Zeolite/polymer-modification of a mercury electrode. Effects on the Cu2+ interference in the stripping determination of Zn2+

The present study was carried out in order to investigate whether zeolite 1 3X (aperture 7.4 Angstrom) modification of a mercury electrode could provid e discrimination against the interference from Cu2+ the stripping determina tion of Zn2+ (utilizing the zeolite ion exchange capability, and the possib ility for small differences in size and shape of hydrated Zn2+ and Cu2+ and hence the differences in zeolite affinity to these species). For this purp ose a chemically modified electrode (CME) was constructed from a glassy car bon electrode, which was first coated with a zeolite 10X containing polymer matrix then subjected to mercury plating. The analytical characteristics o f the CME were subsequently compared with those of a conventional thin merc ury film electrode (TMFE). The comparison, which was based on analogous str ipping experiments carried out using first the TMFE, then the CME, showed t hat stripping signals for Zn2+ as well as Cu2+ were obtained with both elec trodes. However, the intermetallic compound interference observed for the C ME Zn-response was much less pronounced than that encountered for the TMFE Zn-response, thus indicating that the zeolite modification provided a marke d discrimination towards deposition of Cu2+. Subsequent standard addition e xperiments with 60 s depositions at - 1200 mV revealed that the Zn-strippin g signal obtained with the CME was linear for 0-3.5 mu M Zn2+ in the presen ce of 10 mu M Cu2+.