WET DIGESTION OF VEGETABLE TISSUE USING A DOMESTIC MICROWAVE-OVEN

A rapid, accurate, precise and inexpensive method for the wet digestion of vegetable materials is proposed. A conventional microwave oven was used as the energy source. Total phosphorus, calcium, magnesium, potassium and sulphur were determined by inductively coupled plasma atomic emission spectrometric techniques. A varied assortment of plants (algae, seagrasses, freshwater plants and terrestrial plants) and plant parts (leaves, wood, rhizomes, roots and bark) were digested to test the inter- and intra-assay method precision and the effects of the characteristics of the material on its efficiency. Three standards (NBS SRM Pine Needles and Citrus Leaves and the intercalibration sample from the Forest Research Institute of New Zealand Pinus radiata leaves) were also digested to test the accuracy of the method. All samples were totally digested after 20 min or less. The values found for standards coincided in all instances with the certified values. The average recovery was 97.2% and ranged from 81.3% to 114.5%. The variability of the method, in terms of the standard deviation of the mean, varied from 3.0% (Ca) to 9.72% (K). Practical considerations such as instrument availability and purchase price, operating costs, acid volume needed and especially the number of samples processed per hour were compared between the present method and classical methods using conventional heaters. Safety aspects are considered.