Preconcentration of nickel and cobalt on algae and determination by slurry graphite-furnace atomic-absorption spectrometry

Unicellular green algae have been utilized to preconcentrate Ni(2+) and Co(2+) ions from sea-water and riverine water samples. Studies have shown that rinsing the algae with 0.12M hydrochloric acid improves the adsorption of nickel and cobalt, and the optimum range of pH of extraction is wide. The maximum extraction efficiencies were 84 and 73% for Ni and Co, respectively, at ng/ml levels. The sea-water matrix and relatively small amounts of many impurities reduce the adsorption efficiency for both nickel and cobalt. The preconcentration is achieved by mixing 6 mg of algae with 50-100 ml of sample, and subsequently isolating the algae by centrifugation. The pellet of algae is then resuspended in 1 ml of 0.08M nitric acid, and analyzed as a slurry by graphite-furnace atomic-absorption spectrometry. The values found for nickel and cobalt in riverine (SLRS-1) and sea-water (CASS-1) standard reference materials are within the limits of certification.