X-Ray Fluorescence FAQ

In practice from fluorine to uranium, 72 elements can be analyzed with XRF; almost the entire periodic table of elements, which is the reason for the widespread use of this technique.  

With EDXRF, the sample is excited by the X-ray tube directly or through a filter. A semiconductor detector analyzes the X-ray fluorescence radiation that comes directly from the sample.

Here, the detector together with the associated electronics counts and sorts, according to energy, all of the photons that reach it. A pulse height spectrum that indicates the number of photons or impulses for a given energy is established. The detector typically has only a few µs for processing, so that processing is accordingly limited to approximately 1,000,000 pulses per second. Using a filter, a portion of the exciting radiation can be screened out to avoid overloading the detector.  

In general, it is possible to say that the two techniques are complimentary; one supplements the other. EDXRF has a time advantage, as all elements are measured simultaneously, whereas the (serial) WDXRF measures the elements one after another. WDXRF has a resolution and sensitivity advantage which is especially useful in the range of atomic numbers up to 30 and from 55 to 80.  

With XRF, most of the elements are only measured on the surface of the sample. This is why the condition of the sample surface with respect to smoothness and homogeneity (surface area and depth) is so essential. In practice, this more or less determines the total analytical error. Thus sample preparation for XRF becomes the most important component of a test method.
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CRM: Certified Reference Material
A CRM is a RM that has been analyzed with a traceable analytical method for one or more parameters. The value of the parameter, the corresponding uncertainty and a statement concerning the metrological traceability are indicated in a certificate.

RM: Reference Material
A sample that is sufficiently homogenous and stable for one or more parameters and that is considered to be suitable for use in a measuring process.

SeRM: Secondary Standard
A sample for which the parameters were assigned using a comparison with a primary measurement standard (e.g., a CRM).  

XRF is characterized by a very high long-term stability. Nevertheless, the components show certain wear effects over time so that the measured signal changes. If the change is known, it can be corrected for using a so-called drift correction.

The drift correction is based on the principle that at the time of the calibration (day 0) and at a given time afterwards (day 1), the same, stable drift correction sample (drift monitor) is measured. The correction is then calculated from the change in the measured signal.    

If a company is accredited, the German accreditation body (DAkkS) has confirmed that it follows certain standards (guidelines) for the areas tested. FLUXANA is accredited according to DIN EN ISO/IEC 17025:2018 (analysis of samples using x-ray fluorescence analysis) and DIN EN ISO 17034:2017 (production of reference materials).   

A round robin or proficiency test is a method for assuring the quality of laboratory analyses. Several laboratories analyse the same sample and compare their analysis results with each other. If a laboratory has outliers in the values of the analysis, this is an indication of methodological or technical errors.

FLUXANA regularly offers round robins.

Drift Monitors: Used to check instrument drift by comparing day 1 result with day 0 result. Mostly intensities are used.
Control Samples: Used to check an application with a sample as a daily check where the result is compared with the known concentrations.
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LOC Samples: LOC=line overlap correction. Single element sample to show and correct line overlaps to other elements which are not present in that sample.
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Setting up SUS: Mostlyused in OES to readjust a calibration by a single point, in XRF miss used for drift monitor or control sample.
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Calibration samples: Used to setup a calibration could be a known sample, a RM or CRM.

Validation sample: Used to validate a calibration, should or must be a CRM to be sure the calibration works. Compared with acontrol sample this is done only after setting up a calibration, not daily. A validation sample must not be used for calibration.