Combining Ultrasound-Assisted Extraction and ICP-MS for As, Cd, Cr, and Pb Determination in Atmospheric Particulate Matter

A simple, fast, and efficient ultrasound-assisted extraction (UAE) method for As, Cd, Cr, and Pb determination in atmospheric particulate matter (PM) by inductively coupled plasma mass spectrometry (ICP-MS) was developed. For the extraction procedure, the samples and the extraction solution were added directly into polypropylene vessels and placed in the ultrasound (US) bath. The following parameters were evaluated: i) sample mass: 50 to 500 mg, ii) extraction solutions: HNO3, HCl, and HF, and iii) extraction time in the US bath: 10 to 30 min (80 °C). Accuracy was evaluated using certified reference materials (CRMs) of river sediment, (BCR 320, NIST 2704, and 8704) and by comparison with values obtained by using the method recommended by the United States Environmental Protection Agency (EPA 3052). The agreement with the CRMs and with the official method were better than 95% for all analytes when 100 mg of sample, 5 mL of an extraction solution containing 4.75 mL of 3:1 HNO3:HCl (50%) + 0.25 mL of HF, and 20 min of heating (80 ºC) were used. Analytes were also determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and no statistical difference was observed (t-test, 95% confidence level) compared to ICP-MS results. The analyte concentration in the PM samples ranged from 6.60 ± 0.41 to 17.9 ± 0.9 µg g-1 for As, from 0.839 ± 0.049 to 11.8 ± 0.6 µg g-1 for Cd, from 31.3 ± 2.1 to 59.6 ± 3.5 µg g-1 for Cr, and from 13.5 ± 0.5 to 123 ± 6 µg g-1 for Pb. Low limits of detection (LODs) of 0.90, 0.015, 0.640, and 0.085 µg g-1 were obtained for As, Cd, Cr, and Pb, respectively, which are important for the determination at low concentrations. Finally, the proposed method combined important advantages such as the use of a relatively low-cost sample preparation system (UAE method) with low reagent consumption, and a low volume of laboratory residues.