Comparison between wet and dry oxidation methods of sample preparation for copper and zinc analysis of grassland herbage

Abstract

AbstractGrassland herbage samples with a range of copper (3–11 mg kg−1)) and zinc (10–53 mg kg−1) contents were analysed for Cu and Zn following sample solution preparation by four methods. An acid digestion procedure incorporating chloroform extraction and a second digestion step was compared with micro and macro digestion methods (both without solvent extraction) and a dry ashing method. The residues were dissolved in HCl and the metals determined by atomic absorption spectrophotometry.Results for Cu were much less variable than those for Zn. The dry ashing procedure gave higher analytical precision than did the acid digestion methods. However, when between‐plot field variation was included, the four methods gave similar coefficients of variation. Thus acid digestion, including the rapid micro method, appears to be suitable for routine analysis of herbage from field experiments. The double digestion procedure often gave low mean values for samples with high Cu and Zn contents, but it may be suitable for small numbers of samples with low Cu and Zn concentrations, while the higher precision of the dry ashing method may be useful for glasshouse or controlled environment studies with lower between‐plot variation.