Tech Team · Kintek Solution

Preparing samples for X-ray fluorescence (XRF) analysis involves several methods tailored to the type of sample being analyzed, whether solid, powdered, or liquid. The goal is to ensure the sample is homogeneous, flat, and free of contaminants to achieve accurate and reliable results. Common techniques include pressed pellets, fused beads, and direct measurement of powders or liquids. Each method has specific steps and considerations, such as grinding samples to a fine powder, using binding agents, or selecting appropriate films for liquid samples. The choice of preparation method depends on the sample's properties and the desired analytical precision.

Key Points Explained:

1. Pressed Pellets for Solid and Powdered Samples:

   • Pressed pellets are one of the most common and cost-effective methods for preparing solid and powdered samples for XRF analysis.
   • The process involves grinding the sample to a fine powder, typically with a grain size of <75 µm, to ensure homogeneity.
   • A binding agent, such as cellulose or boric acid, may be added to improve pellet formation and stability.
   • The powdered sample is then pressed into a pellet using a die set. If the sample lacks natural binding properties, a wax binder can be used.
   • This method is favored for its speed, low cost, and ability to produce high-quality results.

2. Surface Preparation for Solid Samples:

   • For solid samples, the surface must be flat, smooth, and clean to ensure accurate XRF measurements.
   • Preparation involves polishing the sample using tools like grinding tools for hard metals or lathes for soft metals.
   • Separate files or tools should be used for different sample types to avoid cross-contamination.
   • Cleaning the surface thoroughly is essential to remove any contaminants that could interfere with the analysis.

3. Preparation of Geological Samples:

   • Geological samples often contain hard and brittle minerals, making them challenging to prepare.
   • These samples are typically ground into a very fine powder and mixed with a binding agent to improve pellet formation.
   • Binding agents like cellulose or boric acid help lubricate the particles and ensure they adhere properly during pressing.
   • The resulting pellets are uniform and suitable for XRF analysis.

4. Direct Measurement of Powdered Samples:

   • For powdered samples, direct measurement is the simplest and most common preparation method.
   • The sample is ground to achieve a homogeneous mixture with an optimal grain size of <75 µm.
   • The powder is poured into a cuvette, and the surface is leveled to ensure it is flat and even for measurement.
   • This method is quick and effective, especially for samples that do not require additional binding agents.

5. Liquid Sample Preparation:

   • Liquid samples are prepared by pouring the liquid into a specialized cup and sealing it with a film.
   • The film must provide adequate support and transmission while preventing contamination of the sample.
   • Choosing the right film material is crucial to ensure accurate XRF analysis of liquid samples.

6. Fused Beads for Trace Element Analysis:

   • Fused beads are another preparation method, particularly useful for trace element analysis.
   • The sample is mixed with a flux, such as lithium tetraborate, and heated to high temperatures to form a glass-like bead.
   • While this method dilutes trace elements, it ensures a homogeneous sample and is ideal for certain types of analysis.

7. Other Preparation Techniques:

   • Additional methods include powder compacting, plastic ring compacting, boric acid rimmed priming compacting, and steel ring compacting.
   • These techniques offer flexibility depending on the sample type and analytical requirements.

By following these preparation methods, samples can be optimized for XRF analysis, ensuring accurate and reliable results. Each method has its advantages and is chosen based on the sample's characteristics and the specific analytical goals.

Summary Table:

Sample Type	Preparation Method	Key Steps
Solid/Powdered	Pressed Pellets	Grind to <75 µm, add binding agent, press into pellet.
Solid	Surface Preparation	Polish to a flat, smooth surface; clean thoroughly.
Geological	Pressed Pellets	Grind finely, mix with binding agent, press into pellet.
Powdered	Direct Measurement	Grind to <75 µm, pour into cuvette, level surface.
Liquid	Liquid Sample Preparation	Pour into cup, seal with appropriate film.
Trace Elements	Fused Beads	Mix with flux, heat to form glass-like bead.
Other	Various Compacting Methods	Use powder, plastic, or steel ring compacting based on sample type.

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