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TRACE ELEMENT ANALYSIS USING EDXRF WITH POLARIZED OPTICS
Takao Moriyama1, Satoshi Ikeda1, Makoto Doi1 and Scott Fess2 1Rigaku Corporation, Takatsuki, Osaka 569-1146, Japan 2Applied Rigaku Technologies, Inc., Austin, TX 78717
ABSTRACT
We have developed an EDXRF spectrometer with polarized optics and new quantification
software which estimates non-measuring sample matrices using scattering intensities and full
profile fitting method combined with FP method. Accurate analysis down to ppm level can be
achieved even in complex sample composition with the quantification software. The
scattering FP method corrects for non-measuring components in samples such as coal fly ash,
soils and biological samples by using Compton and Thomson scattering intensities from a Mo
secondary target. Additionally, it is possible to analyze thickness and composition of
multi-layer thin films considering interlayer secondary excitation.
INTRODUCTION
Energy dispersive types of x-ray spectrometers are useful analytical tools for screening
analysis, such as for environmental applications, due to compact and easy sample handling.
However, the preparation of standard samples that match analyzing samples in applications
such as for industrial waste and recycling raw materials often requires special attention to
match sample types and preparation. This is because their sample matrices are complicated
and improved sensitivities for trace elements are demanded for these environmental
applications.
We have developed an EDXRF spectrometer with polarized optics and software using a
fundamental parameter method for accurate quantification combined with full profile fitting
method, including estimating non-measuring sample matrices using scattering intensities.
INSTRUMENT
The specifications of the new Rigaku EDXRF spectrometer NEX CG used in this study are as
follows:
X-ray tube : Pd target, air cooled
Tube power : 50W(50kV-2mA)
Secondary targets : 5 targets (max)
Detector : High performance SDD
(Silicon Drift Detector)
288Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 289Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website – www.dxcicdd.com
ICDD Website - www.icdd.com
Advances in X-ray Analysis, Volume 54
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Atmosphere : Vacuum, Air, He
Measuring area : 20mm diameter
METHODS
(1) Secondary targets with polarized optics optimized for low ppm applications
Secondary targets and polarized optics provide high P/B ratio spectra compared to direct
excitation optics in a wide energy range.
Blue and red lines in Fig. 1 show measurements of a multi-element oil sample by the
polarized optics and direct excitation optics, respectively. The polarized optics gives greatly
improved performance compared to the direct excitation optics for trace element analysis
(2) RPF-SQX (Rigaku Profile Fitting - Spectra Quant X) analysis
RPF-SQX is a standardless analysis
(Kataoka, 1989) software with a
fundamental parameters method for
accurate quantification combined with full
profile fitting method. This method is useful
for samples with complex matrices. Fig.2
shows an example of a fitted and measured
profile using the standard soil sample
JSAC0466. The fitted spectrum consists of
the sum of individually generated profiles
using the response function (Campbell and
Wang, 1992) for each element obtained by the FP method. Quantification results are obtained
by iteratively adjusting the fitted spectrum until it matches the measured spectrum. As shown
in Fig. 2, the calculated spectrum is in good agreement with the measured spectrum.
1.E+02
1.E+03
1.E+04
1.E+05
4 6 8 10 12 14 16 18
keV
Intensity (A
rb.U
nit)
EDXL300
Direct
Direct excitation optics
Polarized optics
X-ray tube
Secondary Targets
Sample
Detector
Pb-
L
Pb-
L
10 11 12 130
2000
4000
6000
8000
10000
Measure
Total profile
As profile
Se profile
Pb profile
Hg profile
X-r
ay in
tens
ity (
a.u.
)
Energy ( keV)10 11 12 13 keV
X-r
ay in
tens
ity (
a.u.
)
As -
K
Se-K
As -
K
Fig. 2. Measured and fitted spectra of the soil
standard JSAC0466S
Fig. 1. Polarized optics and measurement comparison to direct excitation optics
of an oil sample
289Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 290Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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(3) Scattering FP method for estimating non-measuring components
In the conventional FP method,
the information of all components
in a sample is required for
accurate analysis. The contents of
non-measuring elements can be
obtained when the elements and
the composition are known. For
example, �CH2� is set in
polyethylene as the balance.
However, when non-measuring
elements are not known, accurate calculation cannot be done using conventional fundamental
parameters (FP). The scattering FP method (Kataoka, et al., 2005) estimates the
non-measuring components from the scattering x-ray intensities of Compton and Thomson of
Mo-K line from the Mo secondary target as shown in Fig. 3. This method gives accurate
results for the applications having complex non-measuring components such a soil, scale and
so on.
RESULTS
Four typical application results are described below. The measurement conditions are
summarized in Table 6.
(A) Coal fly ash and soil
The hazardous element
analyses of fly ash and soil are
current topics in XRF analysis.
The CRMs of coal fly ash and
soil analyzed were measured by
loose powder method. Two
grams of the sample was set in
polyethylene sample cups of
32mm diameter opening with 4
um Prolene film support. Fig. 4
shows the spectra of the
samples of fly ash and soil
samples of NIST CRMs. It
shows the energy range for As,
Se and Pb and the peaks of the
trace elements are clearly detected. Table 1 and Table 2 list the analyzed results of hazardous
FP method
Non-measuring balance components are not known.
Metal
Polymer
Liquid
Scattering FP method
Soil, Scale, Waste oil
Non-measuring balance components are known.
Oxide
X-r
ay I
nten
sity
7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0keV
Fig. 4. Measured spectra of coal fly ash(NIST1633a:
blue line) and San Joaquin soil (NIST2709: red line)
in the range of 7 to 14 keV using Mo secondary
target
Fig. 3. Applicable samples of scattering FP method
290Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 291Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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elements and major elements, respectively. The RPF-SQX with the scattering FP method was
applied to the analysis of both samples. The analyzed results matched well with the certified
values even though the fly ash sample contains unburned carbon and the soil sample contains
organic matter.
(B) Thickness measurements of multilayer films on Si wafers
Multilayer thin film analysis is important in semi-conductor applications, as well as other
application such as photovoltaics. The multilayer thin film of Ti/Ni/Ag on Si wafers
illustrated in Fig. 5 were analyzed using the multilayer thin film FP software (Laguitton and
Mantler, 1977; Kataoka and Arai, 1990) and sensitivities of individual elements obtained by
measuring bulk pure metals are stored in the sensitivity library of the software for
standardless analysis. Table 3 lists the analyzed results of the two samples including repeat
measurement result to check the repeatability. The FP software in the NEX CG includes the
computation of the interlayer secondary excitation for accurate theoretical intensity
calculation. In this sample, secondary excitation calculation from Ni layer (Ni-K) to Ti
layer (Ti-K) is included. As shown in Table 3, good agreement between analyzed and
standard values was obtained without using standards with the same film structure.
(C) Biological samples
Analysis of mineral elements such as Mg, Ca and K and hazardous heavy elements are
important in biological samples. The CRMs of biological samples analyzed were prepared by
weighing 2 grams of the sample and making a hydraulically pressed pellet in 32mm of
diameter using 10 tons of pressure for 30 seconds. Fig. 6 shows the spectra of hazardous
heavy elements obtained by measuring various kinds of biological samples. The peaks of
several ppm of hazardous elements can be clearly seen. Fig. 7 shows the spectra of mineral
elements in plant and food samples. High P/B ratio could be obtained for the peaks of Na and
Table 1 Analyzed results of trace hazardous elements
Samples As
Cd Cr
Hg
Pb Se
San Joaquin Soil
Analyzed
17.9
n.d.
120.6
3.9
21.2
2.3
NIST2709
Std. Val. 17.7
0.4
130.0
1.4
18.9
1.6
Coal Fly Ash
Analyzed 149
n.d.
189
n.d.
75.8
12.6
NIST1633a
Std. Val.
145
1.0
196
0.16
72.4
10.3
Unit : ppm
Na
Mg
Al
Si
P S K Ca
Ti
Fe
San Joaquin Soil
Analyzed
1.35
1.84
7.93
29.26
0.063
0.090
1.95
2.02
0.34
3.51
NIST2709
Std. Val.
1.16
1.51
7.50
29.66
0.062
0.089
2.03
1.89
0.34
3.50
Coal Fly Ash
Analyzed
0.31
0.405
14.4
23.3
0.23
0.19
1.91
1.06
0.31
9.0
NIST1633a
Std. Val.
0.17
0.455
14.3
22.8
- - 1.88
1.11
- 9.4
Unit : mass% Table 2 Analyzed results of major elements
Samples
291Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 292Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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Mg by using a special secondary target for light element analysis equipped in the NEX CG
without interference of higher energy peaks as shown in Fig. 7 (c).
Table 4 shows the analyzed results of the aforementioned biological samples using the
RPF-SQX software with the scattering FP method. The influence of non-measuring elements
highly contained in these biological samples such as N, O, C and H, were effectively
corrected.
Si Wafer
Ag (1200A)
Ni (4000,2000A)
Ti (1000A)
Ti Ni Ag
n=1 976 3917 1166
2 978 3923 1177
3 983 3921 1167
4 970 3923 1185
5 976 3921 1196
6 968 3923 1169
7 970 3921 1212
8 990 3917 11699 973 3925 1201
10 968 3921 1172
Average 975 3921 1181
Std. dev. 7.1 2.6 16.4
RSD% 0.7 0.1 1.4
Ti Ni Ag
n=1 1066 2016 11772 1052 2013 1187
3 1056 2008 1170
4 1066 2013 1162
5 1066 2013 1201
6 1065 2020 1178
7 1065 2015 11928 1078 2012 1145
9 1064 2013 1171
10 1056 2015 1180
Average 1063 2014 1176
Std. dev. 7.3 3.1 15.8
RSD% 0.7 0.2 1.3
Unit:AngstromTi/Ni/Ag/Si Wafer
Unit:Angstrom
Fig. 5. Structure of
multilayer film
Table 3 Analyzed results of Ti/Ni/Ag film on Si Wafer Sample A
Sample B
292Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 293Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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(a)
Hg-
L
Se
As-
K
6.06 ppm 5.63 ppm
1.40 ppm
21.6 ppm
18.0 ppm
16.6 ppm
6.0
8.0 10.0 12.0 14.0keV
4.64 ppm
2.14 ppm
0.27 ppm
(b)
Hg -
L
X-r
ay I
nten
sity
keV9.6 10.0 10.4 10.8
Cd-
K
26.8 ppm
20.8 ppm
0.043 ppm
(c)
Ag-
K
keV
X-r
ay I
nten
sity
20.0 21.0 22.0 23.0 24.0
Heavy elements
5.0 5.4 5.8 6.2
X-r
ay I
nten
sity
keV
(d)
34.7 ppm
0.77 ppm
Cr -
K
X-r
ay I
nten
sity
Fig. 7. Spectra of Peach Leaves (NIST1547)
and Non-fat Milk Powder (NIST1549)
NIST1547:(a) RX9 secondary target, (b) Cu
secondary target
NIST1549:(c) Comparison of spectra
compared between RX9 secondary target and
special secondary target for light elements
Fig. 6. Spectra of marine organism standard samples of National Research Council Canada
Red lines : Lobster Hepatopancreas (TORT-2), Blue lines : Dogfish Muscle (DORM-2), Green
lines :Dogfish Liver (DOLT-2) (a) Mo secondary target, (b) magnified spectrum of (a) in
region of Hg, (c) Al secondary target, (d) Cu secondary target
(a)
X-r
ay I
nten
sity
keV1.4 1.8 2.2 2.6
1370 ppm
2000 ppm
360 ppm
(b)
X-r
ay I
nten
sity
2.8 3.2 3.6 4.0 4.4keV
2.43 mass%
1.56 mass%
Light elements
4970 ppm 1200 ppm
0.7 0.8 0.9 1.0 1.1 1.2 1.3
X-r
ay I
nten
sity
keV
Na-K á
Cl-
K e
scap
e-pe
ak
Na-
Ká
RX9 secondary target Secondary target for light elements(c)
Si-K
P-K
S-K
Cl-
K
Al-
K
Ca-
K
K-K
Na-
K
Mg-
K
293Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 294Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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(D) Copper Alloy
Copper alloy samples were analyzed as examples of trace element analysis in metal samples.
The copper alloy samples were polished using a lathe to make flat surface. Fig. 8 shows the
spectra obtained by measuring a naval brass standard. A Pb peak of 0.069mass% can be seen
with high P/B ratio due to the high speed detector with pile-up rejection and Mo secondary
target. Fig. 9 shows the spectra in the light element range obtained by measuring three copper
alloys containing phosphorous. Monochromatic Pd-L line effectively excites the P-K line
so that the peak of 90 ppm phosphorous could be seen in the spectrum. The detection of
P-K is difficult in WDXRF due to the interference by the 4-th order of Cu-K line. Table 5
exhibits the analyzed results of various kinds of copper alloys and the results match well with
the standard values from low level to high contents.
Fig. 8. Spectra of naval brass standard (NIST C1108) (a) Mo secondary target, (b) Al
secondary target
6.0 8.0 10.0 12.0 14.0 keV
10.0 11.0 12.0 13.0
Pb-
L
Pb-
L (a)
Alターゲット
20.0 24.0 28.0 32.0 36.0 keV
(b)
X-r
ay I
nten
sity
X-r
ay I
nten
sity
165.0 - NRCC DOLT-2 Analyzed
n.d. 27.7 90.8 14.2 5.7 23.7 2.0 2.7 21.1 n.d. 1.6
Dogfish Liver Std. Val. - 25.8 85.8 16.6 6.1 - - - 20.8 -
Samples
NIST1570aSpinach Leaves
NIES CRM No.1Pepperbush
Analyzed Std. Val.
Analyzed
Std. Val.
Samples
Ni Cu Zn As Se Br Rb Sr Cd Ba Hg ppmppmppmppmppmppmppmppmppmppmppm
2.1 2.2
12.2
14.0
82.0
80.0
- n.d.
-
n.d.
-
34.5
13.0 13.0
55.6
52.7
-
n.d. -
n.d.
- n.d
8.7 10.3
12.0
12.9
340.0
347.5
- n.d.
-
n.d.
-
0.8 75.0 75.5
36.0
35.0
6.7 5.7 165.5 n.d.
Table 4 Analyzed results of various biological samples
Na Mg Si P S Cl K Ca Mn Fe Co
mass% mass% mass% mass% mass% mass% mass% mass% ppm ppm ppm
NIST1570a Analyzed 1.83 0.85 0.11 0.59 0.50 0.65 2.79 1.47 66.5 271 n.d. Spinach Leaves Std. Val. 1.82 0.89 - 0.52 0.46 - 2.90 1.53 - - - NIES CRM No.1 Analyzed
n.d. 0.38 0.27 0.14 0.26 0.39 1.58 1.45 2021 215 15.6
Pepperbush Std. Val. - 0.41 - 0.11 - - 1.51 1.38 2030 205 23.0
NRCC DOLT-2 Analyzed
0.83 0.12 n.d. 1.08 1.29 0.83 0.87 0.06 5.7 1124 n.d. Dogfish Liver Std. Val. - - - - - - - - 6.9 1103 -
294Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 295Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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Table 6 Measurement conditions
(A) Coal fly ash and soil Atmosphere: helium
Secondary target Light element
target RX9 Cu Mo Al
kV-mA 25-auto *) 25-auto 50-auto 50-auto 50-auto
Energy ranges(KeV) 1.0-1.3 1.3-2.8 2.8-8.0 8.0-15.0 15.0-40.0
Counting time (s) 200 100 100 100 200
*) auto: current is adjusted such that dead time is at a predetermined level.
(B) Multilayer film Atmosphere: vacuum
Secondary target Cu Mo Al
kV-mA 50-auto 50-auto 50-auto
Energy ranges(KeV) 2.8-8.0 8.0-15.0 15.0-40.0
Counting time (s) 100 100 100
Table 5 Analysis results of copper alloy samples
Samples
Cu Zn Pb Fe Sn Ni Al Sb As Mn P mass% mass% mass% mass% mass% mass% mass% mass% mass% mass% mass%
NISTC1103
Free-CuttingBrass
Analyzed 59.1 35.6 3.88 0.25 0.869 0.17 n.d. n.d. n.d. n.d. 0.0045
Std. 59.19 35.7 3.81 0.26 0.88 0.16 - - - - 0.003 NISTC1108
Naval Brass Analyzed 65.0 34.4 0.069 0.048 0.397 0.031 n.d. n.d. n.d. 0.029 0.003 Std. 64.95 34.42 0.063 0.05 0.39 0.033 - - - 0.025 -
NISTC1115
CommercialBronze
Analyzed
88.1 11.6 0.011 0.127 0.102 0.070 n.d. n.d. n.d. 0.004 0.003
Std. 87.96 11.73 0.013 0.13 0.1 0.074 - - - - 0.005 NISTC1118
AluminumBrass
Analyzed
75.3 21.8 0.022 0.060 0.0047 n.d. 2.88 n.d. 0.009 0.002 0.133
Std. 75.1 21.9 0.025 0.065 - - 2.8 - 0.007 - 0.13 NISTC1119
AluminumBrass
Analyzed
77.2 20.2 0.053 0.028 n.d. n.d. 2.09 0.049 0.043 0.005 0.062
Std. 77.1 20.4 0.05 0.03 - - 2.14 0.05 0.04 - 0.07
Fig. 9. Spectra of light element range including phosphorus of copper alloys
Blue: NIST C1118, red:NIST C1119, green:NIST C1114
0.13mass%
0.07mass%
0.009mass%
0.8 1.0 1.2 1.4 1.6 1.8 2.0
2.2 2.4
keV
X-r
ay I
nten
sity
295Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 296Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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(C) Biological samples Atmosphere: vacuum
Secondary target Light element
target RX9 Cu Mo Al
kV-mA 25-auto 25-auto 50-auto 50-auto 50-auto
Energy ranges(KeV) 1-1.3 1.3-2.8 2.8-8.0 8.0-15.0 15.0-40.0
Counting time (s) 600 300 300 300 600
(D) Copper alloy Atmosphere: vacuum
Secondary target RX9 Cu Mo Al
kV-mA 25-auto 50-auto 50-auto 50-auto
Energy ranges(KeV) 1.0-2.8 2.8-8.0 8.0-15.0 15.0-40.0
Counting time (s) 100 50 50 50
CONCLUSION
The spectrometer with secondary targets, polarized optics, and high speed detector with
pile-up rejection demonstrated extremely high P/B ratios from light to heavy elements
resulting in low LLD results. Accurate analyses down to ppm level could be achieved even in
complex sample composition for the quantification software which combined fundamental
parameter method and full profile fitting. The scattering FP method corrected for
non-measuring components in samples such as soils, biological samples by using Compton
and Thomson scattering intensities from Mo secondary target.
Additionally, good results of multilayer thin films could be obtained by the thin film FP
software considering interlayer secondary excitation.
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method using sensitivity library), The Rigaku Journal, 6, 33-39.
Kataoka, Y. and Arai, T. (1990), �Basic studies of multi-layer thin film analysis using
fundamental parameter method�, Advances in X-ray Analysis, 33, 213-223.
Kataoka, Y., Kawahara, N., Hara, S., Yamada, Y., Matsuo, T. and Mantler, M. (2005),
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296Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 297Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54
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x-ray fluorescence analysis�, Advances in X-ray Analysis, 20, 515-528 .
297Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 298Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54