Simple and rapid determination of the active metabolite of nabumetone in biological fluids by heavy atom-induced room temperature phosphorescence

Abstract

A simple, selective and sensitive heavy atom induced-room temperature phosphorimetric method is described for the determination of 6-methoxynaphthylacetic acid, main metabolite of nabumetone, in biological fluid. The phosphorescence signals are a consequence of intermolecular protection when analytes are, exclusively, in presence of heavy atom salt and sodium sulfite as an scavenger to minimize room temperature phosphorescence quenching. This technique enables us to determine analytes in complex matrices without the need for a tedious prior separation process. Optimized conditions for the determination were 0.12 M TlNO 3. An amount of 0.025 M sodium sulfite and pH 7.5 (adjusted with 0.1 M sodium hydrogen phosphate-dihydrogen phosphate buffer solution). The delay time, gate time and time between flashes were 180, 1500 μs, and 5 ms, respectively. The maximum phosphorescence signal appeared instantly and the intensity was measured at λ ex = 328.4 nm and λ em = 544.4 nm. The response obtained was linearly dependent on concentration in the range of 20–1000 ng mL −1. The detection limit, according to error propagation theory, was 11.6 ng mL −1 and the detection limit as proposed by Clayton, was 17.4 ng mL −1. The repeatability was studied by using 10 solutions of 100 and 800 ng mL −1 of metabolite; if the theory of error propagation is assumed the relative error is 4.3 and 0.66%. The S.D. of replicates was found to be 2.2 and 11.0 ng mL −1. This method was successfully applied to the analysis of 6-methoxynaphthylacetic acid in human serum and urine.