Evaluating LA-ICP-MS and digestion-based ICP-MS methods for trace elements determination in oil shale and its solid...

The complex matrix of oil shale and its solid wastes poses significant challenges for trace element quantification. This study compares the performance and challenges of seven analytical methods for quantifying 19 trace elements (V, Cr, Mn, Co, Ni, Cu, Zn, As, Zr, Mo, Sn, Sb, Ba, La, Ce, Pb, Bi, Th, and U) in oil shale and its solid wastes. These methods include matrix-matched and matrix-independent laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method employing different internal standards, as well as traditional solution-based inductively coupled plasma mass spectrometry (ICP-MS) with three digestion protocols (HNO₃, HNO₃-HF, and HNO₃-HCl-HF-HClO₄). Validation with certified reference materials (SGR-1b, ACIRS-A1-2016) and practical samples (oil shale and related residues from laboratory and power plant combustion) showed that matrix-matched LA-ICP-MS using lithium borate glass standard effectively mitigated matrix effects and achieved superior analytical performance (recoveries within ±15% with coefficient of variation (CV) ≤ 5%) and |En| < 1 for 5/9 elements in ash matrices) compared to matrix-independent LA-ICP-MS and ICP-MS methods. While conventional ICP-MS methods performed well for certain elements (e.g., Ba, Mn, and Cr), but showed limited accuracy and consistency for others due to remaining matrix effects, even with internal standard correction, especially in complex ash matrices. These findings underscore the strengths and limitations of each technique and highlight the potential of matrix-matched LA-ICP-MS as a promising tool for rapid and accurate trace element quantification, offering promising applications in resource recovery and environmental risk assessment in the oil shale industry.