Continuous Determination of Cyanide in Waste Water with Ion Selective Electrode and Gas-Liquid Separation

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Abstract
The waste water sample is pumped at the flow rate of 4cm3 min-1 to the mixing joint, where a reaction solution (5×10-3M bismuth nitrate-containing sodium acetate buffer at pH 5.0) is mixed at the rate of 1cm3 min-1. Then the mixture containing hydrogen cyanide is fed into a gas-liquid separator. The hydrogen cyanide permeates through a Teflon membrane (0.80μm pore size, 0.08mm thick) into an absorption solution (0.02% sodium hydroxide) flowing at 24cm-3 h-1. The cyanide ion produced is measured with the cyanide selective electrode. The response time is about 1.3min at a concentration of 1×10-4M cyanide. The Nernst equation is valid with a relative standard deviation of less than 2.8% in the range between 1×10-3 and 1×10-6M. The lower detection limit is 1×10-7M (2.6 CN- ppb). This method can detect free cyanide ion and indirectly metal cyano complexes whose stability constants are below 1017.