Development of a multi-element quantification method for technical polymers containing refractory oxides after microwave-assisted digestion using HBF4

Polymers used in packaging, medical devices, and construction often contain inorganic additives, including stabilizers, fillers, pigments, and antioxidants. Quantitative elemental analysis of these additives is essential for quality control, regulatory compliance, recycling, and the assessment of microplastics, but is complicated by refractory oxides (e.g., TiO2, Al2O3, ZrO2) that are difficult to dissolve quantitatively. This study presents a two-step, microwave-assisted digestion method using tetrafluoroboric acid (HBF4) for comprehensive elemental analysis of technical polymers containing such oxides. In the first step, the polymer matrix is oxidized using HNO3 and H2O2 at 200 °C; and in the second step, HBF4 is added and digestion continues at 180 °C to dissolve refractory oxides while avoiding the use of free HF. Method development was performed on polyethylene containing various oxides, and on polyvinyl chloride containing metal soaps, CaCO3, and TiO2. The protocol was benchmarked against HF-based digestions. The optimized conditions (4 mL HNO3 + 1 mL H2O2, 75 min at 200 °C; 1 mL HBF4, 45 min at 180 °C) gave recoveries typically between 90 and 105% for Al, Ca, Mg, Ti, and Zr with relative standard deviations ≤5% for most analytes. Limits of detection by inductively coupled plasma mass spectrometry (ICP-MS) were ≤2.6 mg kg-1 (LOQs ≤8.5 mg kg-1) for most elements. Accuracy and applicability were confirmed for the polymer certified reference material ERM®-EC681k and for polycarbonate and acrylonitrile-butadiene-styrene masterbatches containing refractory oxides, demonstrating a robust, broadly applicable, and HF-free sample preparation strategy for elemental analysis of technical polymers and microplastics.