A method for free and strongly complexed cyanide measurement in river water was developed. Recovery tests from solution with and without river water, using various solvent combinations and background control were investigated to obtain an accurate and precise extraction method for the measurement of hydrogen cyanide in Kaduna River, Nigeria. The method enhanced the determination of undissociated hydrogen cyanide and the equilibria between hydrogen cyanide, cyanide ion and complex cyanides. A small portion of the hydrogen cyanide was extracted by equilibrating the sample with methylchloroform (1,1,1-trichloroethane), methanol, hexane and 2-octanol inclusions, respectively, in the solvent matrix with 2.5 M NaOH. The extracted hydrogen cyanide is transferred into tetrasodium pyrophosphate solution and determined colorimetrically. A total cyanide concentration of 0.03 mg/L in the river water and 0.40 mg/L in an effluent water sample, respectively, were obtained by the proposed method compared to 0.020 and 0.45 mg/L from the established diffusion method. The proposed method was sensitive and reproducible in the range of 0 to 5 mgL-1 of hydrogen cyanide with detectable limit of about 0.01 mgL-1.
KEY WORDS: Solvent extraction; Free hydrogen cyanide; River water
Bull. Chem. Soc. Ethiop. 2007, 21(3), 305-313.