Determination of low levels of cadmium ions by the under potential deposition on a self-assembled monolayer on gold electrode

The electrochemical determination of low levels of Cd using a self-assembled monolayer (SAM) modified Au electrode is reported. Determination was based on the stripping of Cd, which was deposited by under potential deposition (UPD). A series of short alkanethiol SAMs bearing different end groups, i.e., sulfonate, carboxylate and ammonium, were examined. Lowest level of detection (ca. 50ngL^-1) was achieved with a 3-mercaptopropionic acid (MPA) monolayer using subtractive anodic square wave voltammetry (SASV). Additional surface methods, namely, reductive desorption and X-ray photoelectron spectroscopy, were applied to determine the interfacial structure of the electrodeposited Cd on the modified electrodes. We conclude that the deposited Cd forms a monoatomic layer, which bridges between the gold surface and the alkanethiol monolayer associating with both the gold and the sulfur atoms.