KINETIC DETERMINATION OF SALICYLIC-ACID, DIFLUNISAL AND THEIR MIXTUREBASED ON LANTHANIDE-SENSITIZED LUMINESCENCE

The combined use of kinetic and equilibrium measurements, obtained wit h the aid of the stopped-flow mixing technique, allowed the developmen t of a simple, fast direct method for the simultaneous determination o f salicylic acid and diflunisal in untreated serum samples that can be readily applied to routine analyses. The method is based on the forma tion of ion-association complexes between the cationic surfactant cety ltrimethylammonium bromide and the ternary anionic chelates formed by salicylate and diflunisal with terbium(III) and EDTA in a basic medium . The intramolecular energy transfer from salicylate or diflunisal to terbium(III) gives rise to luminescence emission by the lanthanide ion . The calibration graphs thus obtained are linear over a wide concentr ation range and the detection limits are in the nanogram per millilitr e region. Within-assay and between-assay relative standard deviation r anged from 2.6% to 3.6% and from 1.3% to 8.5%, respectively. Mixtures of salicylic acid and diflunisal in ratios between 6:1 and 1:12 can be satisfactorily resolved. The proposed method was applied to the direc t determination of these compounds in serum with recoveries of 92.7-10 9.0% for salicylic acid and 86.4-110.9% for diflunisal.