On-line determination of cyanide in the presence of sulfide by flow injection with pervaporation

A pervaporation-flow injection (PFI) method is described for the analysis of cyanide in the presence of sulfide. The interfering sulfide ion in the injected sample is precipitated on-line using an acidified lead nitrate reagent solution before the donor stream enters the pervaporation cell. Using amperometric detection at a silver electrode set at ?50 mV (vs Ag/AgCl), linear calibration was obtained in the range 0.02–100.0 mg l^?1 with a detection limit of 1.0 μg l^?1. Sample throughput was of the order of 12–15 h^?1. When the method was applied to the analysis of synthetic samples, there was no significant interference from sulfide at concentrations up to 50 mg l^?1. Thiocyanate did not interfere at levels up to 1000 mg l^?1. When applied to industrial samples containing sulfide and thiocyanate ions where the cyanide ions are predominantly complexed with various metal ions the PFI method was found to give results close to those obtained by standard distillation methods for weak acid dissociable (WAD) cyanide.