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 respect to their suitability for speciation of lead in the presence of humic acid (HA). The antifouling coating (0.5 mu m thick) on the PI-TMFE was deposited by electrostatic spraying, and the permeability was controlled by a novel resolvation procedure. The detection method was differential pulse anodic stripping voltammetry. The response of the TMFE was so strongly influenced by adsorption of IIA that it did not provide a meaningful estimate of the degree of complexation of lead in the bulk solution. Addition of KA was accompanied by a drift of the lead peak current from which it could be inferred that the adsorption effect increased the signal at pH 4.6 but lowered it at pH 2.7. Furthermore, the TMFE showed a strong memory effect when it had 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 current when HA was added at pH 4.6 and 2.7 correlated well with the bulk complexation of lead. The PI-TMFE is therefore superior to the TMFE for studying the speciation of metal ions in the presence of HA.