Influence of chemical and mineralogical properties of organic amendments on the selection of an adequate analytical procedure for trace elements determination

Six digestion procedures were tested to improve extraction methods for determination of trace elements in various organic amendments with high inorganic fractions. These procedures were tested in terms of pH, CaCO3, organic matter, elemental analysis, BCR sequential extraction and X-ray diffraction analysis. Aqua regia extraction (ISO 11466), total digestion HF–HNO3–HClO4 and four microwave-assisted digestions (i.e., HNO3, HCl–HNO3, HNO3–HF and HCl–HNO3–HF) were used. The effect of acid mixtures on microwave-assisted digestion of mineral fractions was assessed by Si and Al analysis and X-ray diffraction in the solid residues obtained. Microwave HF acid mixtures obtained highest trace element recoveries for all tested metals except Al. CaF2 and CaAlF5 precipitates were also detected using X-ray diffraction in the residues after microwave digestions with HF acid mixtures of amendments with high calcium content. A decision flowchart was suggested to determine the best acid mixture according to the amendment and the metals to be analyzed.