Development of Dy, Ho, Er, Tm, and Sc mono-element standard solution certified reference materials (GBW08680-08684)

Dy, Ho, Er, Tm, and Sc mono-element solution certified reference materials (CRMs) with the certified value of 983.3 μg g^-1 were developed with high-purity lanthanide oxides by using a novel purity characterization strategy. In the purity characterization process, complexometric titration was first employed to acquire the total metal ion concentration reacting with EDTA. Twenty-seven non-lanthanide impurities were measured by an external ICP-MS method with three multi-element calibration solution CRMs as calibrants. To avoid REO(H)⁺ interference from the main lanthanide matrix, two strategies namely LA-ICP-MS and MD-ICP-MS were optimized and used for the measurement of 15 rare earth impurities. The purity of lanthanide oxide material was obtained by subtracting the 42 impurities from the total metal ions reacting with EDTA. After purity characterization, the solution CRMs were prepared with a gravimetric method, and the CRM values were verified with corresponding NIST rare earth solution SRMs. It was shown that 15 units with duplicate analysis are enough to demonstrate the homogeneity of these candidate reference materials. The statistical results also showed no significant trends in stability tests for 24 months. The final uncertainties of the CRMs were evaluated by combining uncertainty contributions including the sample characterization and gravimetric preparation (u_char), between-bottle homogeneity (u_bb), and stability (u_s). The relative expanded uncertainties of the five CRMs are 0.5%. These CRMs are primarily intended for use in the measurement and calibration procedures of lanthanide analysis in environmental and geological areas. Most importantly, the purity characterization strategy of this study will provide a new idea for the certification of high-purity and mono-element solution reference materials.