Determination of cyanide ion with gas-liquid separation tube and monitoring tape

Abstract

A sample solution was pumped at a flow rate of 3 ml min−1 to the mixing joint, where a 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 μm; microporous Teflon tube of 2 mm i.d., 3 mm o.d., 900 mm length). Hydrogen cyanide evolved from the gas-liquid separation tube was purged by purified air (400 ml min−1) onto HCN monitoring tape. The efficiency of the gas-liquid separator used was about 3%. The monitoring tape used was porous cellulose tape containing silica gel, N,N-diethyl-p-phenylenediamine, Cu(CH3COO)2 and glycerin. When the tape was exposed to HCN gas, the tape became colored homogeneously. 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 1.2%. The calibration curve showed a rectilinear behavior in the range of 0.01∼0.3 mgCN dm−3. The method has detection limits of 0.01 mgCN dm−3 for free cyanide ion with a sampling time of 5 min. This method could detect free cyanide ions, and indirectly Cu(II) and Cd(II) cyano complexes when the metal concentrations were below 10 mg dm−3.