NAA Application at the INCT
Halina Polkowska-Motrenko
Institute of Nuclear Chemistry and Technology, Warsaw, Poland
The Institute of Nuclear Chemistry and Technology
(INCT) was established in 1983 after partition of the
Institute of Nuclear Research in which it formerly
existed as a Chemistry Division.
The Institute has a leading role in Poland in
implementing nuclear technologies, methods and
instruments.
The INCT is appointed as the main institution
responsible for the development and implementation
of nuclear analytical techniques in Poland.
The Department of Analytical Chemistry of the INCT
has been involved in the elaboration of INAA and
RNAA methods for determination of selected elements
in many different materials.
INAA has been applied for multielemental analysis of
rare
and
precious
samples
e.g.
meteorites,
concentrates and wastes from copper industry, forensic
samples etc. and also for homogeneity testing of
candidate CRMs.
Elemental standardization is used. Contents of up to 23
elements can be quantified on the basis of
determination of medium- and long-lived radionuclides.
RNAA methods has been applied for determination
of selected trace elements in different samples.
Many radiochemical separation schemes enabling
selective and quantitative separation of selected
elements have been elaborated. Mainly ionexchange and extraction column chromatography
but also liquid extraction and distillation have
been applied.
The INCT has developed a concept of the high-accuracy
(definitive) RNAA methods on selected elements in
biological matrices and such methods have been elaborated
since 1986. The high-accuracy RNAA methods are applied
in the certification process of CRMs for inorganic
trace analysis as well as for the validation of other
analytical procedures.
High accuracy RNAA methods
for selected elements in biological matrices
• methods of guaranteed accuracy
based on combination of:
• neutron activation
• very selective and quantitative postirradiation separation of indicator
radionuclide by column chromatography
• gamma-ray spectrometric measurements
Basic steps in devising high-accuracy RNAA method
Devising of mineralization method
and separation scheme involving
column chromatography
Checking with the aid of radioactive
tracers whether there is 100%
recovery and high radiochemical
purity of the analyte fraction
No
Yes
NEUTRON IRRADIATION
samples, standards, CRMs,
blanks, neutron flux monitors
Yes
Radiochemical separation samples and one standard
gamma-ray spectrometric measurements of
samples and all standards
Checking if all qualifying criteria have been met
No
No
result is not
accepted
Ye
s
Result is accepted as obtained
by the high-accuracy method
The high-accuracy RNAA method is designed and
elaborated according to rules assuring high accuracy:
• All conditions should be optimized enabling selective
isolation of an element with 100% yield confirmed by
tracer experiments,
• All potential sources of errors starting from sampling
and sample dissolution up to gamma-spectrometric
measurements should be identified at a stage of
elaborating the method, and removed or appropriate
corrective actions introduced into the procedure.
• Whenever possible, the color of the ion in question (or
its complex) added as a carrier should be used for
visual control to safeguard against unexpected failure
of the separation procedure
• With each set of samples at least two standards
should be irradiated, one of which is later on processed
exactly as are the samples and the other is not. The
specific activities of both standards should agree within
predetermined limits;
• Residual blank resulting from the contact of the
sample with sample container should be measured in
each series of determinations;
In principle, the method should be a single element
one while all parameters can be optimized with
respect to this particular element.
The method is equipped with some classification
criteria providing protection against making gross
errors. The criteria are as follows:
• Visual control of the correctness of the separation
procedure: in the retention stage on the chromatography
columns the color band of analyte should not travel more
than 1/3 of the bed length
• Residual blank (may originating form the contact of the
sample with packing material) is small (below a few
percent of the analyte contents in analyzed sample)
• Agreement of standards: the standard which has
passed the whole analytical procedure should agree within
predetermined limits (ca. few percent) with that measured
directly
• The result for at least one CRM irradiated and
analyzed together with the samples should be in
agreement with the certified value
The result has to fulfil all of criteria to be accepted.
1000
100
200
300
400
500
Cd 527.7 keV
11 5
Cd 492.5 keV
Cd -
11 5
115m
In 336.6 keV
3000
11 5
Cd 261 keV
11 5
Cd 231 keV
11 5
Counts per channel
4000
2000
0
600
700
Energy, keV
800
900
1000
1100
1200
The limit of detection of the method has
amounted to 0.5 ng g-1.
The results obtained by this method are in
excellent agreement with certified values
for the CRMs spanning the Cd concentration
range of more than 5 orders of magnitude.
3
10
y = 0.98805x + 0.02852
2
R = 0.99992
8
2
Experimental values mg g
-1
10
1
10
7
0
10
6
5
-1
10
3
4
-2
10
2
1
-3
10
-3
10
-2
10
-1
10
0
10
Certified v alues mg g
1.
2.
3.
4.
Ve rsieck ' s H uma n Ser um
IAE A H -4 Anim al Muscle
IN CT- TL -1 Te a Le av es
IAEA H- 9 H um an Die t
5.
6.
7.
8.
1
10
2
10
-1
IN CT- MPH- 2 Mix ed Po lish He rbs
CT A-O T L-1 Or ienta l T obacc o Le av es
IAE A MA-M -2 Mussel T issue
IAEA H- 8 H or se Kidne y
Determina tion of Cd by the de finitive method
in the ce rtified re fe re nce ma teria ls
3
10
The results are also precise as can be seen when the results are
shown on the background of Horwitz and Thompson and Lowthian
curves representing variation of reproducibility precision
140
120
Thompson and Lowthian curve
RSD (%)
100
80
(Horwitz curve) x 1/2
60
40
Horwitz curve
20
0
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
-1
Mass fraction, (g g )
1E-4
1E-3
This method can be also apply for Ni
determination when the samples are
irradiated with the high flux of fast neutrons
by reaction
58Ni(n,p)58Co
The limit of detection for Co amounted to
4x10-2 ng g-1 and 20 ng g-1 for Ni.
High accuracy RNAA method for the determination
of Mo in biological materials
Nuclear reaction used for Mo determination
98Mo(n,γ)99Mo
99mTc
may be subjected to interference originating from
the nuclear fission reaction
235U(n,f)99Mo
99mTc
The elaborated analytical scheme allows for the
simultaneous determination of trace amount of Mo
and U in biological materials.
Uranium is determined by the reaction:
238U(n,γ)239U
239Np
The detection limits amounted 0.15 ng g-1
for U and 2.5 ng g-1 for Mo.
Uncertainty budget for Co determination in INCT-Tl-1 Tea Leaves
source of uncertainty
unit
value
Mass of sample
mg
250
Mass of standard
mg
20
Mass of neutron flux monitor
mg
50
Residual blank
ng
0.01
Neutron flux gradient
1.00±0.025
Neutron self-shielding/scattering
Sample counting statistics
30000
Standard counting statistics
30000
Counting positioning of sample
Counting positioning of standard
Pulse pile-up effect - sample
Pulse pile-up effect – standard
Peak calculation – sample
Peak calculation – standard
Radiochemical separation
1.00 ± 0.06
Mass fraction of Co: 399 ng g-1  10.4 ng g-1 (k=2) (2.6%)
Certified value 387 ng g-1  42 ng g-1
Rel. std.
uncertainty, %
0.1
0.1
0.1
0.1
0.1
0.2
0.6
0.8
0.3
0.4
0.1
0.1
0.2
0.2
0.4
Uncertainty budget for Mo determination in NIST 1547 Peach Leaves
Rel. std.
uncertainty, %
Mass of sample
mg
150
0.1
Mass of standard
mg
20
0.1
Residual blank
mg
0
0.1
Neutron flux gradient
1.00± 0.025
0.1
Interfering reaction
ng
2
2.1
Neutron self-shielding/scattering
0.2
Sample counting statistics
Bq /counts
3000
1.8
Standard counting statistics
Bq /counts
150000
0.4
Counting positioning of sample
0.3
Counting positioning of standard
0.3
Pulse pile-up effect - sample
0.1
Pulse pile-up effect – standard
0.1
Peak calculation – sample
0.2
Peak calculation – standard
0.2
Radiochemical separation
1.00 ± 0.01
0.6
Mass fraction of Mo: 58 ng g-1  3.4 ng g-1 (k=2) (5.8%)
-1
-1
Certified value 60 ng g  8 ng g
source of uncertainty
unit
value
In 1998 CCQM adopted the following definition of
primary method of measurement (PMM).
A primary method of measurement is a method
having the highest metrological qualities, whose
operation can be completely described and understood,
for which a complete uncertainty statement can be
written down in terms of SI units.
A primary direct method measures the value of an
unknown without reference to a standard of the same
quantity.
A primary ratio method measures the value of a ratio
of an unknown to a standard of the same quantity, its
operation must be completely described by
a
measurement equation.
As can be seen for the high-accuracy RNAA
methods,
the expanded uncertainty (k=2)
varies from 2.6% for more favorable case of Co
determination to 5.8% for the less favorable
case of Mo determination. Such values are
characteristic for the methods of the highest
metrological qualities.
The high-accuracy RNAA methods have the
detection limits of the order of ng g-1 and provide
the results with very low value of uncertainty,
traceable to SI units. The methods can be fully
described by measurement equations.
The above statement means that the high-accuracy
RNAA method fulfils the CCQM definition of a primary
ratio method (PMM) and can be complementary to
isotope-dilution mass spectrometry (IDMS).
IDMS is the only one trace analysis method indicated by the
CCQM so far as PMM.
From the point of view of QA/QC of chemical
measurements it is very important that at least two
trace analysis PMMs based on different chemical
principles can be available.
Despite of the advantages of IDMS, this method
has also some limitations like the all other
analytical techniques.
The high-accuracy RNAA method can serve for
checking accuracy of the other methods used
in analytical chemistry and can be applied in
the certification of CRMs.
Preparation and certification of CRMs
• In the INCT the certification of the candidate
reference materials is performed on the basis of
worldwide ILC.
• The applied methods of data evaluation and
classification criteria have been the same with
only minor modifications.
• The adopted approach of data evaluation is based
on outlier’s rejection procedure which uses
concurrently four statistical criteria (Dixon,
Grubbs, skewness and kurtosis) at the
significance level of 0.05, followed by calculation
of overall means of laboratory means remaining
after outlier rejection, standard deviations,
confidence intervals etc.
Whenever possible, the process of assigning of
reference values is confirm by comparison of
assigned values with results obtained by the highaccuracy RNAA method.
Assigning of certified value for Cd in CTA-OTL-1
High-accuracy RNAA result
Certified value
Range after outlier rejection
Original data range
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
The same material CTA-OTL-1 was analyzed in the
course of ILCs organized by the INCT
• in the year 1991 (as a candidate reference
material CTA-OTL-1)
• and the later years 2000 and 2003 (as an
unknown to participants reference material
accompanying new candidate RMs).
In the following figures the comparison of certified
values with the values obtained by the highaccuracy RNAA method can be seen.
Cd
2006
2004
2002
2000
1998
1996
1994
1992
1990
high-accuracy RNAA method
0,5
0,7
0,9
1,1
mg/kg
1,3
1,5
Co
2006
2004
2002
2000
1998
1996
1994
1992
1990
high-acuracy RNAA method
0,4
0,6
0,8
1
mg/kg
1,2
1,4
Ni
2006
2004
2002
2000
1998
1996
1994
1992
1990
high-accuracy RNAA method
3
4
5
6
mg/kg
7
8
9
Zn
2005
2000
1995
1990
40
45
50
55
mg/kg
60
65
In all figures, the good agreement of originally certified
values with those that could be assigned on the basis of
results from 2000 and 2003 ILCs has been obtained. The
mean values with their confidence limits always overlap.
The assigned values agree well with the results obtained
by the high-accuracy RNAA methods.
Good agreement of the mean values obtained in the
period of more than 10 years, as well as with the
results obtained by the high-accuracy RNAA
methods shows a correctness of the adopted
procedure of assigning certified values.
Concluding:
INAA procedures applied at the INCT enable the
determination of up to 23 elements in one sample
INAA procedure has been elaborated and used for
testing of homogeneity of candidate RMs
Many RNAA procedures have been elaborated
enabling radiochemical separation of selected
elements from various irradiated materials and
their determination at very low level
The high-accuracy RNAA methods meeting
requirements of PMM have been elaborated for
Cd, Co, Cu, Ni, Mo and U determination in
biological materials.
Thank you for your attention.