Combining microwave and ultraviolet energy for sample preparation of polymer-based materials for further halogen determination

In this work, a microwave-assisted ultraviolet wet digestion (MAWD-UV) protocol was used to digest polymer-based materials (e-waste, food packing, medical-care materials, and individual protection equipment) for further halogen determination. Digests were suitable for Cl, Br, and I determination by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectrometry (ICP-OES). Fluorine determination was performed with ion selective electrode (ISE). The power radiation and the digestion solution were evaluated. The accuracy was evaluated by comparing the results with those obtained after neutron activation analysis (NAA) for Cl and Br or using microwave-induced combustion (MIC) as sample preparation for F and I. Two certified reference materials (CRM) of low-density polyethylene (ERM EC680k and EC681k) were evaluated, and no differences were observed (t-test, 95% confidence level) between the results and the certified values. Quantitative recoveries for Cl, Br, and I were obtained using 200 mg of the sample using diluted acid solution (15 mL of 0.5 mol L⁻¹ HNO₃ plus 10.6 mol L⁻¹ of H₂O₂), with a 40 min radiation program (700 W, 25 min ramp). No statistical differences (ANOVA, 95% confidence level) were observed between the MAWD-UV and ICP-MS results and the reference values for Cl, Br, and I for several samples. However, results were lower than the reference values for fluorine, indicating that digestion efficiency was poor for this analyte, which was probably as an organic molecule (likely polytetrafluoroethylene). The limit of quantification (LOQ) was 0.216 mg g⁻¹ for Cl, 3.33 µg g⁻¹ for Br, and 0.036 µg g⁻¹ for I using ICP-MS. The main advantage of MAWD-UV is that it enables decomposing several polymer-based matrices using diluted acid without halogen losses. The developed method represents an important contribution to the digestion of these hard-to-digest matrices and in compliance with green analytical chemistry, thereby being an advance in sample preparation.