Development of a rapid and highly sensitive plasticized PVC membrane Optode utilizing an ionic liquid material composed of bromothymol blue

Abstract

In this work, ionic liquid materials composed of pH indicator dyes were synthesized and used as a plasticizer for a plasticized PVC membrane-based ion-selective optode. We chose several triphenylmethane dyes and synthesized ionic liquids with those by an ion-exchange procedure, and found that an ionic liquid composed of bromothymol blue (BTB) realized the highest ion-exchange ratio of approximately 100% (highest concentration of dye). The absorbance response of the PVC membrane using a BTB-based ionic liquid was decreased by ca. 37% using the repetitive introduction of acid and base solutions, and reached to exhibit a stable and reproducible response. The concentration of dye was 20~70-times higher than that of the conventional ones. In addition, the PVC membrane was applied for anion sensing based on the coextraction of protons and anions in aqueous solutions, and it was found that the ion selectivity followed the Hofmeister series. In the future, the present ionic liquid material is expected to be applied for highly-selective and sensitive ion-selective optodes by the modification of functional groups such as ion-recognition or reaction with the target molecule.