Optimization and simultaneous spectrophotometric determination of Thiosulfate and Sulfite in water samples based on insitu formation of AuNPs using PLSR

Sulfite and thiosulfate are two reducing agents which have been extensively used in many industries for different purposes and as any other chemical pollutant in environment, intake of excess amounts of them can cause severe health problems. So various analytical methodologies have been employed for their determination in environmental samples [1, 2]. AuNPs present interesting optical properties due to their strong SPR absorptions in visible region of spectrum and their stability and ease of preparation. An interesting application in this field is the employment of reducing nature of analytes for insitu reduction of gold ions in solution and formation of AuNPs which can be used as colorimetric sensors for analyte determination [3- 5]. On the other hand, development of accurate and precise analytical methodologies for optimization and simultaneous multicomponent determination in analyzed samples has an undeniable importance which can be fulfilled by chemometrics especially in the case of spectroscopic data which usually have a well-defined bilinear behavior. In the present study, Partial Least Squares Regression has been used for simultaneous determination of thiosulfate and sulfite in water samples based on the redox reaction of analytes with Au(III) ions in the presence of SDS as surfactant and formation of AuNPs in solution which exhibit SPR absorptions proportional to the analyte concentration. The effects of various parameters on the formation of AuNPs including pH, time and concentrations of Au(III) and SDS have been studied and optimized using a four factor Central Composite Design. The spectra of samples were taken in ranges 400-800 nm with 1 nm intervals. Analytical figures of merit have been investigated and Beer’s law obeyed over the concentration range 4*10-5–1.6*10-4 mol. L-1. The accuracy of method has been confirmed by recovery experiments.