The adaptation of a piezo-optical gas sensing system to detect copper ions in aqueous solution

A piezo-optical gas sensing system has been adapted to detect copper(II) ions in aqueous solution at pH 6.5 by using a thin polymer-bound film of powdered sol–gel silica doped with eriochrome cyanine R (ECR). Effects of varying ECR concentration, immersion time in the test solution, drying time and copper(II) concentration have been studied. The system permits rapid and inexpensive field measurements of copper(II) concentrations between 0.01 mM (0.6 ppm) and 0.5 mM (30 ppm) in water at pH 6.5, to an accuracy better than ±20%.