Verlag des Forschungszentrums Jülich
JUEL-4187
Zoriy, Myroslav
Determination of long-lived radionuclides at ultratrace level using advanced mass spectrometric techniques
123 S., 2005
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
fg ml-1 determination of long-lived radionuclides (e.g. U, Th, Pu) as well as 226Ra (T1/2 =
1600 y) and 90Sr (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,
was varied from 10-15 to 10-18 g ml-1 concentration range. For instance, the LOD for 239Pu
in 1 l of urine, based on an enrichment factor (due to the Ca3(PO4)2 co-precipitation) of
100 for PFA-100 nebulizer and 1000 for DIHEN, were 9×10-18 and 1.02×10 -18 g ml-1 ,
respectively.
239Pu was detected (after the enrichment) in 100L of the Sea of Galilee at a concentration
level of about 3.6 × 10-19g ml-1 with a 240Pu/239Pu 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.
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
at 7 L min -1 prior to ICP-SFMS. The absolute detection limits were 9.1×10-17 g (3.8 ×
10-19 mol, ~230 000 238U atoms) and 1.5 × 10-17 g (6 × 10-20 mol, ~38 000 242Pu atoms)
for uranium and plutonium, respectively.
The 90Sr, 239Pu and 240Pu at the ultratrace level in groundwater samples from the
Semipalatinsk Test Site area in Kazakhstan have been determined by the developed ICPSFMS
method. In order to avoid possible isobaric interferences at m/z 90 for 90Sr
determination (e.g. 90Zr+, 40Ar50Cr+, 36Ar54Fe+,
58Ni16O2+, 180Hf2+, 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
resin with a recovery of 83%. The limits of detection for 90Sr, 239Pu and 240Pu in water
samples were determined as 11, 0.12 and 0.1 fg ml1 , respectively. Concentrations of 90Sr
and 239Pu in contaminated groundwater samples ranged from 18 to 32 and from 28 to 856
fg ml1 , respectively. The 240Pu/239Pu 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
the measurements of e.g. uranium isotope ratios in the range of 2.0–1.6% for 234U/238U,
1.3–0.4% for 235U/238U and 2.1–1.0% for 236U/238U in selected uranium isotopic standards
reference material were determined by microlocal analysis (diameter of laser ablation
crater: 15, 25 and 50 m) using LA-ICP-MS with a cooled laser ablation chamber. The
accuracies of 234U/238U, 235U/238U and 236U/238U 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 (LAICP-
MS) was used to produce images of element distribution in 20-m thin sections of
human brain tissue. The sample surface was scanned (raster area ~80 mm2) with a
focused laser beam (wavelength 213 nm, diameter of laser crater 50 m, and laser power
density 3×109 W cm-2) 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
with detection limits in the low-ng g-1 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
LODs of 0.01 g g-1 for both radionuclides were observed.
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