THEORETICAL EVALUATION OF OPTICAL-RESPONSE TO CATIONS AND CATIONIC SURFACTANT FOR OPTRODE USING HEXADECYL-ACRIDINE ORANGE ATTACHED ON PLASTICIZED POLY(VINYL CHLORIDE) MEMBRANE

An optrode selective to potassium ions is constructed using a poly(vinyl chloride) (PVC) membrane and a positively charged fluorescent dye sensitive to polarity. Potassium ions in an aqueous solution are selectively extracted into the membrane, and the dye moves toward the aqueous solution by ion exchange with potassium ions. This concerted reaction causes an increase of polarity around the dye, resulting in the optrode response. A theoretical response curve, which agrees fairly well with the experimental result, is calculated based on the proposed mechanism. The optrode does not respond directly to a cationic surfactant, but the sensitivity of the optrode to potassium ions decreases with an increase of the concentration of the cationic surfactant. Thus the cationic surfactant can be measured by the potassium-ion optrode. This interference response is ascribed to a decrease in the extraction rate constant of potassium ions. The interference response is calculated based on this mechanism, and agrees well with the experimental result. The response of the optrode to anionic and non-ionic surfactants is investigated in detail, and a similar interference response is found for a non-ionic surfactant.