Catalytic determination of traces of Rh(III) using an optode based on immobilization of methyl violet on a triacetylcellulose membrane

The characterization of an optical sensor membrane is described for determination of rhodium. The optode sensing reagent is methyl violet which is immobilized on triacetylcellulose membrane. It has been found that oxidation of methyl violet with periodate is very slow. Presence of trace amount of Rh(III) catalyzes the reaction and causes a significant increase in the reaction rate. The reaction of periodate with the immobilized methyl violet in the presence of rhodium in acidic media causes a decrease in the absorbance of the film at 594 nm which is directly proportional to the concentration of rhodium. This sensing phase has a linear range of 1-110 μg mL⁻¹ for Rh(III) ions. The one-shot sensor can readily be fully regenerated with methyl violet solution, and the color is fully reversible.