Determination of sub-microgram amounts of cobalt in plants and animal tissues by extraction and atomic-absorption spectroscopy

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Abstract
Atomic-absorption spectroscopy is used to determine cobalt in plants and animal tissues after solvent extraction of the 1-nitroso-2-naphthol complex from an acidic solution of the sample. The solvent is evaporated and the complex is dissolved in ethyl methyl ketone for aspiration. The method is more sensitive than, and as accurate and precise as, a colorimetric procedure involving nitroso-R salt, and is much less tedious. Cobalt can be determined in the range 0·05 to 1 µg in the final 1-ml sample solution (corresponding to 0·05 to 1 p.p.m.). With a 5-g sample from 0·01 to 0·2 p.p.m. of cobalt in samples (dry matter) can be determined. The method can, therefore, be applied readily to pasture samples containing 0·1 p.p.m. of cobalt and less, levels that are considered likely to cause deficiency in ruminants. At 0·07 p.p.m. of cobalt the coefficient of variation is 14 per cent. At higher concentrations (0·14 p.p.m.) of cobalt in pasture and liver samples the coefficients of variation are 11 and 6 per cent., respectively.

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