Sample Preparation Considerations for XRF

While general sample preparation approaches were covered in Chapter 1, as seen from the examples earlier, XRF sample preparation requires some thought as well as an understanding of the chemical and physical properties of the sample material. Samples must be representative of the material to be analyzed. They must fit the sample holder being used and completely cover the opening in the sample holder or be larger than the measurement spot size being used. 

Minerals in particular present challenges to grinding and achieving a uniform grain size due to the complex composition of mineral samples, a problem known as the mineralogical effect. 

The ultimate preparation is to remove the grains from the sample to enable accnrate and efficient analysis of mnltiple types of materials. The best approach is to mix the sample and salts 

Since the physics of X-ray emission is governed by the sample and not by the instrumentation, special care needs to be applied to the use of handheld and portable XRF in the direct analysis of field samples that have not been prepared. Especially for the low Z elanents, one needs to understand that these only emit from very close to the sample surface. The calibration of the analyzer must be tuned to the preparation or presentation of the sample. If not done correctly (or not done at all), the values obtained from the analyzer will be incorrect. 

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