High Precision X-Ray Fluorescence Analysis (XRF) by

Chapter 1: Inorganic Analysis
Reference procedure
High Precision X-Ray Fluorescence Analysis (XRF)
by Reconstitution Technique
Keywords
Elemental analysis, reconstitution, precision analysis, synthetic calibration, XRF analysis
Quantities and items tested
Amounts of elements as major and minor constituents (atomic number  12 (magnesium), excluding the noble
gases and halogens) in solid materials such as
metals, oxides and silicates e.g. metal alloys, ores, soils, minerals, cements, building materials
Testing range
Uncertainty of results
Mass fractions of elements from 0.1 g/kg to 800 g/kg
from 5 %
to
0.1 %
Fields of application
Certification of reference materials; precision analysis; e.g. of high-grade inorganic materials such as refractory
metals or special metal alloys
Methodology and instrumentation
The method of reconstitution is based on the use of synthetic calibration samples. Because of the definite
manufacturing process it is possible to use the same sample preparation procedure for both the analysis sample
and for the calibration samples, too.
The basic principle of the reconstitution is – based on a pre-analysis of the analysis sample and „bracketing”
calibration samples – an iterative assimilation of the composition of the calibration samples and the analysis
sample itself. The calibration range is therefore always adjusted to the individual case.
By the iterative adjustment of the composition of the calibration samples and the analysis sample matrix effects
and a deviation from the linear calibration function are avoidable in most cases. The trueness of the method is
controlled by the iterative principle itself.
Because of the advantages of the sample preparation procedure and the high precision XRF-analysis is the ideal
method for realizing the reconstitution principle. The method is basically usable for all analytical methods which
allow an „isoformation“ of calibration and analysis sample, especially all methods based on solutions.
If XRF-analysis is applied the preparation of the calibration samples and the measuring sample of the material to
be investigated is realized by the fusion technique using lithium or sodium tetraborate.
Qualification and quality assurance
A high reliability of the analytical results by using the reconstitution technique is attained by the direct control of
accuracy using the iterative adjustment of calibration and analysis samples resulting in an extensive avoidance of
matrix effects.
If a reconstitution analysis is performed by XRF a number of advantages are contributing to a minimization and a
high reliability of the measuring uncertainty:
 Repeated measurements with identical samples
 Long range time stability of the signals
 Calculable uncertainty contributions by sample preparation procedures
 Optimal control of trueness
 Elimination of matrix effects and optimization of calibration
Contact:
Dr. Markus Ostermann
Phone:
+49 30 8104 1143
E-mail:
[email protected]
Fax:
+49 30 8104 1147
Division 1.4: Process Analytical Technology
Date: Feb. 2014
back to Catalogue
of Reference Procedures
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Reference procedure
Chapter 1: Inorganic Analysis
Further information
Basic principle of the reconstitution technique
In contrast to the conventional „analytical mode“ (calibration for the realization of a correlation between
measuring values and amounts) the contents of elements by using the „synthetic mode“ of reconstitution can
only be accepted as free of interferences and therefore as true, if an identity of analysis sample and the
reference sample is obtained in a sufficient way:
The composition of an unknown analysis sample is determined by synthesis of calibration samples which lead
to “equal signals“ compared to the analysis sample.
The composition of the calibration samples is varied in an iterative way to a point where the difference among the
signals of all samples is no longer significant.
Iterative assimilation of the composition of calibration samples towards the analysis sample
Only pure substances of exactly defined stoichiometry and of well-known grade of impurities are used to prepare
the synthetic calibration samples.
Oxides, carbonates or other compounds of the relevant elements which can be produced in a suitable way with a
high grade of purity are used for this purpose. Also pure elements can be used.
The analysis sample as well as the synthetic mixtures for the calibration samples are prepared as glass fusions
(lithium or sodium tetraborate) to obtain homogeneous samples for the XRF measurements.
While preparing the borate fusions reproducible operating conditions (temperature program) have to be maintained
in order to get an optimum comparability between the calibrations samples and the analysis sample.
1150°C
700°C
850°C
decomposition
warming up
oxidation
(Sodiumnitrate)
cooling down
+ 4.5 g
Lithiumtetraborate
20°C
ca. 70
30
15
15
time in minutes
Temperature program for the fusion of borate glass samples for XRF analysis
Applications
 Analysis of Si-, Ca- und Al-containing alloys
 Analysis of ferrous alloys and nickel alloys
 Analysis of natural and technical oxides
 Analysis of cements and building materials
 Analysis of copper, bronze, brass and white
alloy
 Analysis of ferrochromium
 Analysis of refractory materials (e.g. tungsten,
tantalum, niobium)
Literature
Gotthard Staats und Siegfried Noack,
Qualitätssicherung in der Analytik; Die Rekonstitution – Eine Methode zur Optimierung der Richtigkeit von
Analysen
Verlag Stahleisen GmbH, Düsseldorf 1996
ISBN 3-514-00581-8
Date: Feb. 2014
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