NON DESTRUCTIVE CHEMICAL ANALYSIS
Qualitative, quantitative analysis
and “standardless” analysis
Notes by:
Dr Ivan Gržetić, professor
University of Belgrade – Faculty of Chemistry
Qualitative, quantitative analysis and
“standardless” analysis
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Every element of the periodic system of elements
(except H & He) have its characteristic X-ray
emission lines.
To be sure that we will obtain line of interest the
excitation potential (incident radiation) should be
at least three times greater than the energy of
emission line in question.
For example, if one wants to get Cu Kα line
(8,04keV) than the excitation potential must be
24 kV or greater.
Qualitative, quantitative analysis
and “standardless” analysis
Every producer of SEM-EDS, SEM-WDS, WD-XRF, EDXRF and Handheld ED-XRF has their own program
packages for qualitative, quantitative analysis and
“standardless” analysis. Usually all these packages have
similar purposes, but different names. They are always
protected with trademarks. But, once you get
acquainted with one set of programs produced by one
firm, immediately you gain experience for all of them.
Why? Theoretical and scientific background is always
the same.
 The differences appear only for specialized
requirements set by users like semiconductor industry,
metallurgy, environmental science, inspections, etc.
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ED XRF Qualitative analysis
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Very simple procedure: if one already has a
sample one selects: appropriate excitation
potential (4-50kV), corresponding current
(<2mA) (higher currents Si(Li)-detector
cannot sustain) and counting time (~100sec).
ED XRF Qualitative analysis
Identification of X-ray emission lines
nowadays is fully automated, but no one
should take program results as absolutely
correct. Overlaps, sum peaks and escape
peaks are always present.
 Escape peak (an artefact): With Si(Li)
detectors Si escape peaks occurs 1.74
keV below each 'true' peak.
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Escape Peak in EDS spectrum
Overlaps in
EDS spectrum
Sum peaks
WD XRF Qualitative analysis
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Procedure that requires knowledge.
If one already has a sample one selects:
appropriate diffraction crystal, collimator,
increment with (a fraction of 2Θ), counting time
per increment (~1-2 sec), excitation potential
(~60kV) and corresponding current (~50mA).
The whole qualitative analysis depends on number
of selected diffraction crystals, increment with and
counting time. An average time for qualitative
analysis is usually between 35-45 min (5-10min
per crystal).
WD XRF Qualitative analysis
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Identification of X-ray emission lines
nowadays is fully automated, but no one
should take program results as absolutely
correct. Overlaps and peaks of the X-ray
tube material are usually present in WDS
spectrum.
WD XRF
Qualitative
spectrum
WD XRF
Qualitative
spectrum
light
elements
XRF Quantitative analysis
X-ray fluorescence analysis belongs to a group
of very advanced analytical methods. It
requires wide and profound knowledge
background in chemistry and physics.
 Quantitative analysis its theoretical background
and corresponding calculation steps are the
same for both EDS and WDS analysis.
 But, there are differences between calculation
approaches for corpuscular and photon (Xray) induced X-ray fluorescence.
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XRF Quantitative analysis
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In both cases, corpuscular and photon (X-ray) induced
X-ray fluorescence, there are three important matrix
efects that should be taken in account in the case of
quantitative analysis:
◦ Effect of the atomic number (Z),
◦ Absorption (A), and
◦ Enhanced Fluorescence (F).
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These effect are different when, for example, excitation
is performed with electrons or with X-rays because
electrons and X-rays have different penetration depths
in the „body of sample“ and as a result we have
different effects of ZAF in these two cases.
XRF Quantitative analysis - Effect
of the atomic number (Z)
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Generally speaking, the matrix effects
in X-ray fluorescence analysis result
from the influence of the variations of
chemical compositions of the sample
matrix on the fluorescent intensity of
the wanted element. These effects can
manifest themselves either via a
difference in the absorption of both
the primary and fluorescence
radiations in samples of different
matrix composition (absorption effect)
or via an increase of the radiation
intensity (enhancement effect) due to
the fluorescence radiation of some of
the inter elements. Penetration depth
is also important, higher penetration
depth means more extensive effects of
absorption and fluorescence.
XRF Quantitative analysis –
Absorption (A)
Absorption: Any element can absorb or scatter the
fluorescence of the element of interest.
 This effect occurs when the variations in the matrix
chemical composition result in changes of the mean
absorption coefficients of both the primary radiation of the
source and the fluorescence radiation of the wanted
element.
 The absorption effects occurring in a matrix may either
decrease or increase the intensity of the fluorescence
radiation of the element under determination, depending on
whether the matrix composition changes diminish or
augment the mass absorption coefficient. A strong decrease
of the fluorescence radiation of the wanted element will be
observed if the concentrations of disturbing elements of
slightly lower atomic numbers become larger.
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XRF Quantitative analysis –
Enhanced Florescence (F)
Enhancement: Characteristic x-rays of one element excite
another element in the sample, enhancing its signal.
 This effect involves an extra excitation of the atoms of the
wanted element by the fluorescence radiation of some of
the matrix elements, which in this case become interferents.
 The mechanism of the enhancement effect involves
retransmission of the energy of the primary radiation of the
source in the form of secondary (fluorescence) radiation of
interelements. The energy of this secondary radiation is just
slightly higher than the absorption edge of the wanted
element (Figure VI.3), the latter will be excited more
efficiency than by the primary radiation of the source,
whose energy is higher than that of the secondary radiation
and, consequently, further from the absorption edge.
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Absorption-Enhancement Affects
QUANTITATIVE ANALYSIS
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Calibration-Standard Methods. The analyte-line
intensity from samples is compared with that
from standards having the same form as the
samples and, nearly as possible, the same matrix.
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Internal Standardisation. The calibration-standard
method is improved by quantitative addition to all
samples of an internal standard element having
excitation, absorption and enhancement
characteristics similar to those of the analyte in
the particular matrix. The calibration function
involves measuring the intensity ratio of the
analyte and internal standard lines.
QUANTITATIVE ANALYSIS
“STANDARDLESS ANALYSIS”
Mathematical Corrections. Absorption-enhancement
effects are corrected mathematically by the use of
influence coefficients for each element present (these
are derived experimentally from reference samples).
The basic approach is that the XRF intensity at a
particular wavelength will in some way be affected by
each element in the sample.
 Standardless analysis – the major advantages of X-ray
fluorescence analysis (XRF) – allows fast and easy
determination of the chemical composition without
performing a calibration. Due to powerful matrix
correction based on variable alphas (coefficients for
the correction of matrix effects) every kind of sample
can be analyzed with optimized measurement
parameters for the chemical composition, no matter
which kind of sample preparation has been used.
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Now it is really THE END