POLAROGRAPHIC MODES CAPABLE OF DISCRIMINATING BETWEEN REVERSIBLE AND IRREVERSIBLE-PROCESSES

A commercially available polarographic instrument incorporates novel m ethodology designed to enhance the response of reversible analytes ove r that of interfering irreversible analytes, or vice versa. The princi ple involved is to sample the current flowing in response to a potenti al pulse at two different times. These two samples are then combined i n two alternative ways: either to discriminate against an irreversible process (the DPR mode), or to discriminate against a reversible proce ss (the DPI mode). The theory underlying these discriminatory modes ha s been developed and used to predict their efficiency. These predictio ns have been compared with experimental results for the reduction of t he Cd2+, Zn2+ and Ni2+ ions at a mercury drop electrode, using a Metro hm instrument capable of implementing the DPR and DPI modes, in additi on to the usual DPN (single current sample) mode of differential pulse polarography. There is qualitative agreement between theory and exper iment, and both serve to validate the principle. The effectiveness of the DPR mode against the irreversible reductions of H- and dissolved 0 2 is also examined.