Advancements in both wavelength dispersive (WD) and energy dispersive (ED) X-ray fluorescence instrumentation, enable us to run analyses on almost all types of sample materials. There is a big difference between just running an analysis and producing solid quantifiable results that are repeatable though.
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 suggested simple tweaks to preparation steps which could improve their results significantly without taking too much additional time.
But do they? I find it best practice not to take shortcuts, 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 to 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.
- 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 for 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 analyses.
- When analyzing liquid samples, it’s always good practice to measure them immediately after the sample preparation for practical reasons – they can evaporate or chemically attack the film. Both of these actions will affect the results negatively.
These are just a few points 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 will be able to be more confident about your analyses.
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