Determination of three aspirin metabolites in human urine by derivative synchronous spectrofluorimetry

Abstract

The direct and simultaneous determination of three aspirin metabolites present in human urine (salicylic acid, salicyluric acid and gentisic acid) is described. The method involves the measurement of synchronous fluorescence spectra (Δλ= 100 nm) of untreated urine samples at a single pH (borate buffer giving pH 9.0). The combination of first- and second-derivative spectra and the zero-crossing technique allows calibration plots for the three metabolites to be obtained that are linear in the range 0.02–0.2 ppm. The solution of a system of three simultaneous linear equations is discussed. Better results are obtained by transferring the second-derivative spectra in the range λ_exc= 325–375 nm to a microcomputer and performing a least-squares fit of the sample to a combination of spectra of three standard solutions. This choice of wavelengths makes it unnecessary to eliminate normal fluorescent urine components.