On-Site Analysis of Arsenic in Groundwater Using a Microfabricated Gold Ultramicroelectrode Array

Rosemary Feeney and Samuel P. Kounaves*
Department of Chemistry, Tufts University, Medford, Massachusetts 02155

     Rapid on-site analysis of arsenic in groundwater was achieved with a small battery-powered unit in conjunction with a microfabricated gold ultramicroelectrode array (Au-UMEA).  The sensor, consisting of 564 UME disks and  providing a unique gold surface created by electron beam evaporation, was demonstrated to be highly sensitive to low-ppb As³⁺ using square wave anodic stripping voltammetry.  The influence of the square wave frequency, pulse amplitude, and deposition potential on the arsenic peak stripping current was investigated.  Varying those theoretical parameters yielded results surprisingly similar to those for the thin Hg film case.  The performance of the Au-UMEA was evaluated for reproducibility and reliability.  Three stability tests showed an average relative standard deviation of 2.5 % for 15 consecutive runs.  Limits of detection were investigated, and 0.05 ppb As³⁺ could be measured while maintaining a S/N of 3:1.  Interference studies were performed in the presence of 50-500 ppb of Cu²⁺, Hg²⁺ and Pb²⁺.  On-site analysis of groundwater containing arsenic was performed with a small battery-powered potentiostat.  Quantification was done through standard additions, and these results were compared to the standard EPA methodology.