Determination of Trace Cyanide in Water by Isonicotinic Acid-Barbituric Acid Spectrophotometry Based on Air Separation and Enrichment

In view of the conversion of cyanide to cyanogen chloride is an independent intermediate step for the determination of cyanide by isonicotinic acid-barbituric acid spectrophotometry in HJ 484-2009, using the characteristics of low boiling point (14 ℃) and good stability of cyanogen chloride, a method for the determination of trace cyanide in water by isonicotinic acid-barbituric acid spectrophotometry based on air separation and enrichment was proposed. Using air as carrier gas and the solution with the mass concentration of isonicotinic acid of 17.20 g·L^-1 and barbituric acid of 8.40 g·L^-1 as absorption solution(pH 5.85), the specific separation and enrichment device was used for accomplishment a series of processes, including air purification, the conversion of cyanide to cyanogen chloride, the separation of cyanogen chloride, and the absorption of cyanogen chloride and conversion to polymethin dye, and the absorbance of absorption solution at 600 nm was measured by spectrophotometer. It was shown that the conversion coefficient of cyanide was 94.2%, and the enrichment factor was 11.3, with detection limit (3s/k) of 0.1 μg·L^-1 and linear range of determination was 0.4-28.3 μg·L^-1 when the volumes of the sample and absorption solution were 60.0 mL and 5.00 mL, respectively, and the flow rate of air was 0.10 L·min^-1 by using three-stage absorption and total absorbance as response value. The method was applied to determination of trace cyanide in well water and river water, in which the mass concentration of cyanide was in the range of 1.2-8.9 μg·L^-1, and the recoveries were in the range of 92.9%-104%.