SIST-TP CEN/TR 16176:2012
(Main)Characterization of waste - Screening methods for elemental composition by X-ray fluorescence spectrometry for on-site verification
Characterization of waste - Screening methods for elemental composition by X-ray fluorescence spectrometry for on-site verification
In the framework of the EU Directive 99/31/EC on the landfill of waste and the EU Directive 2000/76/EC on the incineration of waste there is a growing need for fast, easy-to-handle screening tools. In this respect, low costs, fast analyses, control of truck loads and yes/no-acceptance decisions are relevant criteria. The X-ray fluorescence (XRF) technique meets these requirements as a screening tool for on-site verification on the landfill and for entrance control on the incineration plants.
Recent developments of the XRF technology have made this technique a method of choice for on-site analysis, namely miniaturisation of the XRF system (X-ray tube), the optimisation of the calibration programmes and the improvement of the detectors. Therefore, a state-of-the-art document on the current progress of the XRF technology and instruments available for on-site analysis shall support the key arguments, dealing with the pro’s and contra’s, and the performance of these systems to be expected.
The XRF standard EN 15309, is validated for Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, I, Cs, Ba, Ta, W, Hg, Tl, Pb, Bi, Th and U, and describes in the informative annex the procedures for hand-held XRF systems together with the portable/transportable systems (placed in mobile labs). Although XRF can analyse a broad range of elements, the main focus of this document is on the series of elements that is also being covered by EN 15309. Of that series the following elements are related to the landfill directive: As, Ba, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Se, Zn.
The information in this document will be useful in all cases in which on-site determination of the elemental compositions of waste is needed and hand-held instrumentation is therefore used. These cases may include, beside landfills and incineration plant, also waste treatment plants, contaminations soil sites and controls of transports of waste.
Charakterisierung von Abfällen - Anwendung von Screening-Verfahren bei der Vor-Ort-Prüfung - Bestimmung der elementaren Zusammmensetzung mittels Röntgenfluoreszenzspektrometrie
Im Rahmen der EU-Richtlinie 99/31/EG über Abfalldeponien und der EU-Richtlinie 2000/76/EG über die Verbrennung von Abfällen besteht ein wachsender Bedarf an schnellen, leicht zu handhabenden Screening-geräten. In diesem Zusammenhang sind geringe Kosten, schnelle Analysen, Kontrolle von LKW-Ladungen und Ja/Nein-Annahmeentscheide wichtige Kriterien. Die Röntgenfluoreszenztechnik erfüllt diese Anforderungen als Screeninginstrument bei der Vor-Ort-Prüfung auf Deponien und bei der Eingangskontrolle an Verbrennungsanlagen. Jüngste Entwicklungen der RFA-Technologie, insbesondere die Miniaturisierung des RFA-Systems (Röntgenröhre), die Optimierung der Kalibrierungsprogramme und die Verbesserung der Detektoren, haben diese Technik zum Verfahren der Wahl für die Vor-Ort-Analyse gemacht. Deshalb muss ein Dokument zum neusten Stand der Technik, über den aktuellen Fortschritt der für die Vor-Ort-Analyse zur Verfügung stehenden RFA-Technologie und -Geräte, die entscheidenden Argumente, die sich mit den Pros und Kontras und der zu erwartende Leistung dieser Systeme befassen, unterstützen. Die RFA-Norm EN 15309 ist für Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, I, Cs, Ba, Ta, W, Hg, Tl, Pb, Bi, Th und U validiert und im informativen Anhang sind Verfahren für RFA-Handsysteme zusammen mit tragbaren/transportierbaren Systemen (untergebracht in mobilen Laboratorien) beschrieben. Obwohl mit der RFA ein breites Spektrum von Elementen analysiert werden kann, liegt der Schwerpunkt dieses Dokuments auf der Reihe von Elementen, die auch von EN 15309 erfasst werden. Aus dieser Reihe haben folgende Elemente einen Bezug zur Deponierichtlinie: As, Ba, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Se, Zn. Die im vorliegenden Dokument enthaltenen Angaben sind in allen Fällen nützlich, bei denen eine Vor-Ort-Bestimmung der elementaren Zusammensetzung von Abfall benötigt wird und Handgeräte dafür eingesetzt werden. Diese Fälle können neben Deponien und Verbrennungsanlagen auch Abfallbehandlungsanlagen, Standorte mit verunreinigtem Boden (Altlasten) und Kontrollen des Transports von Abfall einschließen.
Caractérisation des déchets - Méthodes de dépistage pour la détermination de la composition élémentaire par spectrométrie à fluorescence de rayons X pour les vérifications in-situ
Karakterizacija odpadkov - Rešetalne metode za elementno sestavo z rentgensko fluorescenčno spektrometrijo na kraju samem
V okviru Direktive Sveta 1999/31/ES o odlaganju odpadkov na odlagališčih in Direktive 000/76/ES Evropskega parlamenta in Sveta o sežiganju odpadkov obstaja rastoča potreba po hitrih rešetalnih orodjih, enostavnih za uporabo. Ustrezna merila v zvezi s tem so nizki stroški, hitre analize, nadzor nad tovori tovornjakov in odločitve o odobritvi, sprejete z odgovorom da/ne. Tehnika rentgenske fluorescence (XRF) kot presejalni test za preverjanje na odlagališču in nadzor pri dostavi v obrat za sežiganje ustreza tem zahtevam. Ta metoda je zaradi nedavnih dosežkov na področju tehnologije rentgenske fluorescence, zlasti zmanjšanja velikosti sistema rentgenske fluorescence (rentgenske cevi), optimizacije programov za kalibracijo in izboljšanja detektorja, najprimernejša za analizo na kraju samem. Zato mora dokument stanja tehnike o sedanjem napredku na področju tehnologije in instrumentov za rentgensko fluorescenco, ki so na voljo za analizo na kraju samem, utemeljiti ključne argumente, pri čemer morajo biti navedene dobre in slabe strani, in oceniti pričakovano zmogljivost teh sistemov. Standard za rentgensko fluorescenco EN 15309 je potrjen za Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, I, Cs, Ba, Ta, W, Hg, Tl, Pb, Bi, Th in U ter v informativnem dodatku opisuje postopke za ročne sisteme za rentgensko fluorescenco in prenosne/prevozne sisteme (nameščene v mobilnih laboratorijih). Čeprav se z rentgensko fluorescenco lahko analizirajo številni elementi, se ta standard osredotoča na serijo elementov, ki jih zajema tudi EN 15309. Med elementi iz te serije so z direktivo o odpadkih povezani: As, Ba, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Se, Zn. Informacije iz tega dokumenta so uporabne za vse primere, ko je treba določiti elementarno sestavo odpadkov in zato se uporabijo ročni instrumenti. Ti primeri lahko poleg odlagališč in obratov za sežiganje vključujejo tudi obrate za obdelavo odpadkov, območja s kontaminirano zemljino in nadzor prevoza odpadkov.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CEN/TR 16176:2012
01-februar-2012
.DUDNWHUL]DFLMDRGSDGNRY5HãHWDOQHPHWRGH]DHOHPHQWQRVHVWDYR]UHQWJHQVNR
IOXRUHVFHQþQRVSHNWURPHWULMRQDNUDMXVDPHP
Characterization of waste - Screening methods for elemental composition by X-ray
fluorescence spectrometry for on-site verification
Charakterisierung von Abfällen - Anwendung von Screening-Verfahren bei der Vor-Ort-
Prüfung - Bestimmung der elementaren Zusammmensetzung mittels
Röntgenfluoreszenzspektrometrie
Caractérisation des déchets - Méthodes de dépistage pour la détermination de la
composition élémentaire par spectrométrie à fluorescence de rayons X pour les
vérifications in-situ
Ta slovenski standard je istoveten z: CEN/TR 16176:2011
ICS:
13.030.01 Odpadki na splošno Wastes in general
SIST-TP CEN/TR 16176:2012 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CEN/TR 16176:2012
TECHNICAL REPORT
CEN/TR 16176
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
November 2011
ICS 13.030.01
English Version
Characterization of waste - Screening methods for elemental
composition by X-ray fluorescence spectrometry for on-site
verification
Caractérisation des déchets - Méthodes de dépistage pour Charakterisierung von Abfällen - Anwendung von
la détermination de la composition élémentaire par Screening-Verfahren bei der Vor-Ort-Prüfung - Bestimmung
spectrométrie à fluorescence de rayons X pour les der elementaren Zusammmensetzung mittels
vérifications in situ Röntgenfluoreszenzspektrometrie
This Technical Report was approved by CEN on 3 October 2011. It has been drawn up by the Technical Committee CEN/TC 292.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16176:2011: E
worldwide for CEN national Members.
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Contents Page
Foreword .3
Introduction .4
1 Purpose .5
2 Description of the XRF technique .5
2.1 General .5
2.2 Principle of XRF .5
2.3 Interferences .6
2.4 Measurement .7
2.5 Calibration/evaluation .7
2.6 Validation .8
3 Overview XRF applications .9
4 Influence of the sample preparation on the result .9
5 Evaluation of the XRF screening technique . 13
6 Robustness study: description and results . 15
6.1 General . 15
6.2 Technical description of the instruments . 15
6.3 Description of the selected samples and their characterisation . 16
6.4 Results of the field trial . 17
6.4.1 Defining performance criteria . 17
6.4.2 Evaluation of the repeatability, reproducibility and accuracy . 18
6.4.3 Influence of the sample pretreatment . 19
6.4.4 Evaluation of false positive / false negative results. 22
6.4.5 Limit of detection . 22
6.4.6 General evaluation of the portable XRF instruments. 22
6.4.7 Conclusions of the robustness study . 22
7 Conclusions . 23
Annex A (informative) Pre-normative robustness study . 24
Annex B (informative) Summary of EPA report on XRF technologies for measuring trace elements
in soil and sediment . 38
Bibliography . 42
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Foreword
This document (CEN/TR 16176:2011) has been prepared by Technical Committee CEN/TC 292
“Characterization of Waste”, the secretariat of which is held by NEN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
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Introduction
Although bench-top instruments generally provide much more conclusive results, hand-held XRF instruments
are becoming an interesting screening tool for a wide range of applications. Their portability and their ability to
identify, characterise and also analyse a wide range of elements rapidly, along with the fact that little technical
expertise is needed to operate them, make the hand-held XRF instruments very useful. The recent
developments in the XRF technology tends to create hand-held instruments with performance levels
approaching bench top equipment. Some years ago, hand-held instruments required the use of radioactive
materials to provide a source of X-rays, resulting in very stringent regulatory demands. The development of
miniaturised low-power X-ray tubes overcomes these problems and provides new opportunities for the hand-
held instruments. Recent advances in the improvement of the detector efficiency led to a significant decrease
in the detection limits for hand-held systems compared to the older ones. Due to the required compact
configuration for hand-held XRF systems only energy dispersive X-ray fluorescence (EDXRF) are on the
market. On the other hand wavelength dispersive XRFs (WDXRF) are generally more laborious.
The use of the XRF technique in field screening trials can provide a number of benefits compared to the
traditional laboratory techniques. On-site analyses ensure a fast turnaround between the measurement itself
and the availability of data results. Sample preparation is frequently unnecessary or will be limited. Screening
can gain a large sample data set on a short time frame, but that can be at the expense of the accuracy and
precision. When better accuracy is required confirmative analysis has to be performed. This approach will
surely result in a significant reduction of analysis time and costs.
This report focuses on hand-held XRF instruments, although portable bench-top instruments are also on the
market for this type of application. Whenever portable instruments are specifically addressed in this report,
both types of instruments can be considered.
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1 Purpose
In the framework of the EU Directive 99/31/EC on the landfill of waste and the EU Directive 2000/76/EC on the
incineration of waste there is a growing need for fast, easy-to-handle screening tools. In this respect, low
costs, fast analyses, control of truck loads and yes/no-acceptance decisions are relevant criteria. The X-ray
fluorescence (XRF) technique meets these requirements as a screening tool for on-site verification on the
landfill and for entrance control on the incineration plants.
Recent developments of the XRF technology have made this technique a method of choice for on-site
analysis, namely miniaturisation of the XRF system (X-ray tube), the optimisation of the calibration
programmes and the improvement of the detectors. Therefore, a state-of-the-art document on the current
progress of the XRF technology and instruments available for on-site analysis shall support the key
arguments, dealing with the pro‟s and contra‟s, and the performance of these systems to be expected.
The XRF standard EN 15309, is validated for Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,
As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, I, Cs, Ba, Ta, W, Hg, Tl, Pb, Bi, Th and U, and
describes in the informative annex the procedures for hand-held XRF systems together with the
portable/transportable systems (placed in mobile labs). Although XRF can analyse a broad range of elements,
the main focus of this document is on the series of elements that is also being covered by EN 15309. Of that
series the following elements are related to the landfill directive: As, Ba, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Se,
Zn.
The information in this document will be useful in all cases in which on-site determination of the elemental
compositions of waste is needed and hand-held instrumentation is therefore used. These cases may include,
beside landfills and incineration plant, also waste treatment plants, contaminations soil sites and controls of
transports of waste.
2 Description of the XRF technique
2.1 General
X-ray fluorescence spectrometry is a fast and reliable method for the analysis of the total content of certain
elements within different matrices. The quality of the results obtained depends very closely on the type of
instrument used, e.g. hand-held, bench top. When selecting a specific instrument several factors have to be
considered, such as the matrices to be analysed, elements to be determined, detection limits required and the
measuring time. The quality of the results depends on the element to be determined and on the surrounding
matrix, together with the applied sample preparation method, and the heterogeneity of the test sample.
2.2 Principle of XRF
An electron can be ejected from its atomic orbital by the absorption of a light wave (photon) of sufficient
energy [1]. The energy of the photon (h ) must be greater than the energy with which the electron is bound to
the nucleus of the atom. When an inner orbital electron is ejected from an atom, an electron from a higher
energy level orbital will be transferred to the lower energy level orbital. During this transition a photon maybe
emitted from the atom. This fluorescent light is called the characteristic X-ray of the element (Figure 1). The
energy of the emitted photon will be equal to the difference in energies between the two orbitals occupied by
the electron making the transition. Because the energy difference between two specific orbital shells, in a
given element, is always the same (i.e. characteristic of a particular element), the photon emitted when an
electron moves between these two levels, will always have the same energy. Therefore, by determining the
energy (wavelength) of the X-rays (photon) emitted by a particular element, it is possible to determine the
identity of that element.
For a particular energy (wavelength) of fluorescent light emitted by an element, the number of photons per unit
time (generally referred to as peak intensity or count rate) is related to the amount of that analyte in the
sample. The counting rates for all detectable elements within a sample are usually calculated by counting, for
a set amount of time, the number of photons that are detected for the various analytes‟ characteristic X-ray
energy lines. It is important to note that these fluorescent lines are actually observed as peaks with a
semi-Gaussian distribution depending on the resolution of modern detector technology. Therefore, by
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determining the energy of the X-ray peaks in a sample‟s spectrum, and by calculating the count rate of the
various elemental peaks, it is possible to qualitatively establish the elemental composition of the samples and
to quantitatively measure the concentration of these elements.
Key
A excitation: X-rays from X-ray source
B fluorescence: Characteristic X-ray
Figure 1 — Principle of XRF
The basic configuration of an EDXRF system consists of an excitation source and a detector, coupled to data
processing unit, as shown in Figure 2.
Key
A X-ray source
B detector
Figure 2 — Basic configuration of an XRF system
2.3 Interferences
Interferences in X-ray fluorescence spectrometry are due to spectral line overlaps, matrix effects, spectral
artefacts and particle size or mineralogical effects.
Spectral line overlaps occur when an analytical line cannot be resolved from the line of a different element.
Corrections for these interferences are made using the algorithms provided with the software.
Matrix effects occur when the X-ray fluorescence radiation from the analyte element is absorbed or enhanced
by other elements in the sample before it reaches the detector. In the case of complex matrices these effects
generally have to be corrected.
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Spectral artefacts e.g. escape peaks, sum peaks, pulse pile up lines, dead time, Bremsstrahlung correction,
are accounted for by the provided software. Spectral artefacts differ for energy dispersive and wavelength
dispersive XRF spectrometry.
Particle size effects can be reduced by milling the sample, and both particle size and mineralogical effects can
be eliminated by preparing bead samples. It is vital for quantitative analysis that the same sample preparation
procedure is applied to both the standards and the samples to be analysed.
2.4 Measurement
All X-ray spectrometers are supplied with a spectrometer software programme to operate the instrument. The
software packages are manufacturer depended and contain two major modules:
analytical measurement programme for data collection. This module controls the measurement of a
sample using a certain set of measurement parameters e.g. tube setting (kV, mA), targets and crystals,
detectors, measurement times. The analytical programme is always linked to a selected evaluation and
calibration programme. Actually, the same measurement conditions have to be applied for both the
standards of the calibration curve and the samples. Because in screening analysis the measurements will
be performed with the predefined analytical programmes, no further detailed descriptions will be given of
the analytical measurement parameters. Follow the manufacturer‟s instruction for further operation and
handling of the analytical software package;
evaluation programme for data processing. This module converts the measured intensities of the different
element lines to elemental concentrations taking all corrections into account. There are various types of
evaluation programmes available and each manufacturer has set up his own programmes for data
processing based on the XRF principles.
Sensitivity, instrumental detection limits and precision are instrument dependent and should therefore be
investigated and established for each individual analyte line on that particular instrument, and, if relevant, as a
function of matrix type and sample preparation procedure.
The XRF systems (hand-held as well as bench top) for screening purposes are all provided with precalibrated
measurement programmes, setup by the manufacturer, and therefore the user does not need to calibrate the
system itself. The user may be able to calibrate the XRF system itself, but it is not a requirement. It should be
stressed out that the user needs to verify the calibration programme using reference samples in order to gain
insights in the expected accuracy and precision of the XRF calibration programme. More information about the
validation will be described in 2.6.
2.5 Calibration/evaluation
For calibration purposes the measurement of analyte lines of samples of known composition is needed. The
basic equation implies a linear relationship between the intensity and the concentration.
c a a I (1)
i i,0 i,1 i
where
c is the concentration of the element of interest, expressed as mg/kg or percentage dry matter;
i
a is the offset of the calibration curve;
i,0
a is the slope of the calibration curve;
i,1
I is the net intensity of the element of interest, expressed as counts per second.
i
Matrix effects have to be taken into account in X-ray spectrometry according to the following equation:
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c (a a I ) M (2)
i i,0 i,1 i
where
M is the correction term due to the matrix effects.
Different procedures for correcting matrix effects may be used according to the analytical accuracy required:
the scattered radiation method is based on the principle that the intensities of the analyte line and of the
Compton line are affected in the same proportion due to the overall mass absorption coefficient of the
sample. This linear relationship holds when all analytes are at low concentrations (trace elements) and
their absorption coefficients are not affected by an adjacent absorption edge. In this case an internal
Compton correction can be used. Beside that, a correction method using the Compton intensity with mass
absorption coefficients (MAC) is also applicable. In this method, the intensities of the major elements are
measured to apply a jump edge correction for the analysed trace elements;
correction using the fundamental parameter approach;
correction using theoretical correction coefficients (alphas) taking basic physical principles, instrumental
geometry etc. into account;
correction using empirical correction coefficients (alphas) based on regression analysis of standards with
known elemental concentrations.
For more information about the various calibration procedures is referred to EN 15309.
2.6 Validation
Prior to analysis of a sample, the available pre-calibrated analytical method has to be validated. The validation
can be performed on different levels. First of all, and this is also a requirement when performing screening
analysis, a verification of the calibration programme using a reference material with known composition has to
be carried out on a regular base in order to follow-up the stability and drift of the system. Secondly, control
analyses can be performed by using reference samples with a similar composition as the samples under
investigation to gain insights in the expected measurement uncertainty. If no reference materials with a
comparable matrix are available, only a qualitative analysis with indicative concentration values can be
performed.
The reference sample can consist of:
in-house or commercially available reference materials - if possible certified - with matrices similar to that
of the sample;
synthetic samples, made by weighing the appropriate amount of each pure reagent;
site specific or batch specific samples, similar to the matrix of the sample;
standard addition method or spiked samples may also be used to create standards for which appropriate
reference materials are not available for an element of interest. The matrix material needs to match that
of the sample.
The element concentrations of the reference samples have to be known by certification or by determination
with a different analytical technique.
The reference samples have to be analysed under the same analytical conditions as the sample, meaning the
same sample preparation (pellet, powder etc.), the same analytical measurement method etc.
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3 Overview XRF applications
An overview of „portable/benchtop‟ and „hand-held‟ instruments that are at present commercially available, is
given in Annex A. The „hand-held‟ instruments are generally less than 2 kg in weight, whereas the
„portable/benchtop‟ instruments are not below 9 kg.
Waste samples can consist of different matrix types, each of them may require an appropriate sample
preparation. See Annex B in EN 15309, where five different types are described: 1. soil, sediment, fly ash and
sludge samples, 2. samples consisting of carbon matrices, 3. liquid samples, 4. paste-like materials, 5. scrap
samples. The procedures of the different sample preparation techniques are described in ISO 11464,
EN 15002.
Application of XRF in „on-site‟ verification at the entrance of landfill or a waste incinerator, will usually consist
of the check of the presence of one or more components in solid material, with relatively low carbon content.
For large landfills en plants, limited laboratory facilities will be present for sample preparation and
„portable/benchtop‟ instruments available.
Application of XRF during transport in traffic, will require a hand-held instruments at different sizes and forms
of load must be approached.
Applications of XRF ‟in the field‟, e.g. looking for hot spots in suspected areas; hand-held instruments are
preferred because of their mobility.
4 Influence of the sample preparation on the result
Although the XRF technique is a non-destructive technique and it is often stated that no or only a limited
sample preparation is required, the applied sample preparation method plays an important role in the final
quality of the obtained results. The moisture content and the particle size of a solid sample have a significant
influence on the obtained quality of the results. The highest quality can be obtained when the samples are
dried and finely ground. However, on the field it is not always possible to perform an extended sample
pretreatment.
XRF analysis can be performed on samples with different levels of pretreatment resulting in different quality of
result:
In situ analysis: The XRF is placed directly onto the sample and the analysis is performed without any
sample preparation (Figure 3). A limited handling of the sample (flattening, make it more compact) can
improve the quality of the obtained results. Nevertheless, the obtained results will only be qualitative and
can only be considered as indicative.
Figure 3 — In situ analysis
Analysis of a bagged sample: A simple way of improving the quality of the XRF results can be achieved
by homogenisation of the sample. When putting the sample in a plastic bag, the sample can be
homogenised roughly and crushed into smaller parts by hand. The XRF measurement can be performed
directly on the bagged sample (Figure 4).
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Figure 4 — Analysis of a bagged sample
Analysis of a wet sieved sample: Although a wet sample is not easy to sieve, it can significantly improve
the XRF data quality. The sieved sample can be put in a bag and analysed as such or it can be placed in
a sample cup and analysed with the XRF in stand mode (Figure 5). Using this procedure the XRF results
can be considered as semi-quantitative.
Figure 5 — Analysis of a wet sieved sample
Analysis of a dried and ground sample: If a mobile lab is present at the site under investigation, it can be
equipped with a drying oven (e.g. microwave) and grinding tools. Analysing a dried and finely ground
sample will significantly improve the accuracy and precision of the XRF results. The prepared sample can
be analysed with the XRF in stand mode (Figure 6). Using this procedure, one have to keep in mind that
longer testing times are required and that the sample throughput will be lower compared to the direct XRF
analysis.
Figure 6 — Analysis of a dried and ground sample
In a publication of Vanhoof et al [2] several types of XRF instruments were compared, together with the
influence of the applied preparation method on the acquired data using a field portable instrument. The
influence of the pretreatment on the acquired data is shown in Figure 7. Performing in situ analysis with the
2
field portable Spectrace 9000 resulted in low regression coefficients R of 0,7 for both elements. Also the
slopes were very low, therefore, the XRF values with a low concentration level were overestimated while the
higher levels were underestimated. A limited homogenisation (sieving over 2 mm) of the soil sample
significantly improved the regression parameters resulting in more comparable results.
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Figure 7 — Method comparison for the elements Zn and Pb, measured with the field portable EDXRF,
as a function of the pretreatment
These results confirm that in situ analyses are strongly influenced by the heterogeneity of the samples. A
limitation of the in situ analysis, without any homogenisation, is that only the surface top layer is analysed on
2
just a small soil area (± 5 cm ) corresponding to the XRF measuring window. Furthermore, the
homogenisation process also assure that the same sample will be analyzed by the XRF system and the
reference ICP-AES technique, while in situ analysis can be regarded as a one point surface analysis.
11
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Field analysis are particularly suitable to define „hot spots‟ and to differentiate contaminated areas giving a
measure of the degree of contamination. For these purposes the sample strategy is of major concern to obtain
useful results. Further pretreatment i.e. drying and fine grounding of the soil sample, still improve the data
quality but less significant. However, the largest progress in achieving comparable data between the XRF and
the ICP-AES system is obtained when a minimal homogenisation is performed.
In commission of the RWS Waterdienst (The Netherlands) a similar study was performed by N. Walraven [3]
to evaluate the possibilities of XRF in order to measure Pb, Cu, Zn, As, Cd , Hg, Ni, Cr, Mo, Ba, Sn, V and Se
in sediments. The performance characteristics of the portable Niton XL3t 600 XRF analyser were determined
for the analysis of sediments, and special attention was spent to the evaluation of field moisture samples.
Using certified reference materials the accuracy of the XRF system was determined. In the project two
different hand-held Niton XRF systems were used (same type). Based on the results shown in Table 1, it can
be stated that different performance characteristics were obtained with the same type of XRF instruments.
Nevertheless it is possible to improve the calibration programme to obtain more accurate results. These data
confirm that it is a necessity to validate always the XRF instrument in use.
Table 1 — Yield determined on certified reference materials
Yield Zn Pb Cu As Cr Ba Ni Sn Hg Cd V Mo
% % % % % % % % % % % %
84 to 89 to 73 to 101 to 57 to 90 to 96 to 79 to 104 to 84 to 74 to
XRF 1 ND
89 100 107 112 86 132 137 86 155 108 79
78 to 79 to 69 to 54 to 47 to 77 to 80 to 111 to 85 to 144
...
SLOVENSKI STANDARD
kSIST-TP FprCEN/TR 16176:2011
01-julij-2011
.DUDNWHUL]DFLMDRGSDGNRY5HãHWDOQHPHWRGH]DHOHPHQWQRVHVWDYR]UHQWJHQVNR
IOXRUHVFHQþQRVSHNWURPHWULMRQDNUDMXVDPHP
Characterization of waste - Screening methods for elemental composition by X-ray
fluorescence spectrometry for on-site verification
Charakterisierung von Abfällen - Anwendung von Screening-Verfahren bei der Vor-Ort-
Prüfung - Bestimmung der elementaren Zusammmensetzung mittels
Röntgenfluoreszenzspektrometrie
Méthodes de dépistage pour la détermination de la composition élémentaire par
spectrométrie à fluorescence de rayons X pour les vérifications in-situ
Ta slovenski standard je istoveten z: FprCEN/TR 16176
ICS:
13.030.01 Odpadki na splošno Wastes in general
kSIST-TP FprCEN/TR 16176:2011 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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kSIST-TP FprCEN/TR 16176:2011
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kSIST-TP FprCEN/TR 16176:2011
TECHNICAL REPORT
FINAL DRAFT
FprCEN/TR 16176
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
June 2011
ICS 13.030.01
English Version
Characterization of waste - Screening methods for elemental
composition by X-ray fluorescence spectrometry for on-site
verification
Caractérisation des déchets - Méthodes de dépistage pour Charakterisierung von Abfällen - Anwendung von
la détermination de la composition élémentaire par Screening-Verfahren bei der Vor-Ort-Prüfung - Bestimmung
spectrométrie à fluorescence de rayons X pour les der elementaren Zusammmensetzung mittels
vérifications in-situ Röntgenfluoreszenzspektrometrie
This draft Technical Report is submitted to CEN members for Technical Committee Approval. It has been drawn up by the Technical
Committee CEN/TC 292.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to
provide supporting documentation.
Warning : This document is not a Technical Report. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a Technical Report.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. FprCEN/TR 16176:2011: E
worldwide for CEN national Members.
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Contents Page
Foreword .3
Introduction .4
1 Purpose .5
2 Description of the XRF technique .5
2.1 General .5
2.2 Principle of XRF .5
2.3 Interferences .6
2.4 Measurement .7
2.5 Calibration/evaluation .7
2.6 Validation .8
3 Overview XRF applications .9
4 Influence of the sample preparation on the result .9
5 Evaluation of the XRF screening technique . 13
6 Robustness study: description and results . 15
6.1 General . 15
6.2 Technical description of the instruments . 15
6.3 Description of the selected samples and their characterisation . 16
6.4 Results of the field trial . 17
6.4.1 Defining performance criteria . 17
6.4.2 Evaluation of the repeatability, reproducibility and accuracy . 19
6.4.3 Influence of the sample pretreatment . 19
6.4.4 Evaluation of false positive / false negative results. 22
6.4.5 Limit of detection . 22
6.4.6 General evaluation of the portable XRF instruments. 22
6.4.7 Conclusions of the robustness study . 22
7 Conclusions . 23
Annex A (informative) Pre-normative robustness study . 24
Annex B (informative) Summary of EPA report on XRF technologies for measuring trace elements
in soil and sediment . 38
Bibliography . 42
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Foreword
This document (FprCEN/TR 16176:2011) has been prepared by Technical Committee CEN/TC 292
“Characterization of Waste”, the secretariat of which is held by NEN.
This document is currently submitted to the Technical Committee Approval.
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Introduction
Although bench-top instruments generally provide much more conclusive results, hand-held XRF instruments
are becoming an interesting screening tool for a wide range of applications. Their portability and their ability to
identify, characterise and also analyse a wide range of elements rapidly, along with the fact that little technical
expertise is needed to operate them, make the hand-held XRF instruments very useful. The recent
developments in the XRF technology tends to create hand-held instruments with performance levels
approaching bench top equipment. Some years ago, hand-held instruments required the use of radioactive
materials to provide a source of X-rays, resulting in very stringent regulatory demands. The development of
miniaturised low-power X-ray tubes overcomes these problems and provides new opportunities for the hand-
held instruments. Recent advances in the improvement of the detector efficiency led to a significant decrease
in the detection limits for hand-held systems compared to the older ones. Due to the required compact
configuration for hand-held XRF systems only energy dispersive X-ray fluorescence (EDXRF) are on the
market. On the other hand wavelength dispersive XRFs (WDXRF) are generally more laborious.
The use of the XRF technique in field screening trials can provide a number of benefits compared to the
traditional laboratory techniques. On-site analyses ensure a fast turnaround between the measurement itself
and the availability of data results. Sample preparation is frequently unnecessary or will be limited. Screening
can gain a large sample data set on a short time frame, but that can be at the expense of the accuracy and
precision. When better accuracy is required confirmative analysis has to be performed. This approach will
surely result in a significant reduction of analysis time and costs.
This report focuses on hand-held XRF instruments, although portable bench-top instruments are also on the
market for this type of application. Whenever portable instruments are specifically addressed in this report,
both types of instruments can be considered.
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1 Purpose
In the framework of the EU Directive 99/31/EC on the landfill of waste and the EU Directive 2000/76/EC on the
incineration of waste there is a growing need for fast, easy-to-handle screening tools. In this respect, low
costs, fast analyses, control of truck loads and yes/no-acceptance decisions are relevant criteria. The X-ray
fluorescence (XRF) technique meets these requirements as a screening tool for on-site verification on the
landfill and for entrance control on the incineration plants.
Recent developments of the XRF technology have made this technique a method of choice for on-site
analysis, namely miniaturisation of the XRF system (X-ray tube), the optimisation of the calibration
programmes and the improvement of the detectors. Therefore, a state-of-the-art document on the current
progress of the XRF technology and instruments available for on-site analysis shall support the key
arguments, dealing with the pro’s and contra’s, and the performance of these systems to be expected.
The XRF standard EN 15309, is validated for Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,
As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, I, Cs, Ba, Ta, W, Hg, Tl, Pb, Bi, Th and U, and
describes in the informative annex the procedures for hand-held XRF systems together with the
portable/transportable systems (placed in mobile labs). Although XRF can analyse a broad range of elements,
the main focus of this document is on the series of elements that is also being covered by EN 15309. Of that
series the following elements are related to the landfill directive: As, Ba, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Se,
Zn.
The information in this document will be useful in all cases in which on-site determination of the elemental
compositions of waste is needed and hand-held instrumentation is therefore used. These cases may include,
beside landfills and incineration plant, also waste treatment plants, contaminations soil sites and controls of
transports of waste.
2 Description of the XRF technique
2.1 General
X-ray fluorescence spectrometry is a fast and reliable method for the analysis of the total content of certain
elements within different matrices. The quality of the results obtained depends very closely on the type of
instrument used, e.g. hand-held, bench top. When selecting a specific instrument several factors have to be
considered, such as the matrices to be analysed, elements to be determined, detection limits required and the
measuring time. The quality of the results depends on the element to be determined and on the surrounding
matrix, together with the applied sample preparation method, and the heterogeneity of the test sample.
2.2 Principle of XRF
An electron can be ejected from its atomic orbital by the absorption of a light wave (photon) of sufficient
energy [1]. The energy of the photon (hν) must be greater than the energy with which the electron is bound to
the nucleus of the atom. When an inner orbital electron is ejected from an atom, an electron from a higher
energy level orbital will be transferred to the lower energy level orbital. During this transition a photon maybe
emitted from the atom. This fluorescent light is called the characteristic X-ray of the element (Figure 1). The
energy of the emitted photon will be equal to the difference in energies between the two orbitals occupied by
the electron making the transition. Because the energy difference between two specific orbital shells, in a
given element, is always the same (i.e. characteristic of a particular element), the photon emitted when an
electron moves between these two levels, will always have the same energy. Therefore, by determining the
energy (wavelength) of the X-rays (photon) emitted by a particular element, it is possible to determine the
identity of that element.
For a particular energy (wavelength) of fluorescent light emitted by an element, the number of photons per unit
time (generally referred to as peak intensity or count rate) is related to the amount of that analyte in the
sample. The counting rates for all detectable elements within a sample are usually calculated by counting, for
a set amount of time, the number of photons that are detected for the various analytes’ characteristic X-ray
energy lines. It is important to note that these fluorescent lines are actually observed as peaks with a
semi-Gaussian distribution depending on the resolution of modern detector technology. Therefore, by
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determining the energy of the X-ray peaks in a sample’s spectrum, and by calculating the count rate of the
various elemental peaks, it is possible to qualitatively establish the elemental composition of the samples and
to quantitatively measure the concentration of these elements.
Key
A excitation: X-rays from X-ray source
B fluorescence: Characteristic X-ray
Figure 1 — Principle of XRF
The basic configuration of an EDXRF system consists of an excitation source and a detector, coupled to data
processing unit, as shown in Figure 2.
Key
A X-ray source
B detector
Figure 2 — Basic configuration of an XRF system
2.3 Interferences
Interferences in X-ray fluorescence spectrometry are due to spectral line overlaps, matrix effects, spectral
artefacts and particle size or mineralogical effects.
Spectral line overlaps occur when an analytical line cannot be resolved from the line of a different element.
Corrections for these interferences are made using the algorithms provided with the software.
Matrix effects occur when the X-ray fluorescence radiation from the analyte element is absorbed or enhanced
by other elements in the sample before it reaches the detector. In the case of complex matrices these effects
generally have to be corrected.
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Spectral artefacts e.g. escape peaks, sum peaks, pulse pile up lines, dead time, Bremsstrahlung correction,
are accounted for by the provided software. Spectral artefacts differ for energy dispersive and wavelength
dispersive XRF spectrometry.
Particle size effects can be reduced by milling the sample, and both particle size and mineralogical effects can
be eliminated by preparing bead samples. It is vital for quantitative analysis that the same sample preparation
procedure is applied to both the standards and the samples to be analysed.
2.4 Measurement
All X-ray spectrometers are supplied with a spectrometer software programme to operate the instrument. The
software packages are manufacturer depended and contain two major modules:
analytical measurement programme for data collection. This module controls the measurement of a
sample using a certain set of measurement parameters e.g. tube setting (kV, mA), targets and crystals,
detectors, measurement times. The analytical programme is always linked to a selected evaluation and
calibration programme. Actually, the same measurement conditions have to be applied for both the
standards of the calibration curve and the samples. Because in screening analysis the measurements will
be performed with the predefined analytical programmes, no further detailed descriptions will be given of
the analytical measurement parameters. Follow the manufacturer’s instruction for further operation and
handling of the analytical software package;
evaluation programme for data processing. This module converts the measured intensities of the different
element lines to elemental concentrations taking all corrections into account. There are various types of
evaluation programmes available and each manufacturer has set up his own programmes for data
processing based on the XRF principles.
Sensitivity, instrumental detection limits and precision are instrument dependent and should therefore be
investigated and established for each individual analyte line on that particular instrument, and, if relevant, as a
function of matrix type and sample preparation procedure.
The XRF systems (hand-held as well as bench top) for screening purposes are all provided with precalibrated
measurement programmes, setup by the manufacturer, and therefore the user does not need to calibrate the
system itself. The user may be able to calibrate the XRF system itself, but it is not a requirement. It should be
stressed out that the user needs to verify the calibration programme using reference samples in order to gain
insights in the expected accuracy and precision of the XRF calibration programme. More information about the
validation will be described in 2.6.
2.5 Calibration/evaluation
For calibration purposes the measurement of analyte lines of samples of known composition is needed. The
basic equation implies a linear relationship between the intensity and the concentration.
c =a +a ×I (1)
i i,0 i,1 i
where
c is the concentration of the element of interest, expressed as mg/kg or percentage dry matter;
i
a is the offset of the calibration curve;
i,0
a is the slope of the calibration curve;
i,1
I is the net intensity of the element of interest, expressed as counts per second.
i
Matrix effects have to be taken into account in X-ray spectrometry according to the following equation:
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c = (a +a ×I )×M (2)
i i,0 i,1 i
where
M is the correction term due to the matrix effects.
Different procedures for correcting matrix effects may be used according to the analytical accuracy required:
the scattered radiation method is based on the principle that the intensities of the analyte line and of the
Compton line are affected in the same proportion due to the overall mass absorption coefficient of the
sample. This linear relationship holds when all analytes are at low concentrations (trace elements) and
their absorption coefficients are not affected by an adjacent absorption edge. In this case an internal
Compton correction can be used. Beside that, a correction method using the Compton intensity with mass
absorption coefficients (MAC) is also applicable. In this method, the intensities of the major elements are
measured to apply a jump edge correction for the analysed trace elements;
correction using the fundamental parameter approach;
correction using theoretical correction coefficients (alphas) taking basic physical principles, instrumental
geometry etc. into account;
correction using empirical correction coefficients (alphas) based on regression analysis of standards with
known elemental concentrations.
For more information about the various calibration procedures is referred to EN 15309.
2.6 Validation
Prior to analysis of a sample, the available pre-calibrated analytical method has to be validated. The validation
can be performed on different levels. First of all, and this is also a requirement when performing screening
analysis, a verification of the calibration programme using a reference material with known composition has to
be carried out on a regular base in order to follow-up the stability and drift of the system. Secondly, control
analyses can be performed by using reference samples with a similar composition as the samples under
investigation to gain insights in the expected measurement uncertainty. If no reference materials with a
comparable matrix are available, only a qualitative analysis with indicative concentration values can be
performed.
The reference sample can consist of:
in-house or commercially available reference materials - if possible certified - with matrices similar to that
of the sample;
synthetic samples, made by weighing the appropriate amount of each pure reagent;
site specific or batch specific samples, similar to the matrix of the sample;
standard addition method or spiked samples may also be used to create standards for which appropriate
reference materials are not available for an element of interest. The matrix material needs to match that
of the sample.
The element concentrations of the reference samples have to be known by certification or by determination
with a different analytical technique.
The reference samples have to be analysed under the same analytical conditions as the sample, meaning the
same sample preparation (pellet, powder etc.), the same analytical measurement method etc.
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3 Overview XRF applications
An overview of ‘portable/benchtop’ and ‘hand-held’ instruments that are at present commercially available, is
given in Annex A. The ‘hand-held’ instruments are generally less than 2 kg in weight, whereas the
‘portable/benchtop’ instruments are not below 9 kg.
Waste samples can consist of different matrix types, each of them may require an appropriate sample
preparation. See Annex B in EN 15309, where five different types are described: 1. soil, sediment, fly ash and
sludge samples, 2. samples consisting of carbon matrices, 3. liquid samples, 4. paste-like materials, 5. scrap
samples. The procedures of the different sample preparation techniques are described in ISO 11464,
EN 15002.
Application of XRF in ‘on-site’ verification at the entrance of landfill or a waste incinerator, will usually consist
of the check of the presence of one or more components in solid material, with relatively low carbon content.
For large landfills en plants, limited laboratory facilities will be present for sample preparation and
‘portable/benchtop’ instruments available.
Application of XRF during transport in traffic, will require a hand-held instruments at different sizes and forms
of load must be approached.
Applications of XRF ’in the field’, e.g. looking for hot spots in suspected areas; hand-held instruments are
preferred because of their mobility.
4 Influence of the sample preparation on the result
Although the XRF technique is a non-destructive technique and it is often stated that no or only a limited
sample preparation is required, the applied sample preparation method plays an important role in the final
quality of the obtained results. The moisture content and the particle size of a solid sample have a significant
influence on the obtained quality of the results. The highest quality can be obtained when the samples are
dried and finely ground. However, on the field it is not always possible to perform an extended sample
pretreatment.
XRF analysis can be performed on samples with different levels of pretreatment resulting in different quality of
result:
In situ analysis: The XRF is placed directly onto the sample and the analysis is performed without any
sample preparation (Figure 3). A limited handling of the sample (flattening, make it more compact) can
improve the quality of the obtained results. Nevertheless, the obtained results will only be qualitative and
can only be considered as indicative.
Figure 3 — In situ analysis
Analysis of a bagged sample: A simple way of improving the quality of the XRF results can be achieved
by homogenisation of the sample. When putting the sample in a plastic bag, the sample can be
homogenised roughly and crushed into smaller parts by hand. The XRF measurement can be performed
directly on the bagged sample (Figure 4).
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Figure 4 — Analysis of a bagged sample
Analysis of a wet sieved sample: Although a wet sample is not easy to sieve, it can significantly improve
the XRF data quality. The sieved sample can be put in a bag and analysed as such or it can be placed in
a sample cup and analysed with the XRF in stand mode (Figure 5). Using this procedure the XRF results
can be considered as semi-quantitative.
Figure 5 — Analysis of a wet sieved sample
Analysis of a dried and ground sample: If a mobile lab is present at the site under investigation, it can be
equipped with a drying oven (e.g. microwave) and grinding tools. Analysing a dried and finely ground
sample will significantly improve the accuracy and precision of the XRF results. The prepared sample can
be analysed with the XRF in stand mode (Figure 6). Using this procedure, one have to keep in mind that
longer testing times are required and that the sample throughput will be lower compared to the direct XRF
analysis.
Figure 6 — Analysis of a dried and ground sample
In a publication of C. Vanhoof et al [2] several types of XRF instruments were compared, together with the
influence of the applied preparation method on the acquired data using a field portable instrument. The
influence of the pretreatment on the acquired data is shown in Figure 7. Performing in situ analysis with the
2
field portable Spectrace 9000 resulted in low regression coefficients R of 0,7 for both elements. Also the
slopes were very low, therefore, the XRF values with a low concentration level were overestimated while the
higher levels were underestimated. A limited homogenisation (sieving over 2 mm) of the soil sample
significantly improved the regression parameters resulting in more comparable results.
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Figure 7 — Method comparison for the elements Zn and Pb, measured with the field portable EDXRF,
as a function of the pretreatment
These results confirm that in situ analyses are strongly influenced by the heterogeneity of the samples. A
limitation of the in situ analysis, without any homogenisation, is that only the surface top layer is analysed on
2
just a small soil area (± 5 cm ) corresponding to the XRF measuring window. Furthermore, the
homogenisation process also assure that the same sample will be analyzed by the XRF system and the
reference ICP-AES technique, while in situ analysis can be regarded as a one point surface analysis.
11
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Field analysis are particularly suitable to define ‘hot spots’ and to differentiate contaminated areas giving a
measure of the degree of contamination. For these purposes the sample strategy is of major concern to obtain
useful results. Further pretreatment i.e. drying and fine grounding of the soil sample, still improve the data
quality but less significant. However, the largest progress in achieving comparable data between the XRF and
the ICP-AES system is obtained when a minimal homogenisation is performed.
In commission of the RWS Waterdienst (The Netherlands) a similar study was performed by N. Walraven [3]
to evaluate the possibilities of XRF in order to measure Pb, Cu, Zn, As, Cd , Hg, Ni, Cr, Mo, Ba, Sn, V and Se
in sediments. The performance characteristics of the portable Niton XL3t 600 XRF analyser were determined
for the analysis of sediments, and special attention was spent to the evaluation of field moisture samples.
Using certified reference materials the accuracy of the XRF system was determined. In the project two
different hand-held Niton XRF systems were used (same type). Based on the results shown in Table 1, it can
be stated that different performance characteristics were obtained with the same type of XRF instruments.
Nevertheless it is possible to improve the calibration programme to obtain more accurate results. These data
confirm that it is a necessity to validate always the XRF i
...
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