Which statement best describes typical XRF sample surface preparation?

• A. Gases are ideal samples with no preparation.
• B. Liquids are always unsuitable for XRF.
• C. Solids (metals, alloys, ceramics, rocks) and prepared powders or coatings, flat and dry, are typical; samples should be representative.
• D. Only biological tissues are suitable.

Answer: (C)

In XRF surface preparation, the goal is to have a flat, dry, representative surface so the measured X-ray signal truly reflects the material being analyzed. The XRF signal comes from the material’s near-surface region, so roughness, moisture, or uneven geometry can distort results. Therefore, typical samples are solids such as metals, alloys, ceramics, and rocks, prepared as flat, smooth surfaces or as prepared powders or coatings that form a uniform, even layer. Pressed pellets or coated films of powders are common to achieve consistency in thickness and composition across the analyzed area, ensuring the sample area examined represents the material as a whole.

Gases are not the standard form for routine XRF analysis and usually require specialized setups. Liquids can pose challenges due to spreading, drying, or absorption effects, so they are not the typical default but may be accommodated with appropriate preparation. Biological tissues fall outside the common, representative solids used for general XRF analysis.