Determination of naproxen with flow injection chemiluminescence of Ru(bpy)32+-PbO2 system and its application for the binding study of naproxen to protein

A flow injection method based on Ru(bpy)32+-PbO2 chemiluminescence system was developed for the determination of naproxen. The factors affecting the CL intensity were performed including the amount of PbO2 and H2SO4, pH of buffer and concentration of Ru(bpy)32+. Under the optimum conditions, naproxen has a linear calibration graph in the range of 2 × 10−8-6 × 10−6 mol/L with a limit of detection (S/N = 3) of l.0 × 10−8 mol/L, The correlation coefficient was 0.9976 (n = 12) with a relative standard deviation of 3.4% for 15 determinations of l × 10−6 mol/L of naproxen. Combining with ultrafiltration, this method was successfully applied to study naproxen-protein interaction. The binding constants (K) to bovine serum albumen (BSA) were K1 = 2.06 × 106L/mol and K2 = 2.18 × 107 L/mol, and to human serum albumen (HSA) were K1 = 4.80 × 106 L/mol and K2 = l.25 × 107 L/mol, respectively. The correlation coefficients given by Scatchard plot and Klotz plot were satisfied, indicating that studied drug has two types of binding site in the molar ratio range studied. The number of the binding site (n) on one molecule of BSA were n1 = 6.79 and n2 = 1.88, and of HSA were n1 = 1.22 and n2 = 1.80, respectively. The proposed method provided a sensitive, reliable and simple technique for studying naproxen-protein interaction and was for the first time applied to the determination of the unbound fraction of naproxen in its human serum albumin equilibrated solution.