Spectrophotometric determination of arsenic via nanogold formation in micellar medium

Abstract

Colloidal gold nanoparticles are formed in aqueous anionic micellar medium by the qu antitative reduction of chloroauric acid (HAuCl₄) by arsine (AsH₃) gas produced from arsenic bearing sample water. The absorbance of the pink gold sol(λ_max at 530 nm) is a measure of arsenic concentration present in the sample .Both, As(III) and As(V) either present individually or in mixture could be determined. The molar absorptivity is 6.1×10³ lit mol^-1 cm^-1 and the Sandell sensitivity is 1.28×10^-2 μg cm^-2. The gold particles, as observed from the transmission electron microscopy analysis, are spherical in nature, the average size being 14±5 nm. The linear dynamic range (LDR) for the arsenic determination is 0-0.5 ppm (0-6 67×10^-6<i>M</i>)<i>. </i>The limit of detection (LOD) is 0.005 ppm. The 95% confidence limit for 0.2 ppm of arsenic is 0.207± 0.007 ppm (for 10 replicates). The relative standard deviation (RSD) is <±5%. The method is free from the common interferences, Fe²⁺/ Fe³⁺,Ca²⁺/Mg²⁺ PO₄^-3, SiO₃^-2 ,NO₃^-, Cl^-,SO₄^-2, humic acid, common herbicides/pesticides like 2, 4-D, endosulfan, atrazine, etc, and can be applied for the determination of total arsenic concentration in real water samples. The results are in good agreement with the SDDC method. The toxic and volatile organic solvents used for silver diethyldithiocarbamate method could be avoided in this method and hence it is safer, much easier and more reproducible.