Spectroscopic study of dyes for pH and methanol sensing

The spectral response of three dyes, in both pH and methanol in strongly acidic environments as examples of the inner media of a proton exchange membrane such as Nafion, was investigated. Picric acid responded predominantly to pH while C.I. Acid Orange 5 and C.I. Basic Green 4 each gave a combined response to both pH and methanol concentration. The spectroscopic results obtained show the feasibility of using a single dye for measuring pH without significant interference from methanol; the simultaneous determination of pH and methanol concentration using a binary combination of dyes is also feasible. These characteristics of the dyes allow their use as primary transducers for a fuel concentration sensor in a direct methanol fuel cell.