Cathodic stripping voltammetric determination of ultratrace gold(iii) at a bulk modified epoxy–graphite tube composite electrode in flow systems

An epoxy-impregnated graphite tube composite electrode bulk modified with 2-mercaptobenzoxazole was fabricated and employed for the determination of gold. A differential-pulse cathodic stripping procedure in conjunction with either continuous flow or flow injection was developed. Both open and closed circuit accumulation of Au(iii) were investigated. The addition of Rhodamine 6G to the accumulation medium enhanced the sensitivity. Factors influencing the analysis were optimized. For continuous flow, precisions were 6.33% [relative standard deviation, n = 6, 5.00 3 1028 m Au(iii), accumulation 10 min, open circuit] and 7.06% [n = 6, 1.00 3 1029 m Au(iii), accumulation 10 min, closed circuit]. The detection limits (S/N = 3) were 6.7 3 1029 and 1.9 3 10210 m Au(iii) for open and closed circuit accumulations, respectively, with 10 min accumulation. For flow injection under similar conditions, the detection limits were 3.1 3 1027 m Au(iii) (open circuit, injection volume 500 ml, 30.5 ng injected) and 2.9 3 1029 m (closed circuit, injection volume 500 ml, 0.29 ng injected). Selected metal ions and other inorganic and organic substances were examined for interferences. The developed method was applied to a certified water sample (US EPA WP 386), a sea-water sample and a pin-connector sample.