Staged digestion protocol for trace element determination in honey by ICP-MS: mitigation of matrix effects

Abstract This study aimed to improve sample preparation for trace element determination in honey by inductively coupled plasma mass spectrometry (ICP-MS), addressing challenges related to high sugar content, incomplete digestion, residual carbon, and matrix-induced interferences. An open-vessel Kjeldahl digestion method and four closed-vessel microwave-assisted digestion (CVMD) methods were evaluated. The Kjeldahl method gave acceptable recoveries for seven elements but showed poor performance for Cr, Fe, Cu, and Zn because of incomplete oxidation and matrix-related interferences, limiting its suitability for comprehensive multi-element analysis in honey. Among the microwave methods, a staged digestion approach involving controlled pre-digestion at 70 °C with HNO₃, followed by microwave digestion using an HNO₃/H₂O₂ mixture, showed the best overall performance. Acceptable recoveries (85–115%) were obtained for most elements, including V, Mn, Co, Ni, Zn, As, Cd, and Pb, whereas Cr showed over-recovery (161.2%), likely because of residual spectral interference. Precision was acceptable for several elements, although greater variability remained for Mn, Ni, and Pb. Significant differences among digestion methods were observed for most elements. Overall, the proposed approach improved matrix decomposition and reduced interferences, although further validation using different honey types is still needed.