FLOW-INJECTION AMPEROMETRIC DETERMINATION OF CYANIDE ON A MODIFIED SILVER ELECTRODE

A composite coating based on a mixture of phosphatidylcholine, cholesterol and stearic acid was used for fabricating a silver-based amperometric sensor. The sensor was used in a flow injection (Fl) configuration for the selective and sensitive determination of cyanide. The method is based on the permselectivity of the lipid membrane, which rejects from the surface of the working silver electrode the undesired, potentially interfering species, while allowing the transport of the analyte as hydrogen cyanide. Logarithmic calibration graphs were linear up to the maximum concentration of CN- investigated (0.100 mmol dm-3). The precision of the technique was better than a relative standard deviation of 3.5% at the 0.5-mu-mol dm-3 leve land better than 2% at the 0.1 mmol dm-3 level, with a throughput of 30 samples h-1. Under optimum conditions, the detection limit was 0.1-mu-mol dm-3 (0.26 ng CN-). The effects of working potential, type of electrode coating, acidity of the reagent stream and interferents on the Fl signals were studied.