Details of requirements necessary for sample preparation
Powders used for XRF analysis must be very finely ground using either tungsten carbide or agate grinding apparatus. Powders that feel gritty are generally unsuitable for analysis, and such powders must be reground before being submitted for analysis. Normally at least 10g of powder should be available for major- and trace-element analysis.
Major-element concentrations are measured on 40mm-diameter fused glass discs. About 0.9g of sample powder is mixed with a borate flux using a 5:1 (flux:sample) dilution and fused in Pt-5%Au crucibles at 1100°C.
Please note the following important points:
- A 40mm-diameter glass disc cannot be made using less than 0.8g of powder.
- Samples containing sulphides or more than 100ppm of As, Sb, Pb or Sn must not be fused in Pt crucibles.
- Samples containing free carbon or organic material must be pre-ignited at 400°C in porcelain crucibles prior to fusion.
Trace-element concentrations are measured on pressed powder pellets. About 8g of powder is required to make a 40mm-diameter pellet but it is also possible to make 30mm-diameter pellets (using 4g of powder) and 13mm-diameter pellets (using 1g of powder) for some analytical applications. Gritty powders do not make stable pellets and the pellets will produce poor analyses.
Note: Pellets backed with pressed boric acid powder are not suitable for analysis in the current instrument.
This article was published on 25 Nov, 2016