Alternating Current Polarographic Method of Analysis in the Presence of Oxygen and Other Irreversibly Reduced Species

The influence of irreversible alternating current electrode processes on the analytical applications of ac polarography to the determination of reversibly reduced/oxidized electroactive species has been shown to be extremely important. In particular, the influence of oxygen with respect to the frequently reported advantage that ac polarography can be carried out without degassing to remore irreversibly reduced oxygen has been examined in detail to find conditions in which to best utilize this advantage in a general manner with comparable results to degassed solutions. The presence of oxygen is shown to interfere in two ways, (a) The product of the electrode process, hydroxide ion, can interact with electroactive species reduced at more negative potentials, (b) The presence of the ac oxygen wave itself is important and decreases the limit of detection. From this investigation, it was shown that a highly acidic medium such as 5M HCl is the most satisfactory medium to use in ac polarography if degassing is to be eliminated. Interference (a) is virtually eliminated in this medium and with only interference (b) present, the method can be used reliably down to concentrations of about 10^–5M with comparable precision to degassed solutions. The effect of irreversibly reduced iron on the determination of tin and other elements is also reported; unlike oxygen, interference is not readily removed.