Would you accept results from an assay laboratory that doesn’t use standards, duplicates, or blanks? Your answer should be an empathetic no! You should treat your pXRF analysis the same way otherwise; with no standard Certified Reference Materials (CRM) to compare to, it is just a random number generator.
Why should I use CRMs?
For users of portable X-ray fluorescence (pXRF) instruments, routine analysis of CRMs can provide a baseline performance of the instrument and monitor the quality of your results during the sampling program. This allows the user to quantify the accuracy and precision of the results and check whether post-processing is necessary.
Why does the result from my pXRF not match that from the CRM?
Firstly, manufacturers calibrate instruments to give an approximate result across the entire matrix types; they are unlikely to give you an exact result for your particular geologic environment.
As well, CRMs are certified using a different assay method to the portable XRF method, so they should only be used as a guide. If aqua regia is used in the certification of the CRM, then this will differ from the pXRF result as it only provides the total soluble analysis. Fusion XRF and ICP-MS correlate better with pXRF but again may not be suitable for all elements.
Where can I get CRMs?
Portable XRF Services sell a variety of CRMs in pXRF cups that cover a wide variety of matrices, elements and element concentrations.
Can I develop my own calibration using CRMs?
Custom calibrations developed for a specific geologic environment can give increased accuracy and precision than a manufacturer calibration. A custom calibration can be created by obtaining CRMs suitable for your environment and/or creating CRMs using your laboratory assay results. Portable XRF services is a certified Bruker custom calibration provider and can develop a calibration specific to your geologic environment.
How do I use CRMs with pXRF to get the best result?
- Use a variety of CRMs to assess and monitor the performance of your instrument
- Use the CRMs to check that your pXRF can detect the elements of interest and within the concentration range of interest
- Analyse a CRM and blank every 20 to 30 samples.
- Monitor the expected result for an element(s) of interest in the CRM to maintain confidence in the results
- Use a quartz blank to monitoring low level contamination in the tube of the instrument
By keeping these points in mind you can be sure that your pXRF is fit for purpose and gain confidence in the results.