Excellence in fpXRF: How to be assured you’re getting good quality data using field-portable XRF instrumentation

CIM Montreal 2015
Britt Bluemel (REFLEX Instruments North America)
The increased prevalence of field-portable XRF (fpXRF) instruments in mineral exploration has been a boon for explorers across the globe for a host of commodities. Their use has increased significantly in the past 5 years, and the advent of new high count-rate detectors in 2012 has made analyses available in a fraction of the time required previously. As well as technological advances, increases in the number of suppliers and manufacturers has competitively lowered the price of leasing or purchasing a fpXRF instrument for any stage of project. Real-time chemical analysis is now a feature observed in all stages of the minerals industry, from grassroots projects to operating mines. They are extraordinarily powerful tools, but with great power comes great responsibility, and that responsibility falls mainly on the operator.
Sample collection, preparation, presentation and instrument settings are critical to acquiring a good quality reliable analysis. Implementation of a thorough QA/QC protocol, to assess contamination, accuracy and precision, is often overlooked. Accuracy can be adjusted by post-process calibration, provided the precision is acceptable and a sufficient number of appropriate certified reference materials have been included in the analytical sequence, but it is critical to ensure adequate precision is obtained at the time of analysis.
Since XRF is a “total” analysis, the results from some elements will not be directly comparable to those obtained through traditional wet chemistry digestions (such as a 4-acid digest) from the lab, and in particular, results obtained by aqua regia will be quite different from those same elements by XRF, because it does not break down silicates. Some elements, such as the high field-strength elements (eg. Zr), are notoriously under-represented in wet chemistry, unless a fusion step is undertaken first.
So how can you use a fpXRF to get numbers you can trust? Successful use of a fpXRF on any project, regardless of the end goal, requires thoughtful preparation, including fit-for-purpose matrix-matched standards, duplicates, and blanks; and realistic expectations and knowledge of the limitations of the instrument and resulting data.
Keywords: precision, data quality, accuracy, XRF
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