Sulfite determination using sulfite oxidase biosensor based glassy carbon electrode coated with thin mercury film

The preparation of sulfite biosensor by immobilization of sulfite oxidase on a glassy carbon electrode coated with mercury thin film is described. Dissolved oxygen can be readily reduced at the glassy carbon electrode coated with mercury thin film. The working principle of the biosensor was based on monitoring decrease in the peak current due to the depletion in dissolved oxygen concentration according to the reaction of sulfite oxidase.The biosensor allowed a low working potential of −0.24 V vs. Ag/AgCl. Immobilization parameters such as sulfite oxidase activity, gelatin amount, and glutaraldehyde percentage were investigated. The pH optimum of 7.0 was found when using phosphate buffer. Appropriate buffer concentration was found to be 0.05 M. Working temperature was accepted as 40 °C. The biosensor was stable at 40 °C for 3 h without loss of its initial activity. The calibration graph for the biosensor was linear between the concentration ranges of 2 × 10−4–2.8 × 10−3 M sulfite. The results of sample analyses obtained with the biosensor agreed well with the enzymatic-spectrophotometric reference method.