Purification of pyridine for voltammetric studies : Effect of impurities

Abstract

Purification of pyridine by zone fractional crystallization reduces the concentration of prewave-producing contaminant below polarographic detection limits, i.e., 0.01 mM. A qualitative test based on the stability of the free radical diphenylpicrylhydrazyl has shown the method to be capable of reducing the concentration of proton-releasing impurities. Water is also removed. Investigation of the effect of the contaminants in normal reagent-grade pyridine on the electrocapillary curves and polarograms of pyridine solutions containing lithium perchlorate and tetraethylammonium perchlorate as background electrolytes in the presence and absence of oxygen, has indicated that the impurities are capable of changing the mechanism for the electrochemical reduction of oxygen in pyridine.