Sponsored by Specac LtdReviewed by Maria OsipovaJul 2 2024
In analytical chemistry, sample preparation is often an underappreciated aspect of getting the best results. This is particularly accentuated in X-Ray Fluorescence (XRF) analysis. The technique's sensitivity to diverse sample preparation methodologies necessitates rigorous training for analysts, as different preparations can yield both qualitatively and quantitatively different results.
Methods of Sample Preparation for XRF
Four principal methods govern the preparation of samples for XRF analysis, each representing a different trade-off between analytical quality and speed/cost of preparation.
No Preparation:
Direct introduction of the sample, a method characterized by its simplicity.
Loose Powder:
Sample introduced in powdered form, resulting from crushing, milling, and or grinding of the original material.
Pressed Pellets:
A method involving the compression of powdered materials into solid pellets, offering an intermediate ground in terms of analytical quality and expeditious result generation.
Fused Beads:
Employed when the elimination of interferences arising from distinct crystal structures is imperative for a rigorous analysis.
Pressed pellets occupy a middle ground between fused beads and loose powders, enhancing analytical outcomes by compacting powdered materials into a solid, void-free form. This reduces variations in distance to the detector, reduces scattered background, and improves the detection sensitivity for low atomic weight elements.
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Major and Minor Constituents
The analytical scrutiny of both major and minor constituents within a sample would be needed for a complete characterization of a sample. Preparations beyond simple loose powders, including pressed pellets, make it more likely that the minor constituents of a sample will be detected and accurately quantified. Fused beads give this advantage too, albeit the dilutions required may counteract this aim somewhat.
Furthermore, the characteristic X-rays emerge from different depths in the sample, and are generally further penetrating for heavier elements, emitting higher energy characteristic wavelengths. Lighter elements, with longer, lower energy wavelengths, pose challenges in loose powder analysis due to sample inhomogeneity and low density.
Industries Leveraging Pressed Pellets in XRF Analysis
Cement Industry
Cement, as a foundational building material, mandates meticulous quality control. XRF spectroscopy emerges has been important to monitor cement production, facilitating rapid and accurate analysis at various stages of the manufacturing process. Standard methods, such as the ASTM C114 standard, are available to standardise the reporting of these results.
Steel Production: Slag Composition and Control
The composition of blast furnace slag is of great importance in steel production, and can be affected by both the operating conditions and the feed material. XRF spectrometers are again pivotal tools for the elemental analysis of slag, contributing to quality and process control.
Dairy Industry: Nutritional Analysis
While not yet pervasive, X-Ray Fluorescence analysis exhibits promise in the dairy industry for nutritional analysis. The method's potential lies in its ability to analyze dried samples directly without chemical treatment, offering a non-destructive and readily available analytical approach.
Equipment for Pressing Pellets
To press powder into pellets a hydraulic press and a pellet die is needed. The pellet die is usually a block with a cylindrical bore that contains the powders to be pressed. A plunger is driven into the bore to compress the powders using a force applied by the hydraulic press. Various designs facilitate removal of the solid pellet formed in the procedure.
The state-of-the-art APEX 400 press from Specac is available for benchtop laboratory applications where samples need to be produced at rates that exceed more than a few tens per shift. It features semi-automatic programming, options to use both standard and ‘ring’ dies, and an ergonomic layout for use over long shifts. The full range of Specac presses includes manual hydraulic presses for lighter workloads and a complete range of pellet dies.
In conclusion, XRF spectrometry, with its array of sample preparation methods, emerges as a versatile analytical tool catering to diverse industries, each with distinct compositional imperatives. The ongoing exploration of its potential in nutritional analysis underscores its adaptability and continual relevance in scientific inquiry.
This information has been sourced, reviewed and adapted from materials provided by Specac Ltd.
For more information on this source, please visit Specac Ltd.