Additive manufacturing of platinum group element (PGE) reference materials with a silica matrix

The microanalytical community has an outstanding need for platinum group element (PGE) reference materials, particularly for trace element analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). National Institute of Standards and Technology (NIST) glasses contain Rh, Pd, and Pt, but lack Ru, Os, and Ir. Synthesis of silicate PGE standards has proven difficult due the tendency of PGEs to form metallic nuggets.

Additive manufacturing methods were used to produce PGE standards with a silica matrix. Monodispersed submicron PGE-doped Stöber particles were used as feedstock materials for electrophoretic deposition (EPD). Two-cm-sized samples produced by EPD were subsequently densified by thermal processing. The homogeneity of PGEs was tested using LA-ICPMS and concentrations were measured by laser ablation and solution ICPMS.

The PGE concentrations ranged from 0.5 to 3 μg/g. The inhomogeneity was at the 3% RSD level for Ru, Rh, Ir, and Os throughout and 5% for Pt and Pd in the interior of the samples. Based on LA-ICPMS analyses, the interiors of the two samples have near identical concentrations in PGEs.

The samples fabricated in this study represent the most complete and homogeneous PGE standards produced with a silicate matrix. The ability to produce multiple samples with the same composition provides opportunities for validating methods, monitoring long-term reproducibility, and facilitating interlaboratory comparisons.