Application of the interfacial instability to chemical sensors. The simultaneous monitoring of high concetrations of hydrogen ions and sulfate ions

Abstract

The authors have proposed a new method of measuring hydrogen ions and sulfate ions in concentrated acids by using passivation and depassivation phenomena. The basic idea underlying this method is that the chemical composition of a solution sensitively reflects the stability of the solid/liquid interface. In the present study, the authors have demonstrated that the passivation-depassivation phenomena of iron could be applied to the determination of the concentrations of hydrogen ions and sulfate ions simultaneously and separately by the following processes. Passivation time τ is a function of the concentrations of hydrogen ions and sulfate ions, and anodic current density. The contour lines of τ between hydrogen ions and sulfate ions can be drawn when anodic current density is maintained constant. Depassivation time t F is a sole function of the concentration of hydrogen ions. Therefore, the measurement of t F determines the concentration of hydrogen ions. The concentration of sulfate ions can be determined by combining the contour lines of τ and t F.