Determination of long-lived radionuclides at ultratrace level using advanced mass spectrometric ...

129 Pages·2005·5.05 MB·English

Forschungszentrum Jülich
in der Helmholtz-Gemeinschaft
Geschäftsbereich Sicherheit und Strahlenschutz
Zentralabteilung für Chemische Analysen
Determination of long-lived radionuclides
at ultratrace level using advanced mass
spectrometric techniques
Myroslav Zoriy
Jül-4187
Berichte des Forschungszentrums Jülich 4187
Determination of long-lived radionuclides
at ultratrace level using advanced mass
spectrometric techniques
Myroslav Zoriy
Berichte des Forschungszentrums Jülich ; 4187
ISSN 0944-2952
Geschäftsbereich Sicherheit und Strahlenschutz
Zentralabteilung für Chemische Analysen Jül-4187
(Diss., Prag, Univ., 2005)
Zu beziehen durch: Forschungszentrum Jülich GmbH · Zentralbibliothek
D-52425 Jülich · Bundesrepublik Deutschland
콯 02461 61-5220 · Telefax: 02461 61-6103 · e-mail :
Abstract

Determination of long-lived radionuclides at sub-fg concentration level is a challenging
task in analytical chemistry. Inductively coupled plasma mass spectrometry (ICP-MS)
with its ability to provide the sensitive and fast multielemental analysis is one of the most
suitable method for the measurements of long lived radionuclides in the trace and ultra
trace concentration range.

In present the Ph.D. study a variety of procedures have been developed permitting the sub
-1 226
fg ml determination of long-lived radionuclides (e.g. U, Th, Pu) as well as Ra (T1/2 =
90
1600 y) and Sr (T1/2= 28.1 y) in different samples. In order to avoid isobaric
interferences, to increase the sensitivity, precision and accuracy of the methods the
application of different techniques: pre-concentration of the sample, off-line separation
on the crown resin, measurements under cold plasma conditions, using microconcentric
nebulizers (e.g DIHEN, DS-5) or the application of LA-ICP-MS for sample introduction
have been studied.

The limits of detection for different radionuclides was significantly improved in
comparison to the ones reported in the literature, and, depending on the method applied,
-15 -18 -1 239
was varied from 10 to 10 g ml concentration range. For instance, the LOD for Pu
in 1 l of urine, based on an enrichment factor (due to the Ca3(PO4)2 co-precipitation) of
?�18 ?�18 ?�1
100 for PFA-100 nebulizer and 1000 for DIHEN, were 9×10 and 1.02×10 g ml ,
respectively.

239
Pu was detected (after the enrichment) in 100L of the Sea of Galilee at a concentration
-19 -1 240 239
level of about 3.6 × 10 g ml with a Pu/ Pu isotope ratio of 0.17. This measured
plutonium isotope ratio is the most probable evidence of plutonium contamination of the
Sea of Galilee as a result of global nuclear fallout after the nuclear weapons tests in the
sixties.

i
A sensitive analytical procedure based on nano-volume flow injection (FI) and
inductively coupled plasma double-focusing sector field mass spectrometry (ICP-SFMS)
was proposed for the ultratrace determination of uranium and plutonium. A 54-nl sample
was injected by means of a nano-volume injector into a continuous flow of carrier liquid
-1 -17
at 7 ?�L min prior to ICP-SFMS. The absolute detection limits were 9.1×10 g (3.8 ×
-19 238 -17 -20 242
10 mol, ~230 000 U atoms) and 1.5 × 10 g (6 × 10 mol, ~38 000 Pu atoms)
for uranium and plutonium, respectively.

90 239 240
The Sr, Pu and Pu at the ultratrace level in groundwater samples from the
Semipalatinsk Test Site area in Kazakhstan have been determined by the developed ICP-
90
SFMS method. In order to avoid possible isobaric interferences at m/z 90 for Sr
90 + 40 50 + 36 54 + 58 16 + 180 2+
determination (e.g. Zr , Ar Cr , Ar Fe , Ni O2 , Hf , etc.), the measurements
were performed at medium mass resolution under cold plasma conditions. Pu was
separated from uranium by means of extraction chromatography using Eichrom TEVA
90 239 240
resin with a recovery of 83%. The limits of detection for Sr, Pu and Pu in water
?�1 90
samples were determined as 11, 0.12 and 0.1 fg ml , respectively. Concentrations of Sr
239
and Pu in contaminated groundwater samples ranged from 18 to 32 and from 28 to 856
?�1 240 239
fg ml , respectively. The Pu/ Pu isotopic ratio in groundwater samples was
measured as 0.17, which indicates the most probable source of contamination - nuclear
weapons tests at the Semipalatinsk Test Site conducted by the USSR in the 1960s

The LA-ICP-MS was used in present work for the determination of naturally occurred
long lived radionuclides (e.g. U, Th) in different kinds of solid samples (2D gel of
separated proteins, thin cross section of human brain tissue, biological samples [flower
leafs]). An unique cooled laser ablation chamber (using two Peltier elements) was
designed for these experiments. Using this chamber the precision and accuracy of the
measurements were improved up to one order of magnitude and was found to be very
advantageous in comparison to the non-cooled laser ablation chamber. The precision of
234 238
the measurements of e.g. uranium isotope ratios in the range of 2.0–1.6% for U/ U,
235 238 236 238
1.3–0.4% for U/ U and 2.1–1.0% for U/ U in selected uranium isotopic standards
reference material were determined by microlocal analysis (diameter of laser ablation
ii
crater: 15, 25 and 50 ?�m) using LA-ICP-MS with a cooled laser ablation chamber. The
234 238 235 238 236 238
accuracies of U/ U, U/ U and U/ U isotope ratios varied in the range of 4.2–
1.1%, 2.4–0.5% and 4.8–1.1%, respectively, and were dependent on the diameter of the
laser beam used.

In addition to the analysis of long lived radionuclides, some other elements, that can
present potential interest to the analyzed sample, were measured within the framework of
the present study. Laser ablation inductively coupled plasma mass spectrometry (LA-
ICP-MS) was used to produce images of element distribution in 20-?�m thin sections of
2
human brain tissue. The sample surface was scanned (raster area ~80 mm ) with a
focused laser beam (wavelength 213 nm, diameter of laser crater 50 ?�m, and laser power
9 -2
density 3×10 W cm ) in a cooled laser ablation chamber developed for these
measurements. Cross sections of human brain samples – hippocampus as well as brain
tissues infected and non-infected with Glioblastoma Multiforme (tumor cells) were
analyzed with the developed procedure. An inhomogeneous distribution (layered
structure) for P, S, Cu, and Zn in thin brain sections of the hippocampus were observed.
In contrast, Th and U were more homogeneously distributed at a low-concentration level
-1
with detection limits in the low-ng g range.

P, S, Si, Fe, Cu and Zn were measured by LA-ICP-MS in human brain proteins, separated
by 2D gel electrophoresis. Quantification procedure was carried out using the sulphur
(determined by MALDI-FTIR-MS) as an internal standard. In addition to the essential
elements, U and Th were determined in some proteins spot in 2D gel electrophoresis. The
-1
LODs of 0.01 ?�g g for both radionuclides were observed.

iii
Contents

1. Motivation of the work

2. Measurements techniques for determination of long-lived radionuclides

2.1. Overview of most important techniques for long lived radionuclides
determination (e.g RIMS, AMS, TIMS etc)
2.2. Capability of ICP-MS for analysis of long lived radionuclides.

3. Fundamentals and principle of ICP-MS

3.1. Sample introduction system
3.2. Ion generation in inductively coupled plasma
3.3. Ion extraction
3.4. Ion separation in mass analyzer
3.5. Ion detection

4. Separation and pre-concentration methods

4.1. Possible on-line separation (Capillary electrophoresis (CE) separation)
4.2. Off-line separation (extraction chromatography, co-precipitation)
4.3. Pre-concentration methods

5. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

5.1. Application of LA-ICP-MS for determination of long lived radionuclides
5.2. Basics and instrumentation of LA-ICP-MS

6. Experimental part

6.1. Instrumentation

6.1.1. Optimization and experimental parameters of double focusing ICP-MS
(ICP-SFMS)
6.1.2. Advanced solution introduction systems (Aridus, USN, DIHEN, nano-
FI-ICP-MS)
6.1.3. Laser ablation ICP-MS
6.1.3.1. Experimental parameters of LA-ICP-MS
6.1.3.2. LA-ICP-MS with cooled LA-chamber

6.2. Quantification and evaluation of analytical data

iv
6.2.1. External calibration using standards reference materials
6.2.2. Standard addition method
6.2.3. Isotope dilution analysis
6.2.4. Solution based calibration in LA-ICP-MS

6.3. Samples preparation

6.3.1. Pre-concentration of actinides
6.3.1.1.Co-precipitation of actinides with MnO2 and Fe(OH)3 from large
volumes of water samples
6.3.1.2.Co-precipitation of actinides with Ca(PO3)2 from urine samples
6.3.1.3.Co-precipitation on crown ether resins

6.3.2. Samples separation from complex matrices

6.3.2.1.Extraction chromatography protocols
6.3.2.1.1. Actinide separation on TEVA-resin
6.3.2.1.2. Actinide separation on UTEVA-resin
6.3.2.1.3. Separation of Sr on “Sr-specific” resin
6.3.2.1.4. Ra separation on “Ra specific” disk

6.3.3. Sample preparation procedure for ICP-SFMS measurements of urine
samples

6.4. Isotopes standards, standard reference materials and chemicals

7. Results and discussions

7.1. Methodical development for analysis of actinides by ICP-SFMS

236 236 238
7.1.1. Improvement of LOD for U and minimum U/ U detectible
isotope ratio
7.1.2. Minimization of necessary sample volumes for ICP-MS actinide
analysis
7.1.2.1. DIHEN-ICP-MS measurements of uranium standard isotopic
reference materials
7.1.2.2. Application of nano-FI-ICP-MS for determination of actinides at
ultratrace concentration level

7.2. Determination of long lived radionuclides at ultratrace concentration level by
ICP-MS

237
7.2.1. Determination of plutonium, americium and Cs at ultratrace level in
soil samples
v