Application of cysteine monolayers for electrochemical determination of sub-ppb copper(II)

Electrodes with the functionality of amino acids can be easily prepared by taking advantage of strong sulfur-gold interactions and immersing gold elec trodes into cysteine solutions. Such electrodes exhibit excellent sensitivi ty and selectivity toward copper(II) determination, because the bidentate c helation of amino acids toward copper(II) is effective and far superior tha n that toward any other metal ions. In this study, we demonstrate that at a preconcentration time of 5 min the cysteine-modified electrode has a dynam ic range of 2 orders of magnitude (from 5.0 to 0.050 mu g/L) and the detect ion limit is as low as 25 ng/L (0.39 nM). This method is applied to the det ermination of copper(II) in two reference materials, SLEW-2 (river water, 1 .62 mu g/L) and CASS-3 (seawater, 0.517 mu g/L). The results agree satisfac torily with the certified values.