Determination of the ion-pair constant between chloride ion and cationic-coated, silver SERS substrates using competitive complexation

The interaction of chloride ion with cationic-coated silver surface-enhance d Raman scattering (SERS) substrates was monitored using a competitive comp lexation technique. In this approach, the nitrate concentration is kept con stant and the chloride ion concentration is varied. The change in the nitra te peak area, Delta A(NO3), is measured as a function of chloride ion conce ntration, Gel. The measured response is described by the following relation ship: Delta A(NO3) = VCCl/(K + C-Cl). Using the value of K and the value of the ion-pair constant between the cationic coatings and nitrate ion, it is possible to extract the value of the ion-pair constant for chloride ion. T he selectivities of the cationic coatings for nitrate, sulfate, and chlorid e ions are discussed.