The application of reverse pulse amperometry (RPA) at a polarographic detector in a flow-injection system or in cation-exchange chromatography (CEC) allows accurate monitoring of trace metal ions in a fluid stream without the conventional requirement of deaeration. The technique of RPA is based on the alternate application of two fixed potentials to a Hg electrode with a large negative initial potential, E(,i), for the reduction of the analyte as well as dissolved oxygen, followed by a short positive pulse to the final potential, E(,f), for the oxidation of the reduced form of the analyte. Since the reduction products of oxygen, i.e., H(,2)O(,2) and H(,2)O, are not reoxidized at the positive potential, E(,f), due to their characteristic irreversibility, the analytical signal measured at E(,f) is free of interference from dissolved oxygen;The metal ions studied were classified based on the nature of the reactions taking place at E(,i) and E(,f). The different responses for the different classes of metal ions were correlated to the derived equations of response for RPA. The operational parameters for RPA at a polarographic detector in a fluid stream, including the drop time, the initial potential, and the flow rate, were optimized. Satisfactory separation of a mixture of six transition and heavy metal ions (Cu('2+), Zn('2+), Ni('2+), Pb('2+), Cd('2+) and Fe('2+)) was achieved by CEC with the complexing agent sodium tartrate present in the eluent. The effects of pH and concentration of the eluent, as well as the effect of the concentration of Mg('2+) in the eluent, on the retention time was investigated. The feasibility of applying RPA at a polarographic detector as a means of detection for CEC was demonstrated by analysis of real samples including: NBS SRM la argillaceous limestone, ground water, and power plant water from the campus of Iowa State University. The approximate detection limit (S/N = 2) for Cu('2+) and Zn('2+) in CEC was 64 ppb and 13 ppb, respectively.