INVESTIGATION OF MERCURY FREE POTENTIOMETRIC STRIPPING ANALYSIS AND THE INFLUENCE OF MERCURY IN THE ANALYSIS OF TRACE-ELEMENTS LEAD AND TITLE

The application of Potentiometric Stripping Analysis (PSA), without an y mercury, to the determination of trace elements lead and zinc, resul ts in linear responses between stripping-peak areas and concentrations within 0 to 2000 ng/g. The best response, as determined by the size o f stripping areas, was obtained with an electrode prepared with mercur y but without mercury ions in the electrolyte. Lead is analysed by a f reshly polished glassy-carbon electrode in 0.09 - 0.1 mol/L HCl while the analysis of zinc requires an electrode activation procedure. The e lectrode activation is performed by stripping zinc in an electrolyte c ontaining 0.1 mol/L HCl and 2 mu g/g Zn2+ and electrolysis at -1400 mV (SCE). The concentration range of linear response occurs where the el ectrode is not fully covered by metal clusters during the electrolysis step. The influence of mercury is investigated and a model is propose d which explains the co-deposition of mercury and test metals in the e lectrolysis step in terms of a charge-distribution parameter. The mode l explains that the decrease of stripping peak area, as a function of concentration, is entirely due to mercury ions being simultaneously re duced together with the ions of the test metal in the electrolysis ste p. The influence of hydrogen evolution and oxygen reduction together w ith possible improvements of the method are discussed.