Abstract: A synchronous fluorescence spectrometry combined with first order derivative has been developed for the simultaneous determination of methylene blue (MB) and azure A (AA). The method is based upon the formation of ion-association complexes of AuCl4- with MB and AA and solvent extraction of the two complexes by 1,2-dichloroethane in aciditive medium. When [MB][AuCl4]3 and [AA][AuCl4]2 complexes were synchronously scanned at Δλ=20 nm with first order derivative techniques treatmented in organic phase, the derivative-synchronous fluorescence peaks appeared at 685 nm for [MB][AuCl4]3 and 610 nm for [AA][AuCl4]2, respectively. The fluorescence intensities were directly proportional to the concentrations of MB at 685 nm and AA at 610 nm within certain range. So, a simple, sensitive method has been developed for the simultaneous determination of MB and AA. The detection limit (3σ) and linear range were 7.90 ng mL-1 and 0.03-4.80 μg mL-1 for MB, 17.8 ng mL-1 and 0.06-5.80 μg mL-1 for AA. In this work, the spectral characteristics and composing of ion-association complexes, the optimum conditions and the influences on reaction system were investigated. The method can be applied to the simultaneous determination of AA and MB in urine samples and in Azure II with satisfactory results.

Key words: derivative-synchronous fluorescence spectra, simultaneous determination, Methylene blue, Azure A, Solvent extraction