Amperometric determination of cyanides at the low ppb level by automated preconcentration based on gas diffusion coupled to sequential injection analysis

A simple, sensitive method for determining free cyanides is described. The assay is based on automated gas diffusion of the analyte using sequential injection analysis (SIA) coupled to amperometric detection on a silver working electrode. The effects of varying several parameters affecting the analytical procedure (including the flow rates of the donor and acceptor streams, the concentrations of the reagents and the sample volumes) were studied. The validity and quality of the method were also assessed, by examining its linearity, limits of detection and quantitation, precision, selectivity to potentially interfering substances. Its sensitivity can be enhanced by applying a simple preconcentration step, following which limits of detection were found to be 0.05-0.12 μg L−1. Application of the proposed assay to the analysis of tap, mineral and table water samples spiked at concentrations ranging from 1 to 10 μg L−1 CN−, yielded satisfactory recoveries (88-112%).