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 electrodes into cysteine solutions. Such electrodes exhibit excellent sensitivity and selectivity toward copper(II) determination, because the bidentate chelation of amino acids toward copper(II) is effective and far superior than 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 dynamic range of 2 orders of magnitude (from 5.0 to 0.050 μg/L) and the detection limit is as low as 25 ng/L (0.39 nM). This method is applied to the determination of copper(II) in two reference materials, SLEW-2 (river water, 1.62 μg/L) and CASS-3 (seawater, 0.517 μg/L). The results agree satisfactorily with the certified values.