Simultaneous Determination of Pb(II), Cu(II) and Ni(II) with MEDTA by Ultraviolet and Visible Derivative Spectrophotometry

Abstract

Aims: Since the end of the nineteenth century, when Werner proposed his theory of co-ordination, the study of metallic compounds has continued to attract the interest of researchers. The present work had as its aim to achieve simultaneous determination of Pb(II), Cu(II) and Ni(II) by means of UV-VIS and derivative spectrophotometry, using methyl-ethylene-diamine-tetraacetic acid, MEDTA, as a chelating agent. Study Design: The visible and ultraviolet spectroscopy allows both to identify a chemical substance (qualitative analysis) and to determine its concentration (quantitative analysis). In the work, the UV-VIS and derivative spectrophotometry is used for the determination simultaneous of Pb(II), Cu (II) and Ni (II). The method proposed uses methyl-ethylene-diamine-tetracetic acid (MEDTA) as a chelating agent and absorption spectrophotometry for quantification. Place and Duration of Study: The study is part of a doctoral thesis, was conducted in the Analytical Chemistry Department of the University of A Coruña. Methodology and Results: In the range of wavelengths between 200 nm and 500 nm, the complexes formed by MEDTA with Pb(II) or Cu(II) present a single absorption peak at 256 nm and 272 nm respectively, whilst the complex formed with Ni(II) presents two peaks at 250 nm and 380 nm. In the samples in which the three elements are present, the spectrum shows two peaks: the first at 260 nm, due to the superposition of the individual absorption peaks of the cations at 250, 256 and 272 nm and the second at 380 nm, characteristic of Ni (II). It is necessary the joint use of the normal or direct spectrum (zero order) and the first derivative thereof by means of the zero-crossing-point method for its simultaneous determination. In the development of this method the influences exercised by pH, time and temperature were determined. The reproducibility of the method proposed was checked, as was the interference from certain of the more frequent anions and cations that might affect the determination. Conclusion: As long as the optimum conditions indicated are maintained, the method of analysis proposed makes possible the simultaneous determination of Pb(II), Cu(II) and Ni(II) using MEDTA as a chelating agent and UV-VIS and derived spectrophotometry. Then method was successfully tested through the use of blind samples.