Comparative study on open system digestion vs. microwave-assisted digestion methods for trace element analysis in agricultural soils

The aim of this work was to evaluate two different digestion procedures for the determination of the concentration of trace and major elements (As, Cd, Co, Cu, Cr, Fe, Mg, Mn, Ni, P, Pb, Sb, V, Zn) in five hundred randomly selected soil samples from LUCAS Soil Survey. The two procedures employed in sample preparation are the open vessel digestion, which is described in the ISO 11466:1995 [1], and the microwave assisted digestion, implemented in the prEN16174 document [2]. Certified Reference Materials (NIST 2711 and BCR 141R) were also analysed using both pre-treatment approaches in order to determine sample recoveries and assess quality assurance and quality control (QA/QC) of the methods. Results obtained with samples and CRMs analysis are useful to compare the two tested digestion procedures for recovery rate, safety, cost and time taken. The results obtained from reference materials and soil samples revealed a good agreement between both procedures and the certified values. T-test was also employed to evaluate the hypothesis of equal mean between concentration determined after the open vessel and microwave-assisted digestions. This test demonstrates that, for the majority of the elements, the hypothesis is verified. The microwave procedure was then recommended as the method for the digestion of the 22 000 soil samples of the LUCAS Soil Survey, based on good precision and accuracy, speed and safety.