PH AND IONIC-STRENGTH DEPENDENCE OF THE ASV RESPONSE OF CADMIUM, LEAD AND ZINC IN SOLUTIONS WHICH SIMULATE NATURAL-WATERS

Anodic stripping voltammetry (ASV) peak currents of Pb, Zn and Cd (5 .times. 10-8 M) in low ionic strength (1mM), bicarbonate-buffered solutions were suppressed by increasing the pH (range 4-8). Increasing the ionic strength (1-500 mM) of Pb solutions reduced the pH-dependent response, especially when NaClO4 rather than KCl was used as the supporting electrolyte. At low ionic strengths and pH > 6, Pb solutions showed a broadened or double peak indicating an alternative oxidation mechanism. Use of NaCl as a supporting electrolyte showed that the cation controlled the current. This and other evidence, such as the time-dependent response, indicates that low currents were due to adsorption of trace metal onto the cell assembly. The inability to predict pH and ionic strength dependent changes of stripping currents measured in simple inorganic solutions illustrates the many problems associated with using ASV for speciation studies on untreated natural waters which contain extremely low concentrations of trace metals.