SPECTROPHOTOMETRIC DETERMINATION OF METALS WITH SUITABLE CHELATING AGENTS IN MICELLAR MEDIA

Abstract

The aim of present study is to develop simpler high sensitive, selective, and rapid direct spectrophotometric methods to the determination of trace metal ions. The method is based on the metal complex formation with chelating agents. The insoluble metal complexes were extracted in organic solvent then were determined spectrophotometrically for the determination of metal ions. Developed methods do not require tedious solvent-extraction steps; hence the use of carcinogenic carbon tetrachloride or chloroform is replaced by the micellar method. Proposed methods are more selective, non-extractive, simple and rapid than all existing spectrophotometric methods. In the field of metal ion complexation, the ability of micellar system to solubilize insoluble metal-complex has been investigated to enhance the analytical merits of proposed method. Use of surfactants showed increase in the molar absorptivity and bathochromic shifts in the wavelength of maximum absorbance. In the present study rapid and sensitive methods have been developed by using chromogenic complexing reagents in anionic sodium dodecyl sulphate (SDS) and cationic cetyltrimethylammoniumbromide (CTAB) surfactants by improving the sensitivity, selectivity, detection limits, Beer’s law range, cause a change in the pH, red-shifts in the absorption bands and reducing the interferences of the analytes by using normal mode and first derivative mode spectroscopy. The present research is continuation and extension work of G.A. Shar Ph.D thesis 2003, By exploring in various surfactants and development of methods by optimizing various parameters. Metal ions studied are: cobalt (II), iron(II), nickel (II), copper (II) and cadmium (II). The chelating agents used were 1-(2-pyridylazo)-2-naphthol (PAN), ammonium pyrollidinedithiocarbamate (APDC) and 1-nitroso-2-naphthol (NNPh). The characterizations of metal complexes were investigated by infrared IR spectroscopy. Different experimental conditions were optimized the include pH, amount of the complexing reagent and the stability of the metal complex. The interfering effects were studied and interferences were lowered by adjusting the pH/ the masking agents and by the use of first derivative mode spectroscopy. The detection limits for these metal ions were obtained up to 1.7 ngmL-1 in first derivative mode spectroscopy. The use of derivate mode spectroscopy has removed the interferences of the analytes and lowered the detection limit upto trace ng level which showed improved sensitivity and selectivity of the methods than reported normal mode spectroscopy. The results of the metal ions determination were compared with official methods and showed good agreement in both methods. No significant difference was found between two methods by applying t-test. The precision and accuracy of measurements have been evaluated using elemental comparator standards and certified reference materials, respectively. The methods have been applied to the determination of the metal ions in biological, pharmaceutical and environmental samples.