Journal of Nuclear and Radiochemical Sciences, Vol. 15, No.1, pp. 7-13, 2015

ArticlesEvaluation of a new sector-field ICP-MS with Jet Interface for ultra-trace determination of
Pu isotopes: from femtogram to attogram levels
J. Zheng*
Research Center for Radiation Protection, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage,
Chiba 263-8555, Japan
Received February 19, 2015; Received in revised form April 27, 2015; Accepted May 12, 2015
In March 2014, a new sector-field (SF)-ICP-MS (Element XR) equipped with the Jet Interface was installed in the
Research Center for Radiation Protection at the National Institute of Radiological Sciences (NIRS). This is thefirst Element XR installed for actinides measurements in Japan. In this paper, a detail evaluation is made of the
Element XR on its analytical potential for ultra-trace determination of Pu isotopes. In order to enhance the sensitivity for Pu isotope analysis, high efficiency sample introduction systems (APEX-Q and Aridus II) were combinedwith the Element XR. A certified Pu isotope standard solution (NBS 947) and a multi element standard solution(Merck Multi Element Standard), which contained depleted U, were used to investigate four items: the formation
rate of 238UH+, which could interfere with an ultra-trace level 239Pu determination; the detection limit for Pu; theprecision and accuracy for 240Pu/ 239Pu atom ratio measurement; and the long-term (8- month) stability for Pu isotope composition analysis. Due to the exceptionally high sensitivity of the new SF-ICP-MS, a detection limit at
the attogram (10 -18 g) level was achieved. This is comparable to or even surpasses the detection limit of accelerator
mass spectrometry, which has long been regarded as the most sensitive technique for Pu isotope measurement.

1. Introduction
Essentially all of the Pu found in the environment is ofanthropogenic origin, and it is a product of human activities(such as atmospheric nuclear weapons testing, reprocessing of
nuclear fuel, and releases from nuclear accidents) of the pastseven decades, although trace amounts of 239Pu and 244Pu arepresent naturally either from a primordial Earth origin or fromneutron capture by 238U [1-4]. Due to the high radiological toxicities and very long radioactive half-lives, Pu isotopes are
regarded as highly hazardous contaminants in the environment,
and the most frequently monitored Pu isotopes are 238Pu, 239Pu,
240
Pu and 241Pu with half-lives of 87.7 y, 24110 y, 6561 y and14.4 y, respectively [5]. The isotopes 238Pu, 239Pu, and 240Pu all
decay by emission of α particles, while 241Pu undergoes β decay
to produce 241Am. It was well-known that Pu isotopic compositions (238Pu/ 239+240Pu activity ratio, 240Pu/ 239Pu atom ratio and241
Pu/ 239Pu atom ratio) vary significantly in the environment
depending on the emission source [6], the Pu isotopic ratio,
therefore, has been used as a fingerprint for contamination
source identification. Although 238Pu/ 239+240 Pu activity ratio
has been used for contamination identification for a long-time,
its measurement with alpha spectrometry is time consuming.
With the development of ICP-MS technique, rapid determination of 240 Pu/ 239Pu and 241Pu/ 239Pu atom ratios is achievable.
Thus, the use of atom ratios of 240Pu/ 239Pu and 241Pu/ 239Pu has
been found wider applications for contamination source identification. For example, the atom ratio of 240 Pu/ 239 Pu allows
weapons-grade Pu (0.01-0.05) to be distinguished from reprocessing Pu (0.2-0.8) and global fallout Pu (0.17-0.19), and thetransport of Pu from different sources to be studied [7].
In recent years, there has been an increasing demand for
ultra-trace determination of Pu isotopes in studies on radiation
protection [8], safeguards and nuclear forensics [9,10], andenvironmental studies, such as tracing the sources of radioactive contamination, revealing the transport process of aerosols*Corresponding author. E-mail: jzheng@nirs.go.jp Tel: 81-043206-4634 Fax: 81-043-255-0721

in the atmosphere, establishing new geochronology [11,12], andin investigating ongoing environmental changes, for instance,
soil erosion and desertification [13-15]. Conventionally, alpha
spectrometry has usually been used for Pu measurement invarious environmental samples. This method, however, normally requires a tedious chemical separation procedure andlong counting times (days to weeks). Moreover, alpha spectrometry cannot distinguish 239Pu and 240Pu due to the closenessof the alpha radiation energies (5.16 MeV and 5.17 MeV for239
Pu and 240 Pu, respectively), so it cannot provide isotopic
composition information. In contrast, mass spectrometry,especially ICP-MS, as an atom-counting approach that counts
the atoms themselves, irrespective of their decay mode, specific activity, or half-life, is gradually replacing alpha spectrometry as a main-stream technique for Pu isotopic analysis.
Due to the strength of the argon plasma source used for ICPMS, almost 100% ionization efficiency can be achieved for Pu
isotopes with the first ionization potential of 6.03 eV as calculated from the Saha equation, thus, highly sensitive determination of Pu isotopes can be realized. Recent development of
ICP-MS techniques, especially sector-field (SF)-ICP-MS, haspushed the detection limit for analysis of Pu isotopes down to
the sub-femtogram level [16-19].
A new SF-ICP-MS, Element XR equipped with the Jet
Interface was installed in the Research Center for Radiation
Protection at the National Institute of Radiological Sciences(NIRS) in March 2014. As this Element XR is the first inJapan to be installed for actinide analysis, a detailed investigation was made on its analytical potential for Pu isotopes. In
combination with the high efficiency sample introduction systems (APEX-Q and Aridus II), an exceptionally high sensitivity was obtained, and a detection limit at the attogram (10 -18 g)
level was achieved, which is comparable to or even better thanthe detection limit of accelerator mass spectrometry (AMS).
2. Experimental
2.1. Explanation and features of the Element XR. The
Element XR (Thermo Scientific, Bremen, Germany) was devel-© 2015 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 06/04/2015

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Zheng

J. Nucl. Radiochem. Sci., Vol. 15, No. 1, 2015

oped from the Element 2 by introducing a high efficient sample
interface, the Jet Interface, to further improve the sensitivity.
Thus, like the Element 2, the Element XR is a high performance, double-focusing magnetic SF-ICP-MS with the capability for rapid multi-element and isotopic ratio measurements.
The important instrumental characteristics of the Element XR
can be briefly summarized as follows [20].
(1) Plasma ion source and interface: the argon plasma ion
source and sampling interface of the Element XR are at ground
potential, which reduces the initial kinetic energy spread, thusincreasing the ion transmission and delivering high sensitivity
at all resolutions. The Jet Interface, which consists of a highcapacity dry interface pump and the Jet sampler cone, further
increases the sensitivity required for long-lived radionuclides
analysis.
(2) Detection system: the Element XR has a discrete dynodedetector system, so the ion beam does not have to directly
strike the detector to initiate an electron cascade. The secondary electron multiplier uses a conversion dynode at -8 kV, producing a uniform response across the mass range. By
incorporating a single Faraday detector, the detection system of
the Element XR raises the linear dynamic range to >1012 ordersof magnitude, thus trace and major elements can be quantified
in a single analysis.
2.2. Outline of the high efficiency sample introduction
systems: APEX-Q and Aridus II. Figure 1 shows schematic

diagrams of the SF-ICP-MS (Element XR) coupled to the highefficiency sample introduction systems (APEX-Q and AridusII) and Table 1 lists some of the instrument and data acquisition settings.
The APEX-Q is a desolvation sample introduction system(Element Scientific Inc., USA) for ICP to enhance sensitivity
and lower formation of H 2O-origin background species, suchas UO + and uranium hydrides (UH + and UH 2 +) which caninterfere with 239 Pu and 240 Pu determination. A nebulizer
sprays the sample mist at 100 °C into a heated cyclonic spraychamber, the mist is subsequently cooled with a peltier-cooled
multipass condenser to 2 °C , and then it is transported to thedesolvation membrane module (ACM Nafion fluoropolymer
membrane desolvation module). A countercurrent flow of Ar
sweep gas is introduced to remove solvent vapors that permeate
the membrane wall. Nonvolatile sample components do notpass through the membrane wall; instead they continue to the
SF-ICP-MS torch injector where they are ionized in the plasma.
Thus, only dry aerosol particles are loaded to the plasma. Thissystem can be used with different nebulizers that provide awide range of sample uptake rates from 20 μL min-1 to over 1
mL min -1. The nebulizers can be either self-aspirated or
pumped. Because the spray chamber is heated to 140 °C andthe condenser is at 2 °C, the generated aerosols are uniform
and have only a small amount of moisture. The improved sensitivity of the APEX-Q is due to the increase of both the sample
transport efficiency and the aerosol quality. Further sensitivity

Figure 1. Schematic diagrams of the SF-ICP-MS (Element XR) coupled to the APEX-Q and Aridus II sample introduction systems.

Evaluation of a new sector-field ICP-MS with Jet Interface for ultra-trace

J. Nucl. Radiochem. Sci., Vol. 15, No. 1, 2015

9

TABLE 1: Instrument and data acquisition settings for SF-ICP-MS (Element XR) and the sample introduction systems(APEX-Q and Aridus II)
SF-ICP-MS
Instrument settings
Forward power
Nebulizer
Sample cone
Skimmer cone
TorchCool gas
Auxiliary gas
Sample gas (nebulizer gas)
Data acquisition settings
Low resolution (m/Δm = 300):
Acquisition mode
Monitored mass (m/z)
No. of scans (runs x passes)
Mass window
Samples per peakSample time
Integration type
Total time of analysis
APEX-Q settings
Sample uptake rate
Spray chamber temperature
Condenser temperature
Sweep gas (Ar)
Additional gas (Ar)N2 gasAridus II settings
Sample uptake rate
Spray chamber temperature
Membrane oven temperature
Sweep gas (Ar)N2 gas1200 W
Conical concentric and PFA Aspire
Nickel, 1.1 mm orifice diameter
Nickel, 0.8 mm orifice diameter or X-cone with Jet Interface
Fassel16 L min-1
0.85 L min-1
0.97-1.00 L min-1 (optimized daily to highest intensity of 238U+ and lowest possibleoxide formation rate)

E-scan (peak jumping)
238, 239, 240, 241, 242
20 × 410 %100
10 ms for 238U+; 30 ms for 242Pu+; 70 ms for 239Pu+; and 100 ms for 240Pu+ and 241Pu+
Average
150 s
0.2 mL min-1 (with conical nebulizer)
140 °C
2 °C
3 L min-1
0.1 L min-1
8~10 mL min-1
0.05 mL min-1 (with PFA Aspire nebulizer)
110 °C
160 °C
6.5 L min-1~ 5 mL min-1

improvement can be gotten by introducing N2 gas into the
APEX-Q. For Pu analysis, the sensitivity enhancement was notdue to the effect of charge transfer with Pu atom resulting inionization of Pu. Considering the quite low first ionization
potential of Pu (6.03 eV), Pu tends to be almost completely
ionized in the hot plasma, the sensitivity improvement is most
likely a result of minimizing PuO formation [21]. For cleanup
after use, the ACM desolvation module is easily removed fromthe APEX, and cleaned using an acidic solution.
The Aridus II desolvation system is also widely used for
ultra-trace radionuclide measurement. It consists of a self-aspiration nebulizer, the Aspire PFA nebulizer, equipped on theheated PFA spray chamber which is connected to column withthe heated fluoropolymer membrane. The nebulizer sprays
sample solution into the heated PFA spray chamber; the hightemperature (up to 110 °C) maintains the sample in the vapor
phase. The sample vapor then enters the heated PTFE membrane desolvator module. Similar to the APEX-Q system, acountercurrent flow of Ar sweep gas is introduced to remove
solvent vapors that permeate the membrane wall. Nonvolatilesample components do not pass through the membrane wall;
instead they continue to the SF-ICP-MS torch injector where
they are ionized in the plasma. The difference between the
APEX-Q and the Aridus II is that in the latter, the sample mistfrom the heated spray chamber is immediately transported tothe membrane desolvation module without passing through acondenser to cool it down. The desolvation module can be easily removed for cleaning. Three different nebulizers can beused to achieve sample uptake rates of 50, 100, or 200 μL min-1.

2.3. Analytical procedure for determination of Pu isotopes in sediment and seaweed reference materials. Two
reference materials, NIST-4357 (ocean sediment) and IAEA446 (seaweed), were used to test the applicability of the new
SF-ICP-MS for the determination of Pu isotopes in environmental samples. For NIST- 4357, ca. 0.5 g ashed (450 °C, 4 h)samples were digested with HNO3 -HF after adding 0.57 pg
242
Pu tracer. The samples were then evaporated to dryness, followed by adding 3 mL HClO4. Next, 3 mL conc. HNO3 wasadded and the solution was evaporated to dryness, this step was
repeated twice. The residue was dissolved in 50 mL 1 M
HNO3 , and 4 mg Fe3+ was added as carrier. Then, 2.5 mL
NH2OH·HCl (80 g L-1) was added to change Pu to Pu(III) and
Pu was further co-precipitated with Fe(OH)3. The precipitate
was dissolved in 1.5 mL conc. HNO3 and then 50 mL 8 M
HNO3 was added to the solution along with 0.4 g NaNO2 toadjust oxidation state of Pu to Pu (IV). For IAEA-446, a nitricacid leaching method was used to release Pu. In brief, 3-8 g
seaweed samples were ashed at 450 °C for 4 h, then, samples
were transferred to a capped 120 mL Teflon vessel. After adding 20 mL conc. HNO3, samples were digested at 160˚C for
4 h. After filtration and adjusting the acidity to 8 M HNO3,
0.41g NaNO 2 was added to take Pu to the tetravalent state.
After acid leaching or digestion, samples were subject to thesubsequent two-stage anion chromatographic chemical separation as described by Bu et al. [22]. Briefly, Pu was separated
from sample matrix using an AG 1X8 anion-exchange column.
The obtained Pu fraction was further purified using an AG
MP-1 M anion-exchange column with HBr for Pu elution.
After removing any trace of HBr, the sample was finally dis-

10

Zheng

J. Nucl. Radiochem. Sci., Vol. 15, No. 1, 2015

solved in 4% HNO3, in preparation for the SF-ICP-MS analysis.
For Pu isotope ratio measurements, a Pu isotopic standard(NBS 947) was used with sample-standard bracketing to correct externally for instrumental mass bias. Details of the mass
bias correction have been described in previous work [18].

Aridus II/SF-ICP-MS

3. Results and Discussion
In the present evaluation study on determination of Pu isotopes, the SF-ICP-MS (Element XR) equipped with the Jet
Interface was used in the low resolution mode in order to utilize the maximum instrument sensitivity. Additionally, thenormal skimmer cone was replaced by a high-efficiency cone
(X-cone, Thermo Scientific) for further increasing sensitivityof the SF-ICP-MS. All the measurements were made in the
self-aspirating mode to reduce the risk of contamination by theperistaltic pump tubing. The SF-ICP-MS was optimized dailyusing a 0.1 ng mL-1 U standard solution (Merck multi element
standard) when using the standard sample introduction system
consisting of a concentric nebulizer (50 μL min -1 sample
uptake) and a Scott-type double-pass spray chamber, and 0.02
ng mL -1 U standard solution when using the high efficiency
sample introduction systems (APEX-Q and Aridus II).
Optimized instrument conditions for the determination of Pu
isotopes are listed in Table 1.
3.1. Sensitivity and detection limit for Pu analysis. Figure
2 compares the background levels (cps) in the Pu isotope mass
region (m/z 238-242) using the APEX-Q and Aridus II sample
introduction systems. Diluted nitric acid (4%) was analyzed
for this background evaluation. Both systems had similarly
low background (ca. 2 cps) in the Pu isotope mass region. For
these two sample introduction systems, the sensitivity of Pu
analysis was estimated using the Pu isotope standard solution(NBS 947) at concentrations of 10 and 100 fg mL -1. The
obtained mass spectra are shown in Figure 3. For the Element
XR SF-ICP-MS without the Jet Interface (Figure 3A), the signal intensity of 100 fg mL-1 239Pu was ca. 350 cps; significant
sensitivity improvement was obtained both for the Aridus II/
SF-ICP-MS (with Jet Interface) (Figure 3B) and APEX-Q/SFICP-MS (with Jet Interface) (Figure 3C). For 100 fg mL -1
239
Pu, the signal intensity obtained with the Aridus II/SF-ICPMS was 10,000 cps, corresponding to a sensitivity of 100
Mcps/ppb (ppb = ng mL -1). For 10 fg mL -1 239Pu, the signal
intensity obtained with the APEX-Q/SF-ICP-MS was 600 cps,
corresponding to a sensitivity of 60Mcps/ppb. These results
indicated that compared to the SF-ICP-MS without the Jet
Interface, the combination of the APEX-Q or Aridus II sample
introduction system with Jet Interface resulted in ca. 20-, or
30-fold sensitivity improvement. The higher sensitivity of the
Aridus II system indicated its better desolvation ability.
However, it was observed that washing out of the remaining
signals of the APEX-Q system was faster than for the Aridus
II. This was probably caused by the buildup of analyte andsample matrix on the inner wall of the heated PFA spray chamber of the Aridus II system, which would cause signal spikes
and longer sample washout time.
Since the highest sensitivity was obtained with the Aridus
II/SF-ICP-MS (with Jet Interface) system, the detection limit
was estimated based on the definition of 3 times the standard
deviation of blank (4 % HNO3). An extremely low detection
limit of 0.043 fg mL -1 was achieved for Pu isotope analysis.
Taking into account the low sample uptake rate (0.05 mL min-1)
using the PFA nebulizer and the short time for analysis (150 s)(cf. Table 1), a sample solution of only 0.125 mL would be
required for Pu isotope analysis, thus an absolute detection
limit of 5 attogram (or 1.3×10 4 atoms) could be calculated.
This detection limit was about one order of magnitude lower
than the detection limit obtained with the APEX-Q/SF-ICP-

APEX-Q/SF-ICP-MS

Figure 2. Background levels (cps) of Element XR coupled to the
APEX-Q and Aridus II; estimated using 4 % HNO3.

A. Element XR without Jet Interface
50μl/min nebulizer
NBS 947 100 ppq 239Pu

Sensitivity: 3.5 Mcps/ppb

B. Element XR, Jet Interface, with Aridus II
50μl/min nebulizer
NBS 947 100 ppq 239Pu

Sensitivity: 100 Mcps/ppb

C. Element XR, Jet Interface, with APEX-Q
100μl/min nebulizer
NBS 947 10 ppq 239Pu

Sensitivity: 60 Mcps/ppb

Figure 3. Mass spectra of NBS 947 standard solution obtainedusing: (A) the Element XR without the Jet Interface; (B) the Aridus
II/Element XR with the Jet Interface; and (C) the APEX-Q/Element
XR with the Jet Interface.

MS (Element 2) [18], pushing the detection of Pu isotope fromthe femtogram down to the attogram levels. So far, AMS has
been widely recognized as the technique providing the highestEvaluation of a new sector-field ICP-MS with Jet Interface for ultra-trace

J. Nucl. Radiochem. Sci., Vol. 15, No. 1, 2015

11

TABLE 2: Comparison of the interference effect from 238UH + on the determination of 239Pu by SF-ICP-MS with different
sample introduction systems
Sample introduction system

UH+/U+

References

Pneumatic nebulizer
MCN-100
MicroMist
Q-DIHEN
USN-5000 +USN+MINI-GASS
MCN-6000
Aridus
APEX-Q with ACM unit
APEX-Q with ACM unit
(Element XR-Jet Interface)
Aridus II(Element XR-Jet Interface)

7.59 – 8.39 × 10 -5
4.05 – 4.73 × 10 -5
1.8 × 10 -4
1 – 5 × 10 -4
3.20 – 4.00 × 10 -5
2.33 – 2.79 × 10 -5
1.35 – 1.80 × 10 -5
3.2 × 10 -5
1.16 – 1.95 × 10 -5
2.0 × 10 -5

27
27
28
28
27, 2827
27
28
18This study

2.2 × 10 -5This study

TABLE 3: Precision and accuracy of ultra-trace Pu isotope analysis using Aridus II/SF-ICP-MS with a single measurement(runs × passes 20 × 4)
240

Analytical system
AB

Pu/239Pu atom ratio
Measured
Certified
0.234±0.048
0.242
0.242
0.240±0.012

239

Pu conc. (fg mL-1)

Precision (RSD %)Accuracy (%)

100
100

20.5
5.0

-3.3
0.83

A: Element XR without Jet Interface.
B: Aridus II/SF-ICP-MS with Jet Interface.

sensitivity for ultra-trace Pu isotope analysis [23], and thereported detection limit has ranged from 104 to 106 atoms [2326]. Therefore, the detection limit obtained with the Aridus
II/SF-ICP-MS (with Jet Interface) system is definitely comparable to or even better than the AMS detection limit.
3.2. Effect of UH + interference. The presence of uranium
in environmental samples may hamper the accurate determination of Pu isotopes, especially for 239Pu, due to uranium hydrideion formation (238UH +) and the peak tailing effect from 238U+.
The sample introduction system is recognized as the mostimportant factor affecting formation of uranium hydride ionsin a plasma compared with other factors, such as gas flow rate,
and the distance of the torch from the cone [18]. Then a 0.1 ng
mL-1 U standard solution was used to evaluate the 238UH + formation rate in the APEX-Q and Aridus II systems and it was
ca. 2 × 10 -5 (Table 2). This rate was similar to that for the
APEX-Q/Element 2 system [18], indicating that the Jet interface equipped in the Element XR did not increase the 238UH +formation although a Jet sampler cone with larger orifice diameter was used. Kim et al. have investigated the influence of theinterference effect of 238U at 239 m/z with various sample introduction systems, and found that the MCN-6000 microconcentric nebulizer coupled with the membrane desolvation systemshowed the lowest hydride formation [27], while the MicroMist
and Q-DiHEN systems showed a much higher interference
effect from the formation of 238UH+ [28]. As shown in Table 2,
the 238 UH + formation rate obtained with the APEX-Q and
Aridus II systems in Element XR was comparable with that of
the MCN-6000 sample introduction system, and was among
the lowest values reported in the literature. In previous studies,
the author and co-workers developed a highly effective chemical separation method for Pu determination in environmental
samples with extremely high U decontamination factor (106 forsoil and sediment, 107-108 for seawater) [22,29]. Therefore, theinfluences of uranium hydride molecular ions, as well as thepeak tailing effect from 238U were considered negligible for thedetermination of Pu isotopes in environmental samples whencombining the highly sensitive SF-ICP-MS with the developedchemical separation methods.
3.3. Precision and accuracy of Pu isotope ratio measurement. The precision (RSD %) and accuracy of Pu isotope
analysis using the Aridus II/SF-ICP-MS (with Jet Interface)system were estimated by a single measurement (runs × passes
20 × 4) of 100 fg mL -1 239Pu (NBS 947 Pu isotope standard
solution), and compared with the values obtained with the
Element XR without using the Jet Interface (Table 3). The
Element XR without the Jet Interface gave a precision of the240
Pu/ 239Pu atom ratio of 20.5 % and accuracy of -3.3 %, and
the Aridus II/SF-ICP-MS (with Jet Interface) gave a precisionof 5.0 % and accuracy of 0.83 %; both precision and accuracy
were significantly improved for the latter.
Figure 4 shows the effect of Pu concentrations (239Pu and240Pu) on the precision, based on a single measurement (runs ×
passes 20 × 4) using the APEX-Q/SF-ICP-MS (Element XR).
The concentrations of Pu investigated were 1, 5, 10, 20, 50 and
110 fg mL-1 for 239Pu and 0.24, 1.21, 2.65, 4.82, 12.1 and 26.5 fg
mL -1 for 240Pu. For 240Pu/ 239Pu atom ratio, the RSD % varied
from 7 % to 45 %, it decreased with Pu concentration increase.
Better RSD % values lower than 10 % could be obtained when240
Pu was higher than 4.82 fg mL-1.
It is necessary to check how reliable the isotopic ratio measurement with the instrument for a long-term. Thus the longterm stability of the SF-ICP-MS (Element XR) for thedetermination of 240Pu/ 239Pu atom ratio at ultra-trace level was
estimated from April to December 2014, an 8-month period,
using the APEX-Q/SF-ICP-MS system with NBS 947 at a concentration level of 11 fg mL -1 239Pu and 2.7 fg mL -1 240Pu. As
shown in Figure 5, during eight months, the variation of thedetected 240 Pu/ 239Pu atom ratios was within ±1σ, indicating
excellent long-term stability for ultra-trace level Pu isotope
analysis.
3.4. Determination of Pu isotopes in sediment and seaweed reference materials. Two standard reference materials,

ZhengJ. Nucl. Radiochem. Sci., Vol. 15, No. 1, 2015
240

0

5

0.300

Pu concentration (fg mL-1)
10

15

20

25

Pu/239Pu atom ratio

40

30

240

RSD of 240Pu/239Pu atom ratio (%)

50

0.280
0.260
0.240


0.220

10

Figure 5. Long-term (8 month) stability of the APEX-Q/SF-ICP-MS(Element XR) for the determination of 240 Pu/ 239Pu atom ratios of
NBS-947 (11 fg mL-1 239Pu and 2.7 fg mL-1 240Pu).

0
0

20

40
239

60

80

100

Mean = 0.246 ± 0.009
Certified 0.242

0.200
0.180

20


mean

201
4/A
201 pril/1
0
4/A
pril
/10
201
4/A
pril
/16
201
4/J
une
/02
201
4/J
une
/13
201
4/J
une
/23
201
4/J
uly
/
201
02
4/J
uly
/10
201
4/J
uly
/17
201
4/A
ug.
/05
201
4/N
ov.
/19
201
4/D
ec./
02

12

120

Pu concentration (fg mL-1)

Figure 4. Relative standard deviation (RSD %) for the 240Pu/ 239Pu
atom ratio in NBS-947 measured by the APEX-Q/SF-ICP-MS plottedagainst 239Pu and 240Pu concentrations.

ity of 241Pu were 0.238 ± 0.002, 0.0130 ± 0.0006, and 124.1 ±14.9 mBq g-1, respectively, which were comparable with the literature values. These results demonstrated the applicability of
the new SF-ICP-MS equipped with the Jet Interface for ultratrace determination of Pu isotopes in environmental samples.
Currently, this new analytical system has been applied to thedetermination of Pu isotopes in various environmental samples, such as sediment, seawater, soil and agricultural crops forradiological impact assessment following the Fukushima
Daiichi Nuclear Power Plant accident.

NIST-4357 ocean sediment and IAEA-446 seaweed were analyzed for Pu isotopes. The results we obtained are comparedwith the certified and previously reported values [22, 30-33].
Table 4 summarized the analytical results of activities of
239 +240
Pu and 241 Pu, and atom ratios of 240 Pu / 239 Pu and241
239
Pu/ Pu. As can be seen, the mean 239+249Pu activities for
NIST-4357 (n = 5) and IAEA-446 (n = 3) were 10.82 ± 1.39
and 0.026 ± 0.001 mBq g-1, respectively, agreed well with thecertified values. In addition, for IAEA-446, the mean (n = 3)
of 240Pu/ 239Pu atom ratio was 0.222 ± 0.003, also agreed wellwith the certified value of 0.220 ± 0.006 [33]. For NIST-4357,
we also measured 241Pu activity and 241Pu/ 239Pu atom ratio.
Although the atom ratios of 240Pu/239Pu and 241Pu/239Pu, and theactivity of 241Pu were not certified for NIST-4357, they werereported in the literature [22, 30-33]. In this study, the mean(n = 5) atom ratios of 240Pu/239Pu and 241Pu/239Pu, and the activ-

4. Conclusions
In this study a detail evaluation was made on the analyticalpotential of a new SF-ICP-MS equipped with the Jet Interface
for ultra-trace determination of Pu isotopes. In order to further
improve the sensitivity for Pu isotope analysis, high efficiency
sample introduction systems (APEX-Q and Aridus II) werecombined with the new SF-ICP-MS. A certified Pu isotope
standard solution (NBS-947) and a U standard solution (Merck

TABLE 4: Results of reference materials measured in this study using APEX-Q/SF-ICP-MS and the certified and information values
239+240

Pu activity(mBq g-1) a

SampleAmount (g)NIST-4357 1
NIST-4357 2
NIST-4357 3
NIST-4357 4
NIST-4357 5mean (n=5) b

0.538
0.525
0.530
0.619
0.608

9.36±0.48
12.34±0.93
10.24±0.70
9.87±0.44
12.26±0.30
10.82±1.39

IAEA-446 1
7.813
IAEA-446 2
3.829
IAEA-446 3
3.267
mean (n=3) b
Certified/information values
NIST-4357
IAEA-446

0.025±0.003
0.026±0.005
0.027±0.005
0.026±0.001a9.2-13.3
0.022-0.026

Pu activity(mBq g-1) a,c

Pu/ 239Pu
atom ratioa

Pu/ 239Pu
atom ratioa,c115.6±11.6139.8±16.4
115.1±15.1
109.3±9.3140.6±13.9124.1±14.9

0.239±0.009
0.238±0.005
0.241±0.008
0.236±0.008
0.238±0.008
0.238±0.002

0.0140±0.0045
0.0129±0.0036
0.0128±0.0050
0.0125±0.0042
0.0128±0.0040
0.0130±0.0006

241

240

241

0.219±0.028
0.222±0.041
0.225±0.048
0.222±0.003
119.5±13.3d

0.233-0.244e
0.220±0.006g

0.0132±0.0007f

Uncertainties represent 1σ error; bAverage of the measured replicates ± standard deviation.c Decay of 241Pu corrected to 1 Jan.
2000; dData cited from Bu et al. [22]; eData cited from Hrnecek et al. [30 ] and Yoshida et al. [31]; f Data cited from Zhang et al.
[32]; gData cited from Pham et al. [33].

Evaluation of a new sector-field ICP-MS with Jet Interface for ultra-trace

multi element standard) were used to investigate four items: theformation rate of 238UH+, which could interfere with ultra-tracelevel 239Pu determination; the detection limit for Pu; the precision and accuracy for 240Pu/239Pu atom ratio determination; andthe long-term (8-month) stability for Pu isotope composition
analysis. For a single measurement (runs × passes 20 × 4), theprecision of the 240Pu/ 239Pu atom ratio lower than 10 % could
be obtained with a concentration level of 11 fg mL-1 239Pu and
2.7 fg mL-1 240Pu. Due to the exceptional sensitivity of the new
SF-ICP-MS, a detection limit at the attogram (10 -18 g) level wasachieved, which was comparable or even surpass that of AMS.
Acknowledgements
The author wishes to acknowledge Dr. K. Tagami, Dr. S.
Uchida, Dr. Z. T. Wang, Mr. W. T. Bu and Mr. L. G. Cao for
their useful discussion and constructive suggestions. This work
was supported by the Agency for Natural Resources andEnergy (METI), Japan.
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