Diamond Thin-Film Electrodes for Monitoring Heavy Metal Ions in Water Supplies Using Anodic Stripping Voltammetry 2005-01-2888

Conductive diamond is a new electrode material that functions well in anodic stripping voltammetry (ASV); a technique used for the determination of heavy metal ions in aqueous media. Work to adapt a previously developed ground-based method for targeted use onboard the International Space Station (ISS) is the subject of this paper. It is demonstrated that increasing the solution pH from 4.5 to 5.2 (a value near that acceptable for on-board use) did not cause significant alteration in the detection figures of merit for five priority metal ions (Ag(I), Cu(II), Pb(II), Cd(II) and Zn(II)). It is also shown that the addition of Ca(II) and Mg(II) salts at concentrations identical to those presently used in the potable water caused less than a 4% change in the signal obtained for most of the priority metal ions tested. Finally, elimination of the deoxygenation step (nitrogen purge) did not affect the signals for Ag(I) and Cd(II), but did cause a decrease in the signals for Pb(II) and Cu(II). Even with the decreased signals, though, a linear calibration curve was still obtained for Pb(II) with a detection limit of 50 ppb. The long-term electrode response stability for Cd(II) is also reported on. The signal remained constant (RSD ~5%) over a period of several weeks. The method was applied to the analysis of Ag(I) in simulated potable and technical water samples. Analysis of Ag(I) in the potable water sample yielded a result of 430 ± 2 ppb, which is within 2% of the expected value of 422 ppb. Analysis of Ag(I) in the technical water sample yielded a result of 530 ± 16 ppb, which is 9% higher than the expected value of 480 ppb.