Cathodic stripping voltammetric determination of ultratrace gold(III) at abulk 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 clos ed circuit accumulation of Au(III) were investigated. The addition of Rhoda mine 6G to the accumulation medium enhanced the sensitivity. Factors influe ncing the analysis were optimized. For continuous flow, precisions were 6.3 3% [relative standard deviation, la = 6, 5.00 x 10(-8) M Au(III), accumulat ion 10 min, open circuit] and 7.06% [n = 6, 1.00 x 10(-9) M Au(III), accumu lation 10 min, closed circuit]. The detection limits (S/N = 3) were 6.7 x 1 0-9 and 1.9 x 10(-10) M Au(III) for Open and closed circuit accumulations, respectively, with 10 min accumulation. For flow injection under similar co nditions, the detection limits were 3.1 x 10(-7) M Au(III) (open circuit, i njection volume 500 mu l, 30.5 ng injected) and 2.9 x 10-9 hi (closed circu it, injection volume 500 mu l, 0.29 ng injected). Selected metal ions and o ther 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.