Simultaneous Determination of Cobalt and Nickel in Standard Alloys, Environmental and Biological Samples by Differential Pulse Polarography After Preconcentration of Their Morpholine-4-carbodithioates on Microcrystalline Naphthalene or Morpholine-4-dithiocarbamate-CTMAB-naphthalene Adsorbent

Abstract

A highly sensitive, selective, simple and economical differential pulse polarographic (DPP) method has been developed for the simultaneous determination of trace amounts of cobalt and nickel in standard alloys, biological and environmental samples. The morpholine-4-carbodithioates of cobalt and nickel are quantitatively adsorbed on microcrystalline naphthalene in the pH range 3.5–9.0 and 4.1–9.5 respectively and determined simultaneously with DPP after desorption with 10 ml of 1 M HCl. These metals can alternatively be adsorbed on morpholine-4-dithiocarbamate-cetyltrimethylammonium bromide-naphthalene (MCDT-CTMAB-naphthalene) adsorbent packed in a column and determined similarly. The detection limits are 0.15 ppm for cobalt and 0.20 ppm for nickel at minimum instrumental settings (signal-to-noise ratio=2). The linearity is maintained in the concentration ranges, cobalt 0.6–12.0/0.6–7.0 and nickel 1.0–20.0/1.0–12.0 ppm with a correlation factor of 0.9996 and relative standard deviations of 1.2 and 1.4% for microcrystalline naphthalene/column methods respectively. Various parameters such as the effect of pH, volume of aqueous phase and interference of a large number of ions on the estimation of these metals have been studied in detail to optimize the conditions for their simultaneous estimation in various complex materials.