X-Ray Fluoresence (XRF)

XRF is an elemental analysis technique with unique capabilities including (1) highly accurate determinations for major elements and (2) a broad elemental survey of the sample composition without standards.  For example, XRF is used in analysis of rocks and metals with an accuracy of ~0.1% of the major elements.  A technique known as Fundamental Parameters can estimate the elemental composition of unknowns without standards.  And to top it all off, sometimes the analysis requires minimal sample preparation.  

Exova offers X-Ray Fluorescence at our Missisauga location. Detection limits for XRF are generally in the 10-100 ppm range for heavy elements, and elements lighter than Na are difficult or impossible to detect.  Our Rigaku ZSX can analyze elements B-U, except N and O. 

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How does X-Ray work?

X-Ray Scans

Sample Spot Analysis and 3-D Element Mapping

Quantitative Analysis by XRF

Comparison of XRF-SQX and ICPMS Metals Screen

Examples of XRF-SQX Analysis

Rigaku ZSX100e XRF

ZSX100e XRF


How does XRF work?

High energy photons (x-rays) displace inner shell electrons.  Outer shell electrons then fall into the vacancy left by the displaced electron.  In doing so, they normally emit light (fluoresce) equivalent to the energy difference between the two states.  

Since each element has electrons with more or less unique energy levels, the wavelength of light emitted is characteristic of the element.  And the intensity of light emitted is proportional to the elements concentration.

Note that this is a highly simplified explanation.  

XRF Process (from Rigaku)

There are generally two types of XRF spectrometers: wavelength dispersive and energy dispersive.  Wavelength dispersive system uses a diffraction crystal to focus specific wavelengths onto a detector.  A wavelength range is scanned by changing the angle in which the x-rays strike the crystal.  An energy 

dispersive spectrometer focuses all the emitted x-rays onto an energy analyzing detector.  While this is faster and less expensive, wavelength dispersive spectrometers are more sensitive and have higher resolution. For this reason we've chosen a wavelength dispersive system.

X-Ray Scans

As the diffraction crystal is rotated during a scan, x-ray emission lines of various elements are focused on the detector.  The figure below shows a scan using the standard LiF diffraction crystal and the SC detector.  The angle of diffraction (2-theta) is plotted against the detector response.

The broad emission band at 8-30o and the lines near 15-20o are due to x-rays from the x-ray excitation source which contains a Rh target in this case scattered by the sample. Other lines such as those for Fe are from the sample.  

X-ray emission lines are commonly referred to KA, KB, LA, or LB. K and L refers to the electron shell vacancy being filled, and the A and B refer to the source from which the electron originates.  A is from the nearest shell, and B is from the next shell further out.  For the Fe emission lines, the KA emission represents the x-ray energy emitted when an L electron falls into a vacancy in the K shell.  The Fe-LB line represents the x-ray emission from an M shell electron moving into a K vacancy. 

Qualitative X-Ray Fluorescence Scan

XRF Qualitative Scan


Sample Spot Analysis and 3-D Element Mapping  

Elements in samples can be mapped, or small spots (0.5 mm) can be analyzed.  A camera in the analysis chamber allows the precise alignment of the sample for analysis.

In the figures below, the xrf analysis was conducted on a 2 mm square area  of the sample outlined in red containing a foreign substance.  A spot analysis of the foreign material revealed that the substance was primarily Al.  The 3-dimensional map shows the distribution of Al in that 2 mm square area.

Sample with foreign material identified as Al

2 mm Area mapped for Al


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Exova

9240 Santa Fe Springs Rd
Santa Fe Springs, CA 90670
562.948.2225   Fax 562.948.5850
info400@exova.com

Exova

Formerly West Coast Analytical Service (WCAS) and Bodycote Testing Group