A High-Performance Liquid Chromatographic Method for the Quantitative Determination of Naproxen and Des-Methyl-Naproxen in Biological Samples

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Abstract
A HPLC method for the quantitative analysis of naproxen and its major metabolite des-methyl-naproxen in biological fluid samples is described. Two methods of detection are compared: U.V. spectrophometry and spectrophotofluorometry. In both procedures an internal standard is used: diflunisal in the U.V. procedure and the ethoxy-analog of naproxen during fluorometry. The sensitivity of the fluorometric detection is higher than that of the U.V. detection; the limit being respectively 0.1 μg and 2.0 μg per milliliter sample. The fluorescence detection procedure can also be applied to very small samples (0.05 ml) in the therapeutic concentration rang range. Both procedures have been applied to clinical and laboratory studies in which they appear to be very satisfactory because of their ease of handling and their suitability for routinely performed analysis.