Simultaneous Determination of Nickel and Cadmium by Differential Pulse Polarography

Abstract

Spent nickel-cadmium batteries have become an environmental inconvenience, and many efforts have been undertaken to treat or dispose of them in a safe way. 1,2 Research has been performed for the selective electrodeposition of nickel and cadmium from simulated waste solutions. 3 Work is being carried out in our laboratory with a similar objective. There is an obvious need to analyze both metal concentrations simultaneously and continuously with a fast and precise analytical method in the concentration range of interest. Whereas cadmium is not normally an analytical problem, many different analytical techniques have been proposed for the analysis of Ni, such as spectrophotometry, 4-9 9 atomic absorption, 10,11 flame emission, 12,13 and ion exchange. 14 However, most of these require pieces of somewhat expensive equipment and time-consuming sample preparation procedures. The electrochemical analysis of small amounts of nickel requires relatively inexpensive equipment but presents certain difficulties due to its irreversible reduction behavior. 15,16 In spite of this, it has been successfully accomplished using a variety of techniques such as stripping and voltammetric analysis, 17-22 polarography, 16,23-27 and potentiometry, 28 To the best of our knowledge, the simultaneous analysis of Ni and Cd by differential pulse polarography has not been reported yet. The present work reports on the conditions found suitable to perform such an analysis in the same matrix by slow sweep differential pulse polarography on a controlled-growth mercury electrode (CGME) in the concentration range of 10 -4 to 10 -5 M for both species. In addition to the simplicity of the analytical procedure, the transfer of the analyte to the polarographic cell is straightforward and does not require a special preparation protocol. The precision obtained in the Ni analysis is similar to, or even higher than, that of most of the procedures mentioned earlier, and that of Cd is also found to be very high.