Determination of cobalt in feedingstuffs by solvent extraction and graphite furnace atomic-absorption spectrophotometry
A convenient and reliable procedure is described for the determination of cobalt in feedingstuffs such as grass and cereal. After decomposition of the organic material by wet ashing, cobalt is extracted into a 2-nitroso-1-naphthol solution in xylene and the resulting 2-nitroso-1-naphthol-cobalt complex is determined by graphite furnace atomic-absorption spectrophotometry using pyrolytically coated graphite tubes and maximum power heating. In order to minimise contamination and handling, decomposition and solvent extraction are carried out in the same test-tube. Copper, iron, manganese, nickel and zinc, present in concentrations above those in normal feedingstuffs, do not interfere. The amount of cobalt in feedingstuffs determined by the procedure is independent of the sample size and for an NBS rice sample a content close to that of the certified value is found. By using a standard additions method linear graphs, parallel to the calibration graphs obtained in xylene and water, are obtained for grass and barley analyses. Recoveries of cobalt added to grass and barley are approximately 100%. Detection limits are 2 ng g–1 for grass and 1 ng g–1 for cereals.