MICROWAVE DIGESTION OF FERTILIZERS AND SOIL AMENDMENTS

The trace element pollution hazard of the continuous and large scale a pplication of fertilizers and other amendments to soils depends in par t on the chemical composition of these materials. Complete sample diss olution is generally required prior to total elemental analyses. The o bjectives of this study were to evaluate closed vessel microwave diges tion procedures, using HNO3, HF, H2O2, and H3BO3, for the total dissol ution of fertilizers and soil amendments and to develop a general dige stion guide for individual samples. Twenty-six materials, including co mmercial fertilizers, rock phosphate, liming materials, organic source s, and a soil sample were studied. More than 99.5% of each of these ma terials could be dissolved. Commercial nitrogen (N) fertilizers, most of the ammonium phosphates, and a potassium chloride sample could be c ompletely dissolved using exclusively HNO3. The other samples required HNO3 and HF, used either in mixtures or consecutively in a stepwise p rocedure. The sewage sludge materials, the soil sample, and one of the rock phosphates were the only samples that could not be totally disso lved. No improvement in the digestions was observed by including H2O2. No significant contamination was evident during the digestions and sa tisfactory recoveries of 14 trace elements were obtained in digests of 2 standard reference materials. The proposed dissolution procedures a re simple and safe. The usual quickness of microwave procedures was pa rtially sacrificed to obtain a more complete dissolution of the sample s. Digests obtained with these procedures could be potentially analyze d for other analytes, with the obvious exceptions of N, fluorine (F), and boron (B).