Effect of acid digestion method on cobalt determination in plant materials

Many analytical methods for trace element determination in plant materials require decomposition of the sample. Hence, the mineralization procedure is of great importance for obtaining correct results. In this paper, microwave-assisted decomposition methods of plants have been compared with the classical open wet digestion procedure. Nine plant certified reference materials were analyzed for Co. The results obtained by radiochemical neutron activation analysis (NAA), when different decomposition methods were applied, have been compared with results obtained by non-destructive instrumental NAA and with certified (or information) values. Problems associated with decomposition of plant materials are discussed. It has been shown that the classical open wet mineralization procedure may in the case of certain biological materials lead to negative systematic errors of up to 14%. Even much higher negative systematic errors were observed when the amount of HF in the mineralization procedure was too small. The proposed microwave-assisted digestion procedure leads to accurate results of analysis and can be recommended as a standard approach for plant materials.