SIMPLE SPECTROFLUOROMETRIC DETERMINATION OF P-AMINOBENZOIC AND P-AMINOSALICYLIC ACIDS IN BIOLOGICAL-FLUIDS BY USE OF TERBIUM-SENSITIZED LUMINESCENCE

A novel, sensitive, and selective method has been developed for determ ination of p-aminobenzoic (PAPA) and p-aminosalicylic (PAS) acids in t he N-benzoyl-L-tyrosyl-PABA/PAS test. PAS is measured as a ternary com plex with terbium and EDTA (lambda(ex) = 324 nm, lambda(em) = 546 nm) in alkaline aqueous solution (pH similar to 12.6), whereas both compou nds (PABA and PAS) are measured as ternary complexes with terbium and tri-n-octylphosphine oxide (lambda(ex) = 292 nm, lambda(em) = 546 nm) in weakly acidic aqueous solution (pH similar to 5.5). We investigated and implemented optimum conditions for formation of these complexes, yielding respective detection limits for PAPA and PAS of 0.07 and 0.02 mu mol/L and ranges of application of 0-10 and 0-40 mu mol/L (final c oncentration). The method has been successfully applied to determinati ons of PAPA and PAS in urine and, after alkaline hydrolysis, to determ inations of PAPA in serum that has been deproteinized with acetonitril e. Within-run imprecision of the PAPA determination ranges from 0.8% t o 4.2% for urine samples and from 3.9% to 8.2% for serum samples; day- to-day imprecision varies from 3.2% to 10% for serum samples.