Amperometric sensing of sulfite using a gold electrode coated with ordered mesoporous carbon modified with nickel hexacyanoferrate

An amperometric sulfite sensor was fabricated based on nickel hexacyanoferrate (NiHCF) electrodeposited on a layer of ordered mesoporous carbon covering on a gold electrode surface (NiHCF/OMC/Au). The prepared NiHCF/OMC/Au displayed good electrocatalytic activity towards the oxidation of sulfite. The sulfite response was determined at an optimal applied potential of 0.40 V vs Ag/AgCl in a flow injection analysis system. Under optimum conditions, the sensor has a linear response in the 2.5 mu M to 50 mM sulfite concentration range and a 2.5 mu M limit of detection (at an S/N ratio of 3). The electrode has a high operational stability, can be used up to 104 times (with a RSD of 5.9%), and a good electrode-to-electrode repeatability (with an RSD of <7.0%, for n = 6). It was applied, in the flow injection mode, to analyze sulfite in vermicelli, instant noodles, noodles, and macaroni. Recoveries of spiked samples ranged of from 80 +/- 1 to 108 +/- 2%, and the results agreed well with the Monier-Williams AOAC official method.