Sample Preparation of Powdered Materials for XRF Analysis

Introduction
To obtain reliable and reproducible results by X-ray fluorescence (XRF) analysis, it is crucial that the sample be as compositionally uniform as possible and optimally prepared in terms of structure and surface. This is especially important when working with powdered materials—ranging from ore and coal to pharmaceutical and ceramic mixtures. In this article, we will show how even a complex laboratory procedure can be standardized to strike the right balance between preparation speed and the required analytical accuracy.

Stage 1. Sample Collection and Primary Cleaning

Sampling
Collect sub-samples from multiple points within the extraction zone (e.g., different locations in a mine or quarry) and combine them into a representative composite sample weighing approximately 300 g.

Impurity Removal
Carefully pick out all visible foreign inclusions—fragments of packaging, organic debris, bits of plastic or wood—to eliminate any extraneous components that might distort the fluorescence spectrum.

Tip: Even if your material is already in powder form, inspect it for caking or oversized fragments before proceeding.

Stage 2. Grinding and Homogenization

Coarse and Fine Comminution
If your starting material consists of lumps of ore or coal, perform a two-step comminution: first a coarse crush, then fine grinding in a disk mill.

Particle-Size Control
Achieve a particle size of 30–40 μm. This grain size promotes uniform X-ray absorption and minimizes variations in interaction with the X-ray beam.

Homogenization
Transfer the ground powder repeatedly from one container to another to thoroughly mix it and ensure a consistent composition throughout the entire sample.

Stage 3. Drying and Determining Loss on Ignition (LOI)

Drying
Dry the material in an oven at 100 °C for 2 hours to remove condensed moisture and eliminate the influence of adsorbed water.

Ignition (LOI)
Calcine a portion of the dried sample at 1 000 °C for 1 hour. Measure the mass difference before and after ignition—this value is the Loss on Ignition (LOI). Enter the measured LOI into your XRF analyzer’s settings as a correction factor.

Why It Matters:
Elvatech’s fundamental-parameter algorithms account for every element in the sample. If LOI is not applied as a correction, the “missing” mass will be redistributed among the remaining elements, distorting the final results.

Stage 4. Tablet Pressing for Maximum Accuracy

Mold and Press Setup
Use a hydraulic press capable of applying approximately 10 tons of force, along with a suitable die set.

Pressing
Form a tablet 32 mm in diameter and 2–3 mm thick. Ensure the tablet surface is free of cracks and air inclusions.

Benefit
Minimizing air gaps improves the detection of weak fluorescence lines—especially for elements like sodium and magnesium—critical when their concentrations are low.

Conclusion

Proper sample preparation is the keystone of accurate and precise measurements on any Elvatech XRF spectrometer. For rapid, in-field screening you can simply fill a sample cup and take a quick measurement, but laboratory-grade analysis demands a rigorous workflow: from sampling and cleaning to drying, LOI correction, and tablet pressing. By following these stages, you will produce homogeneous samples and minimize analytical errors—even when analyzing complex aluminosilicates, ores, or other powders.

Want to learn more or test our solutions? Contact us—our specialists will help you choose the right instrument and tailor the procedure to your needs.