Which sample types are typically suitable for XRF analysis?

• A. Gases in open systems.
• B. Liquids in special sample holders.
• C. Biological tissues.
• D. Solids (metals, alloys, ceramics, rocks) and prepared powders or coatings; samples should be flat, dry, and representative.

Answer: (D)

In XRF analysis, the most reliable measurements come from solid materials or prepared thin films that present a stable, uniform surface for the X-ray beam. Solids such as metals, alloys, ceramics, and rocks, or prepared powders and coatings that have been dried and made flat, provide a consistent matrix and a defined, representative sampling thickness. This reduces issues like self-absorption, scattering, and geometry errors, so the emitted characteristic X-rays accurately reflect the sample’s elemental composition. Pressed pellets or dried coatings are common preparation methods that help achieve homogeneity and reproducibility, making the results meaningful for a wide range of materials.

Gases in open systems don’t work well because the material density is too low and the fluorescence signal would be very weak, with added difficulties from containment and path length control.

Liquids in special sample holders can be measured in some setups, but they’re not typical due to evaporation risks, nonuniform distribution, and added geometry complications that affect accuracy.

Biological tissues present additional challenges from complex organic matrices and varying thicknesses, requiring special calibration or digestion steps, so they’re not considered standard for routine XRF.

So, solids and prepared powders or coatings that are flat, dry, and representative are the typical suitable samples for XRF analysis.