Comparative study of conventional and cellulose acetate-coated mercury film electrodes for speciation of lead in the presence of humic acid

A conventional thin mercury film electrode (TMFE) and a TMFE coated with a phase-inversion cellulose acetate membrane (PI-TMFE) were compared with res pect to their suitability for speciation of lead in the presence of humic a cid (HA). The antifouling coating (0.5 mu m thick) on the PI-TMFE was depos ited by electrostatic spraying, and the permeability was controlled by a no vel resolvation procedure. The detection method was differential pulse anod ic stripping voltammetry. The response of the TMFE was so strongly influenc ed by adsorption of IIA that it did not provide a meaningful estimate of th e degree of complexation of lead in the bulk solution. Addition of KA was a ccompanied by a drift of the lead peak current from which it could be infer red that the adsorption effect increased the signal at pH 4.6 but lowered i t at pH 2.7. Furthermore, the TMFE showed a strong memory effect when it ha d been exposed to HA which indicated that the adsorption was irreversible. In contrast, none of these symptoms of the adsorption of HA on the mercury surface were observed at the PI-TMFE, and the decrease in the lead peak cur rent when HA was added at pH 4.6 and 2.7 correlated well with the bulk comp lexation of lead. The PI-TMFE is therefore superior to the TMFE for studyin g the speciation of metal ions in the presence of HA.