Direct determination of rare earth elements in atmospheric precipitation using a membrane desolvation ICP-MS/MS with N ₂ O as the reaction gas

Analyzing rare earth elements (REEs) in atmospheric precipitation can reveal their sources and migration patterns. However, their direct determination in atmospheric precipitation using ICP-MS/MS remains challenging owing to low (sub-ng L^-1) levels and mass spectral interference. This study established a reliable ICP-MS/MS method using a membrane desolvation system to enhance the sensitivity of REEs detections and employing N₂O as the reaction gas to eliminate spectral interference for the direct measurement of REEs in atmospheric precipitation. The production rates of REE monoxides were significantly enhanced when using N₂O as the reaction gas instead of O₂. In particular, the yield of EuO⁺ increased to 64.9%, while that of YbO⁺ increased to 39.5%. A regular 10% signal suppression of REE⁺ was observed in the presence of matrix using membrane desolvation and employing ¹⁸⁵Re as an internal standard effectively improved the results by >98%. The instrumental detection limits of the proposed method ranged from 0.001 ng L^-1 for Lu to 0.022 ng L^-1 for Nd. The results for REEs in the certified reference material (SLRS-6) at a 1 : 10 dilution was consistent with the values reported in the literature. Thus, the proposed method was employed to analyze atmospheric precipitation samples. The accuracy of the results demonstrated that this method has the potential for routinely measuring sub ng L^-1 levels of REEs in freshwater samples, offering advantages regarding sample throughput and reduced handling.