A custom calibration looks holistically at the material of each sample and how the elements interact with each other. Custom calibrations are created using proprietary software that calculates results by incorporating spectral overlaps, escape peaks and sample matrix effects to provide robust sample interpretation. Further, custom calibrations enable additional elements to be included with enhanced precision and accuracy of the results across the full concentration range. Customising a calibration can allow results from the XRF to be more accurate and better compliment the project and/ or material aims.
All calibrations on portable XRF are set up to target elements related to the material being analysed. For instance, the lead in paint calibration targets lead as this is the primary element of interest. When considering the portable XRF, there are so many analytical possibilities as it can analyse glass, wood, lead in paint, silver, gold, Stirling silver, alloys, core, rock chips, low to high density plastic, limestone, sulfur in oil, obsidian, just to name a few! The XRF technique is matrix dependent. That is, the intensity of the sample measured by the XRF is not solely dependent on individual element concentration, but to a rather high degree, the concentrations of other elements that make up the sample.
For example, as discussed by Philip J Potts and Margaret West in Portable X-ray Fluorescence Spectrometry, if you consider two alloys, one with 90% Ni, 10% Fe and another with 60% Ni, 30% Mo, 10% Fe. Despite the iron concentration being identical in both alloys, the signal from iron from both samples will be very different. Rather than incorrectly relying on concentration alone, the XRF calibration accounts for these matrix differences and corrects them in its reporting. It is therefore not surprising that sometimes an off-the-shelf calibration offered by manufacturers is not fit for purpose for the material being analysed, in which case a custom calibration that better fits the matrix interactions would be the best option.
While generic calibrations created by pXRF manufacturers can provide a fantastic base for ready-to-use analysis, there are times that they are not sufficient to meet the data requirements of a specific project. A custom calibration can significantly improve the accuracy of pXRF results where the generic calibrations are not sufficient. Calibrations are customised to the exact mineral matrix of a client’s sample to calculate the required correction due to element overlaps, escape, sum and diffraction peaks and interferences caused by the specific matrix. They reliably cover the full concentration range of critical elements to increase confidence in the results generated by the pXRF. Additionally, creating something custom and targeted to a specific element or material type in turn allows for increased confidence in the results coming from your pXRF and overall project aims. It also ensures all elements reported are relevant, cutting down time spent during data interpretation sifting through irrelevant elements found in generic calibrations.
Calibrations can be generated to cover any element from Mg to U. Sodium (Na) can also be included on the top of the range Bruker TRACER 5g instrument. Calibrations can include as many, or as few elements desired, determined by importance to a project. If the portable XRF can analyse the element, then PSS can calibrate for it.
Custom calibrations are not limited to a single industry or sample type. Suitable sample types include but are not limited to soil, ore material, plastics, welds, plant materials, ceramics and even paints. To create a custom calibration, the client needs to provide Portable Spectral Services with a set of representative samples that have corresponding laboratory assay results. For best results, the samples should be homogenous and cover a good range of elements and concentrations relevant to the client’s project. The resulting custom calibration will be applicable within the ranges defined by the provided reference materials. Additionally, if the calibration samples and instrument are not able to be provided to PSS due to being located remotely, options for off-site calibration can be available upon request.
Once a custom calibration is created, standards are used to check its continued accuracy across time and to monitor for contaminants. These are most often certified reference material (CRM) that have high concentrations of target elements. By monitoring target elements in an established QAQC analysing procedure, it ensures that the custom calibration remains consistent throughout any given project.
Portable Spectral Services is the Bruker Authorised Applications Centre (BA²C) for Australasia. Portable Spectral Services offers custom calibrations on exclusively Bruker portable XRF models including all models of the S1 TITAN, and CounterTop XRF (CTX), and for the TRACER 5 series including models TRACER 5i and TRACER 5g.
Potts, Philip J and Margaret West (eds). Portable X-ray Fluorescence Spectrometry: Capabilities for In Situ Analysis. Cambridge: RSC Publishing, 10.
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