Synthesis of micro-analytical standards

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SEM image of particles grown in a solution doped with platinum group element at the ppm level.

In-situ chemical and isotopic analyses can suffer from matrix effects – analytical artifacts created by using a calibration standard with a different composition to the sample. Best practice is therefore to employ standards with a matrix composition that closely matches that of the sample. Synthetic standards for in-situ analyses are often made by melting mixtures of the required starting materials for an extended period of time, in order to aid homogenization, followed by rapid quenching to form a glass. However, for platinum-group-elements (PGE) in a silicate matrix, this procedure induces formation of metallic nuggets, making the quenched samples heterogeneous and unsuitable for use as calibration standards. As a result, there is a pressing need for novel methods that produce homogeneous PGE micro-analytical standards with a silicate matrix.

Working with Dr. Tashi Parsons-Davis, we used a modified Stöber reaction to grow micron-sized particles from a solution doped with PGE. These PGE-doped particles were formed into appropriately sized blocks using additive manufacturing techniques. Upon calcining, the matrix of these particles is SiO2. Subsequently, the samples are sintered to yield a coherent sample for use as micro-analytical standards. To suppress the formation of metallic nuggets, sintering is performed below the melting temperature of the sample, at controlled atmospheric conditions, and for shortest duration possible. Laser ablation inductively coupled mass spectrometry (LA-ICPMS) analyses confirm the homogeneity of PGE in these samples. The same method can be used to synthesize standards for other elements, and the amount of synthesized material is only limited by the size of the container used for the Stöber reaction. This method therefore allows production of standards in quantities large enough for widespread distribution.

Reference:

  1. Sio, C. K., Parsons‐Davis, T., Lee, E., Wimpenny, J., Pascall, A. J., Kuntz, J. D., Goodell, J. J., Roberts, K. E., Bandong, B. B. & Bennett, N. R. (2020). Additive manufacturing of platinum group element (PGE) reference materials with a silica matrix. Rapid Communications in Mass Spectrometry, 34(7), e8627.