Increased Sensitivity and Selectivity for As(III) Detection at the Au(111) Surface: Single Crystals and Ultraflat Thin Films Comparison

Abstract

Electrochemical stripping voltammetry electroanalysis sensitivity and selectivity are oftentimes limited by wide variance in analyte electrode surface adsorption and desorption energies. The use of highly oriented Au(111) single crystal and thin film surfaces is shown to decrease this variance and improve detection for arsenic (As) in water. Cyclic voltammetry and linear stripping voltammetry (LSV) analysis on Au oriented and polyoriented electrode surfaces demonstrated that As deposition and oxidation is a complex surface-structure-dependent process. An electrochemical quartz microbalance indicated that As is deposited in multiple layers when in high concentrations and does not permanently reorganize the Au surface after stripping. LSV analysis of As(III) on the Au(111), Au(110), Au(100), and Au polyoriented single crystal, Au(Poly), model electrode surfaces showed that Au(111) had the highest peak to background ratio and narrowest peak width for As oxidative stripping. Furthermore, an ultraflat Au(111) thin film, Au(UTF), was then compared to the Au(111) and Au(Poly) single crystals and showed a bulk Au(111) single crystal-like response. The Au(UTF) was then used to perform a calibration curve to detect between 2.5 and 100 μg L–1 As(III) and resulted in a theoretical limit of detection of 0.0065 μg L–1 in 0.5 M H2SO4. The results from this study indicate that the Au(UTF) surface provides the sensitivity necessary for detection of trace concentrations of As in water at or below the maximum contaminant level (MCL) of 10 μg L–1.