Equal concentrations do not always produce equal signals
XRF results depend on the relationship between an elemental signal and the sample’s overall composition. Absorption and enhancement by other elements, as well as thickness, particle size and homogeneity, can change the response. Plastics, soils and metals should not share an unvalidated analytical procedure simply because they contain the same target element. Address matrix effects together with calibration strategy, preparation and intended use.
Calibration and checks have different roles
Calibration establishes the relationship between response and concentration; routine checks monitor whether an established method continues to perform as expected. We recommend managing calibration samples separately from independent check materials and covering the material types and concentration ranges relevant to the work. A high-concentration check alone does not demonstrate adequate capability near a low-level decision boundary. A software notification that calibration is complete cannot replace validation on relevant samples.
Read the certificate before using the material
Check whether the target element has a certified value, its uncertainty, the certification period, storage conditions and preparation requirements. NIST specifically asks users to ensure that they hold the current certificate. Purchasing a reference material does not automatically make every subsequent result traceable; the laboratory still needs to establish a sound measurement process and uncertainty chain. If a material is heterogeneous, a very small measurement area may not represent the bulk material characterized by the certificate.
Investigate trends before adjusting calibration
Maintain a time series of check results linked to maintenance, consumable changes, software versions and sample preparation. If a sustained shift develops, investigate contamination, surface changes, preparation differences and measurement conditions before changing the calibration. Simply adjusting the result back to the certified value can hide a method problem and affect its suitability for other samples.
Reports should preserve the method version, sample condition, scope and relevant uncertainty information. Before comparing instruments or laboratories, check that the measurand, units and preparation conditions agree. Reference materials help a team identify and control bias; their value comes from how they are used within the measurement process.
References
- NIST — Uncertainty and Traceability in Alloy Analysis by Borate Fusion and XRF
- NIST — Study of Microheterogeneity in Solid Reference Materials
- NIST — Standard Reference Materials and current certificates
- NIST — Metrological Traceability
Accessed: September 29, 2026. This article discusses methods and workflows. Apply the practical recommendations in conjunction with applicable standards, contractual requirements and local method validation.