Complexometric determination of copper in isolation, alloys and complexes using DL-cysteine as a selective masking agent

Abstract

An accurate, selective and rapid complexotitrimetric method is described for the determination of Cu^II in the presence of other metal ions. The method is based on the selective complexing ability of cysteine with Cu^II. Copper in the aliquot is initially complexed by the addition of ethylenediaminetetraacetic acid (H₄edta) solution and the excess H₄edta is titrated against Pb(NO₃)₂ solution (pH 5.0–6.0) using hexamine and Xylenol Orange. A known excess of DL-cysteine in water is then added to release the H₄edta from the Cu^II—H₄edta complex. This is subsequently titrated against Pb(NO₃)₂ to the same sharp end-point. The amount of H₄edta released from the complex is thus equivalent to the amount of Cu^II in the solution. The method works well for Cu in various alloys and metal complexes. Reproducible and accurate results are obtained in the concentration range 3–32 mg per aliquot with a relative error of <0.6% and a standard deviation of <0.04%. The effect of various cations and anions is also studied. The interference of a number of ions, such as Zr^IV, Sn^IV, TI^III, Hg^II and Pd^II can be overcome by the use of suitable secondary masking agents.