NITON Sample Analysis Via Energy Dispersive X-Ray Fluorescence (EDXRF)
NITON's hand-held energy-dispersive x-ray fluorescence (EDXRF)
analysers are able to quickly, non-destructively determine the heavy
elemental composition of:
Up to 30 or more elements may be quantified simultaneously by measuring the characteristic fluorescence x-rays emitted by a sample. NITON x-ray fluorescence (XRF) analysers quantify elements ranging from sulphur (element number 16 in the periodic table) through uranium (element number 92) to the heaviest transuranic elements, measuring fluorescent x-ray energies from two thousand electron volts (2 keV) up to 100 keV. In certain specialized laboratory applications, NITON XRF analysers can also measure x-rays of less than 1.5 keV energy in order to quantify elements as light as aluminum and silicon (elements 13 and 14). NITON analysers also measure the elastic (Raleigh) and inelastic (Compton) scatter x-rays emitted by sample during each measurement to determine, among other things, the approximate density and percentage of the light elements in the sample.
How does EDXRF work? Each of the atomic elements present in a sample produces a unique set of characteristic x-rays that is a fingerprint for that specific element. EDXRF analysers determine the chemistry of a sample by measuring the spectrum of the characteristic x-rays emitted by the different elements in the sample when it is illuminated by high energy photons (x-rays or gamma rays). A fluorescent x-ray is created when a photon of sufficient energy strikes an atom in the sample, dislodging an electron from one of the atom's inner orbital shells (lower quantum energy states). The atom regains stability, filling the vacancy left in the inner orbital shell with an electron from one of the atom's higher quantum energy orbital shells. The electron drops to the lower energy state by releasing a fluorescent x-ray, and the energy of this fluorescent x-ray (typically measured in electron volts, eV) is equal to the specific difference in energy between two quantum states of the dropping electron.
Click on image to enlarge
Because the quantum states of each electron orbital shell in each different type of atom (each of the atomic elements) is different, the energies of the fluorescent x-rays produced by different elements are also different: When a sample is measured via XRF, each element present in the sample emits its own unique fluorescent x-ray energy spectrum. By inducing and measuring a wide spectrum of the range of different characteristic fluorescent x-rays emitted by the different elements in the sample, NITON's hand-held XRF analysers can rapidly determine the elements present in the sample and their relative concentrations,in other words, the elemental chemistry of the sample. For samples with known ranges of chemical composition, such as common grades of metal alloys, NITON analysers can also identify many sample types by name, typically in seconds.
It is important to note that, except in special circumstances, light elements cannot be measured directly with portable XRF analysers, simply because x-rays with energies below 2 eV - including the characteristic x-rays of all elements lighter than sulpur (element 16) - are largely absorbed in air within a short distance. For this reason, light element XRF analysis is best performed in a vacuum chamber in a laboratory environment. In those tightly controlled lab conditions, XRF may be used to measure elements as light as beryllium and boron (elements 3 and 4) in highly uniform samples.
Click on image to enlarge
Although NITON's portable XRF analysers have inherent limitations in their ability to measure light elements, NITON XRF analysers automatically compensate for many other effects that would otherwise bias or distort sample analyses. These effects include:
By automatically adjusting for these effects, NITON XRF analysers are able to determine the chemistries of samples of widely different sample compositions, typically in seconds, without any requirement for instrument users to input empirical, sample specific calibrations.
In typical samples containing many elements, the elements may range in concentrations from high percent levels down to parts per million (ppm). In sample matrices such as typical mining samples, metal and precious metal alloys, it is necessary to measure both lighter elements that emit lower energy x-rays (that are easily absorbed) as well as heavier elements that emit much higher energy x-rays (that penetrate comparatively long distances through the sample). Compensations must be made for a variety of geometric effects. In these multi-element samples,it is moreover also typically the case that one or more elements are present that act as critical absorbers or other, heavier elements in the sample. When the characteristic x-rays are quenched, and at the same time, characteristic x-rays of the critical absorber element are emitted. The effects of absorption and secondary fluorescence very widely depending on the chemistry of the sample matrix, but in a sample with many elements in substantial concentrations, multiple absorptions, secondary and also tertiary x-ray fluorescence effects are typically present.
Click image to enlarge
NITON XRF analysers compensate for all of these effects in order to deduce the actual concentration of elements in such multi-element samples from the distorted fluorescenct x-ray spectrum that these samples produce in the XRF analyser. NITON analysers employ multiple methods to determine the true composition of multi-element samples from their x-ray spectra. These include:
In the first empirical testing mode used in NITON XRF analysers, the instrument user teaches a sample to the instrument with a one-minute measurement. The sample is named by the user and the sample's x-ray spectrum is stored in a dedicated library in the analyser that can hold hundreds of these spectra. When an unknown sample is measured in this mode, the new spectrum is compared to the taught spectra stored in the library via least-squares fit analyses. If the new sample spectrum meets the specific sample-matching criteria (defined by the user) for one of the stored sample spectra, the new sample is matched and identified by the given name of that stored sample. This signature-match mode is similar conceptually to doing fingerprint analysis.
In a second empirical testing mode, the NITON instrument operator again teaches a sample x-ray spectra to the analyser and names the sample; then the user directly inputs a known (e.g. lab certified) chemical composition of the sample into the instrument. The sample name, spectrum and chemistry are stored in a separate dedicated library. When an unknown sample is measured in this mode, the sample spectrum is compared to the sample spectra stored in this library. In this mode, the unknown sample chemistry is calculated via extrapolation and interpolation from the stored chemistries of the named samples in the library and the calculated chemistry is then compared to a stored grade look up table of chemical compositions. Empirical testing modes are well suited for measuring samples for which the chemical compositions are reasonably well known in advance.
Compton normalization XRF techniques provide the best results for a wide range of environmental testing and many mining applications: whenever it is necessary to measure sub-percent concentrations of heavy elements in samples composed mainly of light elements. In environmental testing projects, it is often highly desirable to be able to quickly measure low concentration levels of all of the eight Resource Conservation and Recovery Act (RCRA) heavy metals on site and in real time. Using Compton normalization, NITON XRF analysers can measure concentrations of heavy metals such as lead, mercury and cadmium at concentrations below 25 ppm in prepared soil samples. In contrast, detection limits are much worse for all elements in non-homogeneous, and especially in layered samples, such as lead-based paint. NITON has developed advanced, patented methods for the analysis of lead paint and other problematic sample types.
For measuring samples of unknown chemical composition in which concentrations of light and heavy elements may vary from ppm to high percent levels, Fundamental Parameters (FP) analysis is used in conjunction with Compton normalization to simultaneously compensate for a wide variety of geometric effects (including small and odd-shaped samples), plus x-ray absorption, secondary and tertiary fluorescence effects. FP is the preferred analysis tool for mining, precious metals and the majority of metal alloy testing applications. Using this powerful technique, NITON XRF analysers are factory calibrated, a NITON analyser can then measure the full range of element concentrations of all these elements in a wide variety of samples for years without any additional calibrations or user input of any kind.
NITON XRF analysers make their users more productive
Because of FP analysis and other advanced technology, in a variety of testing applications, NITON users require little if any specialized knowledge or laboratory training to work effectively in the field. In industries like mining and mineral exploration this allows the use of relatively low cost workers without degrees in analytical chemistry or geology. In metal and precious metal analysis, the NITON XRF analyser's standard FP analysis can be used in combination with built in grade-identification libraries that enable the NITON user to identify hundreds of metal and/or precious metal alloy grades in seconds.
NITON uses advanced technology to make the company's instruments as fast and easy to use as possible. At the same time, for specialized applications in the mining and metal alloy analysis field that require both the testing of samples with unknown, highly variable chemistries and very accurate measurements of some or all of the elements in the samples, NITON's new XRF analysers can be operated using a combination of FP and user-defined empirical analysis that enables skilled users to optimize the calibration of their instruments in the field to measure specific types of samples.
- » Metal and precious metal samples
- » Rocks and soil
- » Slurries and liquid samples
- » Painted surfaces, including wood, concrete, plaster, drywall and other building materials
- » Dust collected on wipe samples
- » Airborne heavy elements collected on filters.
Up to 30 or more elements may be quantified simultaneously by measuring the characteristic fluorescence x-rays emitted by a sample. NITON x-ray fluorescence (XRF) analysers quantify elements ranging from sulphur (element number 16 in the periodic table) through uranium (element number 92) to the heaviest transuranic elements, measuring fluorescent x-ray energies from two thousand electron volts (2 keV) up to 100 keV. In certain specialized laboratory applications, NITON XRF analysers can also measure x-rays of less than 1.5 keV energy in order to quantify elements as light as aluminum and silicon (elements 13 and 14). NITON analysers also measure the elastic (Raleigh) and inelastic (Compton) scatter x-rays emitted by sample during each measurement to determine, among other things, the approximate density and percentage of the light elements in the sample.
How does EDXRF work? Each of the atomic elements present in a sample produces a unique set of characteristic x-rays that is a fingerprint for that specific element. EDXRF analysers determine the chemistry of a sample by measuring the spectrum of the characteristic x-rays emitted by the different elements in the sample when it is illuminated by high energy photons (x-rays or gamma rays). A fluorescent x-ray is created when a photon of sufficient energy strikes an atom in the sample, dislodging an electron from one of the atom's inner orbital shells (lower quantum energy states). The atom regains stability, filling the vacancy left in the inner orbital shell with an electron from one of the atom's higher quantum energy orbital shells. The electron drops to the lower energy state by releasing a fluorescent x-ray, and the energy of this fluorescent x-ray (typically measured in electron volts, eV) is equal to the specific difference in energy between two quantum states of the dropping electron.
;)
Click on image to enlarge
Because the quantum states of each electron orbital shell in each different type of atom (each of the atomic elements) is different, the energies of the fluorescent x-rays produced by different elements are also different: When a sample is measured via XRF, each element present in the sample emits its own unique fluorescent x-ray energy spectrum. By inducing and measuring a wide spectrum of the range of different characteristic fluorescent x-rays emitted by the different elements in the sample, NITON's hand-held XRF analysers can rapidly determine the elements present in the sample and their relative concentrations,in other words, the elemental chemistry of the sample. For samples with known ranges of chemical composition, such as common grades of metal alloys, NITON analysers can also identify many sample types by name, typically in seconds.
It is important to note that, except in special circumstances, light elements cannot be measured directly with portable XRF analysers, simply because x-rays with energies below 2 eV - including the characteristic x-rays of all elements lighter than sulpur (element 16) - are largely absorbed in air within a short distance. For this reason, light element XRF analysis is best performed in a vacuum chamber in a laboratory environment. In those tightly controlled lab conditions, XRF may be used to measure elements as light as beryllium and boron (elements 3 and 4) in highly uniform samples.
;)
Click on image to enlarge
NITON sample analysis techniques
Although NITON's portable XRF analysers have inherent limitations in their ability to measure light elements, NITON XRF analysers automatically compensate for many other effects that would otherwise bias or distort sample analyses. These effects include:
- » Geometric effects caused by the sample's shape, surface texture, thickness and density.
- » Spectroscopic interferences and other sample matrix effects.
- » Critical absorption of the characteristic x-rays of one element by other elements in the sample, and secondary and tertiary x-ray excitation of one or more elements by other elements in the sample.
By automatically adjusting for these effects, NITON XRF analysers are able to determine the chemistries of samples of widely different sample compositions, typically in seconds, without any requirement for instrument users to input empirical, sample specific calibrations.
In typical samples containing many elements, the elements may range in concentrations from high percent levels down to parts per million (ppm). In sample matrices such as typical mining samples, metal and precious metal alloys, it is necessary to measure both lighter elements that emit lower energy x-rays (that are easily absorbed) as well as heavier elements that emit much higher energy x-rays (that penetrate comparatively long distances through the sample). Compensations must be made for a variety of geometric effects. In these multi-element samples,it is moreover also typically the case that one or more elements are present that act as critical absorbers or other, heavier elements in the sample. When the characteristic x-rays are quenched, and at the same time, characteristic x-rays of the critical absorber element are emitted. The effects of absorption and secondary fluorescence very widely depending on the chemistry of the sample matrix, but in a sample with many elements in substantial concentrations, multiple absorptions, secondary and also tertiary x-ray fluorescence effects are typically present.
;)
Click image to enlarge
NITON XRF analysers compensate for all of these effects in order to deduce the actual concentration of elements in such multi-element samples from the distorted fluorescenct x-ray spectrum that these samples produce in the XRF analyser. NITON analysers employ multiple methods to determine the true composition of multi-element samples from their x-ray spectra. These include:
- » A variety of user-definable empirical calibrations.
- » Real-time Compton normalization.
- » Fundamental Parameters analysis.
- » Various combinations of these techniques.
In the first empirical testing mode used in NITON XRF analysers, the instrument user teaches a sample to the instrument with a one-minute measurement. The sample is named by the user and the sample's x-ray spectrum is stored in a dedicated library in the analyser that can hold hundreds of these spectra. When an unknown sample is measured in this mode, the new spectrum is compared to the taught spectra stored in the library via least-squares fit analyses. If the new sample spectrum meets the specific sample-matching criteria (defined by the user) for one of the stored sample spectra, the new sample is matched and identified by the given name of that stored sample. This signature-match mode is similar conceptually to doing fingerprint analysis.
In a second empirical testing mode, the NITON instrument operator again teaches a sample x-ray spectra to the analyser and names the sample; then the user directly inputs a known (e.g. lab certified) chemical composition of the sample into the instrument. The sample name, spectrum and chemistry are stored in a separate dedicated library. When an unknown sample is measured in this mode, the sample spectrum is compared to the sample spectra stored in this library. In this mode, the unknown sample chemistry is calculated via extrapolation and interpolation from the stored chemistries of the named samples in the library and the calculated chemistry is then compared to a stored grade look up table of chemical compositions. Empirical testing modes are well suited for measuring samples for which the chemical compositions are reasonably well known in advance.
Compton normalization XRF techniques provide the best results for a wide range of environmental testing and many mining applications: whenever it is necessary to measure sub-percent concentrations of heavy elements in samples composed mainly of light elements. In environmental testing projects, it is often highly desirable to be able to quickly measure low concentration levels of all of the eight Resource Conservation and Recovery Act (RCRA) heavy metals on site and in real time. Using Compton normalization, NITON XRF analysers can measure concentrations of heavy metals such as lead, mercury and cadmium at concentrations below 25 ppm in prepared soil samples. In contrast, detection limits are much worse for all elements in non-homogeneous, and especially in layered samples, such as lead-based paint. NITON has developed advanced, patented methods for the analysis of lead paint and other problematic sample types.
For measuring samples of unknown chemical composition in which concentrations of light and heavy elements may vary from ppm to high percent levels, Fundamental Parameters (FP) analysis is used in conjunction with Compton normalization to simultaneously compensate for a wide variety of geometric effects (including small and odd-shaped samples), plus x-ray absorption, secondary and tertiary fluorescence effects. FP is the preferred analysis tool for mining, precious metals and the majority of metal alloy testing applications. Using this powerful technique, NITON XRF analysers are factory calibrated, a NITON analyser can then measure the full range of element concentrations of all these elements in a wide variety of samples for years without any additional calibrations or user input of any kind.
NITON XRF analysers make their users more productive
Because of FP analysis and other advanced technology, in a variety of testing applications, NITON users require little if any specialized knowledge or laboratory training to work effectively in the field. In industries like mining and mineral exploration this allows the use of relatively low cost workers without degrees in analytical chemistry or geology. In metal and precious metal analysis, the NITON XRF analyser's standard FP analysis can be used in combination with built in grade-identification libraries that enable the NITON user to identify hundreds of metal and/or precious metal alloy grades in seconds.
NITON uses advanced technology to make the company's instruments as fast and easy to use as possible. At the same time, for specialized applications in the mining and metal alloy analysis field that require both the testing of samples with unknown, highly variable chemistries and very accurate measurements of some or all of the elements in the samples, NITON's new XRF analysers can be operated using a combination of FP and user-defined empirical analysis that enables skilled users to optimize the calibration of their instruments in the field to measure specific types of samples.
Niton UK Limited | Unit 19 The Calvert Centre, SO21 3BN | Tel: 01256 397860 | Fax: 01256 397861
