buffer, pH 4.0 ( λ ex = 297 nm, λ em = 394 nm). The linear range was 0.038−8 mM for p-aminobenzoic acid and 0.051−12 mM for p-aminosalicylic acid, withinbatch precision was 2.2% and 5.5%, respectively, and the entire analysis could be completed within 40 min. Although not eliminated, drug interference was greatly reduced in comparison with colorimetry. In 23 consecutive pancreatic function tests there was an excellent correlation between the p-aminobenzoic acid/ p-aminosalicylic acid excretion index obtained by fluorimetry and the results from HPLC analysis ( y = 0.914 x + 0.070, r = 0.987, p < 0.001). The method is simple, cost-effective and may be particularly valuable in developing countries having a high incidence of chronic pancreatitis.