Applicability of gallium as copper scavenger in the determination of zinc in samples of high copper content by potentiometric stripping analysis

Abstract

The determination of zinc in the presence of copper by potentiometric stripping analysis is hindered by the formation of Cu-Zn intermetallic compounds on the working electrode during the deposition step. An excess of gallium is usually added to the sample to prevent the formation of Cu-Zn by forming much more stable Cu-Ga intermetallics. If the Cu : Zn mass ratio is higher than about 5, only part of the analytical signal of zinc is restored after addition of gallium and both the precision and accuracy of the determination are reduced. A simple extraction procedure is recommended to remove the bulk of copper from the sample. The pH of the working sample solution is adjusted to 4 (0.5 M acetate buffer) and is extracted with half of its volume of a 3%V/V solution of acetylacetone in benzene. Each extraction removes about 80% of the copper present without affecting the zinc. The determination of zinc is subsequently carried out after adding Hg^II as an oxidant and gallium to mask the remaining copper. The method was applied to the determination of zinc in low-zinc, high-copper brass samples.