SIMULTANEOUS DETERMINATION OF COBALT AND NICKEL IN STANDARD ALLOYS, ENVIRONMENTAL AND BIOLOGICAL SAMPLES BY DIFFERENTIAL-PULSE POLAROGRAPHYAFTER PRECONCENTRATION OF THEIR MORPHOLINE-4-CARBODITHIOATES ON MICROCRYSTALLINE NAPHTHALENE OR MORPHOLINE-4-DITHIOCARBAMATE-CTMAB-NAPHTHALENE ADSORBENT

A highly sensitive, selective, simple and economical differential puls e polarographic (DPP) method has been developed for the simultaneous d etermination of trace amounts of cobalt and nickel in standard alloys, biological and environmental samples. The morpholine-4-carbodithioate s 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 dete rmined simultaneously with DPP after desorption with 10 mi of 1 M HCl. These metals can alternatively be adsorbed on orpholine-4-dithiocarba mate-cetyltrimethylammonium bromite-naphthalene (MCDT-CTMAB-naphthalen e) adsorbent packed in a column and determined similarly. The detectio n limits are 0.15 ppm for cobalt and 0.20 ppm for nickel at minimum in strumental settings (signal-to-noise ratio=2). The linearity is mainta ined 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/c olumn methods respectively. Various parameters such as the effect of p H, volume of aqueous phase and interference of a large number of ions on the estimation of these metals have been studied in detail to optim ize the conditions for their simultaneous estimation in various comple x materials.