Abstract
Environmental Protection Agencies impose stringent limits for weak-acid dissociable metal-cyanide complexes (WAD) content in waters. The maximum contaminant level in drinking water is as low as 50 µg/L as CN-. Hence, sensitive methods for WAD cyanide determination are strongly required. Recently, ninhydrin reaction with free cyanide has been proven as a very sensitive at 485 nm (e = 1.2 105 L/mol.cm), fast (15 min), selective and with non-toxic reagents. In the presence of free cyanide the absorbance measurement was based on the formation of a red hydrindatin resulting from cyanide’s catalytic effect on ninhydrin at pH 10.8. This report presents the results from a study on the reaction between ninhydrin and complexed cyanide at ambient conditions. The WAD complexes: Hg(CN)42-; Ni(CN)42-; Cu(CN)43-; Ag(CN)2-; Zn(CN)42-; Cd(CN)42- are discussed. The reaction kinetic and standard curves are presented. Ligand exchange approach was applied without additional separation. Ninhydrin was showed to be selective and sensitive for direct cyanide quantification.
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