Evaluate your analysis...

Advances in both wavelength-dispersive (WDXRF) and energy-dispersive (EDXRF) X-ray fluorescence instrumentation enable us to run analysis on almost any types of samples. However, there is a big difference between just running an analysis and producing solid quantifiable results that are repeatable.

The lack of proper sample preparation can account for as much to 30% of inaccurate results (Pederson & Wismann, 1997). There is a balance, mostly due to a time compromise, that must be made between quick analysis and optimum results. I’ve encountered many sites that a few simple tweaks to preparation steps, could improve their results significantly without taking too much additional time. But do they really? I find it best practice not to take short cuts especially when ensuring the best possible quality analysis.

Here are a just a few simple ideas to think about when evaluating your process when using liquids or loose powders:

Film Handling: Keep your fingers away from the center of the film, if you do touch the film surface, throw it away and start again. Your fingers can transfer a range of contaminants which may affect the sensitivity of certain elements, or give you a higher than expected reading on others. It is good practice to wear gloves while handling the film.

Choose your film wisely: Every film type has different properties in terms of transmission and resistance to chemical attack. Just changing your film type could increase your intensity on sodium by up to 50% as noted from the table below. If you are suffering from spilled samples, consider changing to a more resistant film like Mylar.

Table: Comparison of the average transmission % using different film types and an AUSMON Monitor

Never re-use the same sample cell – Occasionally, companies may have processes to empty the old powder, and simply refill the plastic cell with a new sample to save on costs, with no washing or cleaning steps. This creates cross contamination of the samples and can lead to very poor results.

Weigh the sample – Keeping the same sample weight each measurement can dramatically reduce variations in the results. You don’t need to weigh to the 0.001 level of accuracy, but by simply maintaining the weight to a level of +/- 0.1g is a significant improvement. It takes only a little more time, but ensures consistency in your analysis.

When analyzing liquid samples, it’s always good practice to measure them immediately after the sample preparation for practical reasons - they evaporate or chemically attack the film. Both problems will affect the results negatively.

These are just some of the areas to look out for, even though they appear fairly minor steps in the process, they could potentially cost more in the long term. By ensuring you have taken the necessary steps towards proper sample preparation, you can walk away more confident about your analysis. 

Scott is an experienced Product Manager with PANalytical, on the analysis using X-ray Fluorescence (XRF) technology. He is a regular speaker at seminars which help end users to better optimize their XRF technology and software. Do connect with him on LinkedIn if you have a question pertaining to this.  

PANalytical is the world’s leading supplier of instrumentation and software for X-ray diffraction (XRD) and XRF. Our products are widely used for the analysis and characterization of materials ranging from cement, metals, industrial minerals, glass, semiconductors, pharmaceutical solids and many more. Headquartered in the Netherlands, PANalytical has close to 70 years of experience in innovating and delivering precision X-ray instrumentation and software. 

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