Tape Monitoring of Cyanide in Water Coupled with Metalcyanide Decomposition by UV Irradiation and Gas-Liquid Separation

A sample solution was pumped at a flow rate of 3 ml min-1 to a transparent PTFE tube (3 × 2 mm, 170 cm length), which was wound around an UV lump (rod shape, 17 mmφ, 145 mm length, λ = 254 nm, 4 W). A metal cyano complex {potassium hexacyanoferrate(III) (0∼0.2 mgCN dm-3)} was converted to CN- by UV (254 nm) irradiation of a sample solution at an efficiency of 100% (1 mol to 6 mol of CN-). Zn(II) and Cu(II)cyano complexes were successfully converted to CN- by the UV irradiation. The CN- produced was determined as follows. The sample solution was pumped to the mixing joint, where sulfuric acid (0.05 M) was mixed at a rate of 2 ml min-1. A mixture containing hydrogen cyanide was fed into a gas-liquid separation tube (pore size, 1 μ microporous Teflon tube of 2 mm i.d., 3 mm o.d., 900 mm length). Hydrogen cyanide that evolved from the gas-liquid separation tube was purged by purified air (700 ml min-1) onto HCN monitoring tape. The efficiency {CN-->HCN(gas)} obtained by using the gas liquid separator was about 3%. When the monitoring tape was exposed to HCN gas, the tape became homogeneously colored. The degree of color intensity was proportional to the concentration of CN- in the sample solution. The relative standard deviation of the response to 0.1 mgCN- dm-3 was 2.1%. The method has detection limits of 0.02 mgCN dm-3 with a sampling time of 5 minutes. Standard addition method showed that this method could detect cyanide in a treated waste liquid of a chemical laboratory.