Application of multivariate optimization procedures for preconcentration and determination of Au(III) and Pt(IV) in aqueous samples with graphene oxide by X-ray fluorescence spectrometry.

A simple method was developed for the determination of Au(III) and Pt(IV) contents in aqueous samples after preconcentration. The method was based on the sorption of analytes as 2-amino-5-mercapto-1,3,4-thiadiazol complexes onto graphene oxide and subsequent direct determination by wavelength dispersive X-ray fluorescence (WDXRF). The optimization step was carried out using two-level full-factorial and Box-Behnken designs. The effects of four variables (pH, ligand mass, sonication time, and temperature) were studied by a full-factorial design to find significant variables and their interactions. Results of two-level full-factorial design for Au extraction showed that the factors: pH, ligand mass, temperature of sonication beside the interaction of pH-ligand mass, and interaction sonication temperature-ligand mass were significant. For Pt, the results revealed pH, ligand mass, sonication time, and interaction of pH-ligand mass were statistically significant. Box-Behnken matrix design was applied to determine the optimum level of significant parameters for extraction of two analytes simultaneously. The optimum values of the factors were pH 2.5, 0.9 mL ligand solution, 56 min sonication time and 15 °C temperature. The limits of detection (LOD) were found to be 8 ng mL(-1) for Au and 6 ng mL(-1) for Pt. The adsorption capacity for Au and Pt were 115 and 169 μg mg(-1), respectively. The relative standard deviation (RSD) was lower than 1.4 % (n = 5), and the extraction percentage was more than 95 % for both elements. The method was validated by determination of Au and Pt in spiked water samples and certified reference standard materials.