Evaluation of copper(II) eriochrome cyanine R (ECR) complex immobilized in anion exchange membrane as a potential nitric oxide optical sensor

The immobilization of the copper(II) complex of Eriochrome cyanine R (Cu(ECR)(2)) in anion exchange membranes was investigated in the development of an optical sensor for nitric oxide (NO) gas. The change in the absorbance spectrum of Cu(ECR)(2) membranes was monitored at 445 nm on exposure to NO gas and a steady- state response was obtained following a 400 s exposure time. This response was highly linear (r(2) = 0.996) up to 6 ppm NO and the detection limit was calculated to be 0.848 ppm (similar to 28.28 mu M in solution). This response was 4.7 times more sensitive to changing NO gas concentrations (0-6 ppm) compared with that of Cu(ECR) 2 immobilized in silicone rubber films. This response was fully reversible by resubmersion of the membranes in copper(II) solution following NO exposure and this reversibility was extremely reproducible (0.81%, relative standard deviation, n= 3). These anion exchange membranes were more selective to NO gas rather than O-2 (80: 1), NO2 (3: 1), and CO (7: 1) and these gases were shown not to interfere with the reaction of Cu- ECR membranes with NO itself.