Simultaneous determination of acetylsalicylic and salicylic acids in human serum and aspirin formulations by second-derivative synchronous fluorescence spectrometry.

A second-derivative synchronous scanning spectrofluorimetric method for the simultaneous determination of acetylsalicylic acid (ASA) and salicylic acid (SA) is described. The method is based on the native fluorescence of both acids in a 1% acetic acid-chloroform solution. Both ASA and SA can be determined within the concentration ranges 0.2-70 and 0.03-10 micrograms ml-1, respectively. The effect of each acid on the signal of the other has been studied in detail. Empirical equations have been used to overcome this effect, thus allowing the accurate determination of both acids in binary mixtures, without a separation step. The method has been applied to the determination of ASA and SA in blood serum and to the determination of SA impurities in aspirin formulations. Recoveries from sera spiked with both ASA (2.5-50 micrograms ml-1) and SA (100-160 micrograms ml-1) varied from 99.5 to 106.7% (mean = 102.6%) and from 93.0 to 98.0% (mean = 95.8%), respectively. Recoveries of SA from spiked aspirin solutions (0.25-1.5 mg g-1 of aspirin) varied from 98.0 to 102.0% (mean = 100.3%).