Optimization and validation test of a sonoreactor-assisted methodology for fast and miniaturized extraction of trace elements from soils.

ABSTRACT

We have proven the overall applicability of the novel sonoreactor VialTweeter as a tool for a fast, miniaturized and economical extraction of trace elements, namely Cu, Zn, As, Cd, Pb, from soil samples, followed by ICP-MS. The proposed analytical approach applicable in the context of environmental monitoring of elemental soil pollutants, since the selected analytes are relevant pollutants whose presence in soils produces significant effects on their quality affecting animals, plants and humans. The optimum conditions for the extraction of trace metals assisted by the sonoreactor, selected by a Box-Behnken (BBD) experiment design along combined with a response surface methodology were 93% sonication amplitude, 450 s sonication time, 80% HNO3 and a solvent/sample ratio of 0.18 mL/mg. The proposed sonoreactor-assisted extraction methodology provides several advantages of respect to the standard acid digestion taken as comparison term for validation, including a shorter pretreatment time and use of less sample and reagents amounts. However, mixed validation results against the standard acid digestion (taken as a model providing accurate results) were obtained depending on the analyte, with the best results in the case of cadmium that could be measured after US extraction without systematic error respect to the standard acid digestion. Copper and lead can be determined by the proposed US extraction plus ICP-MS only after applying a correction factor based on the slope of the correlation with the standard acid digestion. US treatment for As determination can be only useable by applying a constant correction factor based on the intercept of the correlation line, whereas Zn determination requires a correction based both in the slope and intercept of the correlation line.