Accuracy evaluation of ultrasound probe sonication and microwave-assisted extraction systems for rapid single extraction of metals in soils

Abstract

Ultrasonic probe sonication (UPS) and microwave-assisted extraction (MAE) have been evaluated as alternatives to the conventional Standards, Measurements and Testing program (SM&T) procedures for single extraction of metals in soils, in order to reduce the extraction time and the consumption of samples and extracting agents. Optimization studies were carried out on the certified reference materials (CRMs) BCR 483 (sewage sludge amended soil) and BCR 700 (organic rich soil) for accuracy evaluation of the proposed methods. Extractable concentrations of Cd, Cr, Cu, Ni, Pb and Zn using 0.01 mol L⁻¹ calcium chloride (CaCl₂) (in BCR 483), 0.43 mol L⁻¹ acetic acid (CH₃COOH) and 0.05 mol L⁻¹ ethylenediaminetetraacetic acid (EDTA) at pH 7.0 (in both CRMs) were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The extraction time for the CaCl₂ extraction method was reduced from 3 h (conventional procedure) to 2 min by UPS or 5 min at 50 °C by MAE. Similarly, the time required for acetic acid extraction was also reduced from 16 h to 15 min by UPS or 15 min at 120 °C by MAE. Finally, the extraction time with EDTA was reduced from 1 h (conventional procedure) to 2 min by UPS or 5 min at 50 °C by MAE. For these extraction conditions proposed, quantitative extraction recoveries were obtained for most elements studied. In addition, the amount of sample and extractants was drastically reduced, maintaining the sample weight/extractant volume ratio.