Tech Team · Kintek Solution

Preparing a sample for XRF (X-ray Fluorescence) analysis involves several critical steps to ensure accurate and reliable results. The process typically includes crushing, grinding, and pressing or fusing the sample to create a homogeneous and representative material. Two common methods are pressed pellets and fused beads. Pressed pellets are made by grinding the sample to a fine grain size (<75 µm) and pressing it with a die set, sometimes using a wax binder if the sample lacks binding properties. Fused beads involve mixing the sample with a flux and heating it to high temperatures, though this method may dilute trace elements. For solid samples, achieving a flat and clean surface is essential, as irregular surfaces can introduce errors in the analysis. Loose powdered materials are placed in plastic sample cups with support films, ensuring a flat surface and proper support over the X-ray beam. The sample must be finely ground to achieve homogeneity and meet the infinite thickness requirement for all elements of interest. Special care is needed for metal powders in high-power WDXRF instruments to prevent heating and melting through the support film. Overall, the preparation process aims to produce a robust, homogeneous, and representative sample for accurate XRF analysis.

Key Points Explained:

1. Sample Preparation Methods:

   • Pressed Pellets: This is one of the most common and cost-effective methods. The sample is ground to a fine grain size (<75 µm) and pressed into a pellet using a die set. If the sample lacks binding properties, a wax binder can be added to ensure the pellet holds together. This method is popular due to its high-quality results, speed, and low cost.
   • Fused Beads: This method involves mixing the sample with a flux and heating it to high temperatures to create a homogeneous bead. While this method can produce highly accurate results, it may dilute trace elements, making it less suitable for certain analyses.

2. Solid Sample Preparation:

   • Surface Flatness: An ideal solid sample for XRF analysis should have a perfectly flat surface. Irregular surfaces can alter the distance from the sample to the X-ray source, introducing errors in the analysis. XRF systems are calibrated based on a fixed sample-to-source distance, and any deviation can affect the intensity of the elements detected.
   • Surface Cleaning and Polishing: The sample surface must be clean and smooth. For hard metals, grinding tools are used, while soft metals may require lathes. Separate files should be used for different sample types to avoid cross-contamination.

3. Loose Powder Preparation:

   • Sample Cups: Loose powdered materials are typically placed into plastic sample cups with a plastic support film. This ensures a flat surface and proper support over the X-ray beam.
   • Grinding and Homogeneity: The sample should be finely ground to achieve homogeneity and limit void spaces. Using approximately 15g of sample is usually sufficient to meet the infinite thickness requirement for all elements of interest.
   • Special Considerations for Metal Powders: In high-power WDXRF instruments, metal powders require special care to prevent the sample from heating up and melting through the support film.

4. General Steps for Sample Preparation:

   • Crushing and Grinding: The fundamental steps for preparing materials for XRF analysis include crushing and grinding the sample to achieve a fine and homogeneous powder.
   • Pressing or Fusing: After grinding, the sample is either pressed into a pellet or fused into a bead, depending on the chosen preparation method.

5. Handheld XRF Process:

   • Emission: The analyzer emits X-rays.
   • Excitation: The X-rays hit the sample, causing it to fluoresce and send X-rays back to the analyzer.
   • Measurement: The detector measures the energy spectrum, identifying which elements are present and their quantities.
   • Analysis: The results are used for various applications such as material verification, scrap recycling, and environmental assessments.

By following these steps and considerations, you can prepare a sample that is suitable for XRF analysis, ensuring accurate and reliable results.

Summary Table:

Step	Description
Crushing & Grinding	Reduce the sample to a fine, homogeneous powder (<75 µm).
Pressed Pellets	Press the ground sample into a pellet using a die set; add wax binder if needed.
Fused Beads	Mix the sample with flux and heat to create a homogeneous bead.
Solid Sample Prep	Ensure a flat, clean surface; use grinding tools or lathes for polishing.
Loose Powder Prep	Place powder in sample cups with support films; grind finely for homogeneity.
Special Considerations	Handle metal powders carefully to avoid melting through support films.

Ensure accurate XRF analysis results—contact our experts today for guidance on sample preparation!