Rapid simultaneous determination of four non-steroidal anti-inflammatory drugs by means of derivative nonlinear variable-angle synchronous fluorescence spectrometry.

A rapid, simple, and inexpensive spectrofluorimetric method has been proposed for the simultaneous quantification of diflunisal, salicylic acid, fenoprofen, and 6-methoxy-2-naphthylacetic acid (6MNA). First-derivative nonlinear variable-angle synchronous fluorescence spectrometry has been developed to improve the selectivity of fluorescence measurements without loss of sensitivity. It allows the simultaneous determination of different substances in a mixture from a single spectrum based on a single scan. The analyses were performed in an ethanol-water (70%) medium at a pH of 9.2, adjusted by using ammonium/ammonia (0.5 M) as a buffer solution. The linear concentration ranges are 30.0-100.0, 100.0-600.0, 50.0-150.0, and 30.0-100.0 ng/mL for salicylic acid, fenoprofen, diflunisal, and 6-methoxy-2-naphthylacetic acid, respectively, at lambda(ex)/lambda(em) = 281.1/423.6, 241.2/301.2, 284.1/403.8, and 268.7/339.6 nm, respectively. Analytical parameters of the proposed method were calculated according to the error propagation theory. The sensitivity, repeatability, reproducibility, and limits of detection achieved with the proposed method are adequate for the determination of these anti-inflammatory drugs.