STUDIES ON THE RESPONSE OF POTENTIOMETRIC SENSORS AND THE CHARACTERIZATION OF REACTIVE IMPURITIES IN PROPYLENE CARBONATE AND GAMMA-BUTYROLACTONE AS SOLVENTS

This article deals with an experimental protocol developed to characterize reactive impurities that seriously compromise the utility of relatively inert solvents such as those discussed. It was found that potentiometric sensors for hydrogen, silver(I), and copper(II) ions give Nernstian response over a broad activity range in solutions of widely differing buffer capacity in gamma-butyrolactone (GBL), a promising but inadequately explored solvent for a variety of applications. Advantage was taken of the proper response of these sensors in applying the ''ion probe method'' described before to characterize impurities in both unpurified and purified gamma-butyrolactone on the basis of their reactivities rather than their concentrations alone. The same sensors were also used in conventional potentiometric titrations of impurities in propylene carbonate (PC), a solvent that has been extensively used in fundamental studies of solute-solvent interactions as well as in the construction of commercial lithium batteries. The results of the potentiometric studies served as a guide in the design of appropriate gas chromatographic measurements. Three impurities not reported before were found in a reagent grade propylene carbonate: triethylamine and chloride ion, both at concentrations above 10(-4) M, as well as 1,2-dibromopropane. The effectiveness of different purification procedures was studied.