Spectrophotometric determination of cyanide ion in waste water using copper(II) and N,N-diethyl-p-phenylenediamine

Abstract

Spectrophotometric determination of cyanide ions in water was studied using Cu(II) ions and N,N-diethyl-p-phenylenediamine(DPD). A cyanide ions reacted with Cu(I) ions, producing a stable complex, CuCN (s.p.=3.5×10−20). Then, Cu(II) ions were reduced to Cu(I) ions with DPD owing to a decrease of Cu(I) ions. The concentaration of the coloring oxidant of DPD was proportional to the concentration of cyanide ions between 0.1 and 2.0 mg CN− l−1. The coloring development by this method was attained in one minute. A copper formate was the most suitable copper salt for a reaction in copper chloride, copper sulfate and copper acetate because of its highest sensitivity and lowest blank. The influences of co-existing metal ions [(Cr(III): 40 mg l−1), (Ag(I): 0.3 mg l−1), (Fe(II): 0.4 mg l−1), (Fe(III): 3 mg l−1), (Ni(II): 0.16 mg l−1), (Co(II): 0.01 mg l−1) and (Zn(II): 100 mg l−1)] were less than 10% for 0.4 mg l−1 of cyanide ions. No influences of co-existing metals on the linearity of calibration curve were observed. This method is very simple, and can be used for the pre-detection of cyanide ions in waste water.