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 0.12 M 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 0.08 M 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.