Second-derivative synchronous fluorescence spectroscopy for the simultaneous determination of naproxen and salicylic acid in human serum

Second-derivative synchronous fluorescence spectrometry was used to develop a simple, rapid and sensitive spectrofluorimetric method for the simultaneous determination of naproxen and salicylic acid in human serum. The method is based on the intrinsic fluorescence of naproxen and salicylic acid in chloroform-1% acetic acid solution. A Delta lambda of 130 nm was used for the direct measurement of salicylic acid in the binary mixture, whereas naproxen was determined from direct measurements at Delta lambda = 60 nm and by means of a correction equation which incorporates the concentration of salicylic acid. The range of application is 0-14 mg l(-1) for naproxen and 0-13 mg l(-1) for salicylic acid. The detection limits for naproxen and salicylic acid are 0.003 and 0.01 mg l(-1), respectively. Serum samples are extracted into chloroform-1% acetic acid solution prior to instrumental measurement. Analytical recoveries range from 97 to 105% (mean 102%) for naproxen and from 97 to 112% (mean 103%) for salicylic acid. The within-run precision (RSD) for the method for four naproxen-salicylic acid mixtures varied from 1.2 to 6.7% and the day-to-day precision for mixtures varied from 2.1 to 5.0%.