A flow through analysis biosensor system for cyanide

A flow through biosensor system has been developed for the determination of free cyanide in brass plating and rinsing solutions. The system consisted of rhodanese immobilized on aminopropyl glass beads via glutaraldehyde activation to form an enzyme column and sulfite oxidase immobilized on a preactivated nylon membrane and attached to the surface of a hydrogen peroxide electrode (platinum vs silver/silver chloride at 0.7 V). The immobilized rhodanese first converted cyanide to thiocyanate in the presence of thiosulfate and produced sulfite which was, in turn, converted to sulfate by immobilized sulfate oxidase. The latter enzymatic reaction also released hydrogen peroxide which was amperometrically detected at the platinum anode. The biosensor system exhibited a linear response from 5 to 1000 μM cyanide and could be reused for 35 repeated analyses. The system was stable for at least 18 h of continuous operation at 25°C. The immobilized rhodanese and sulfite oxidase stored in 3 M ammonium sulfate were stable for 4 months at −20°C and 50 days at 4°C, respectively. When measuring cyanide in metal plating solutions, the results obtained by the biosensor system agreed well with that of soluble enzymatic and the colorimetric assays. The data obtained, however, was not in agreement to those of the commercially available Orion cyanide electrode.