Journal of Nuclear and Radiochemical Sciences, Vol. 20, pp. 12-19, 2020

ArticlesAccurate determination of three halogen elements (Cl, Br, and I) in U.S. Geological Survey
geochemical reference materials by radiochemical neutron activation analysis and an
exhaustive comparison with literature data: a review
Shun Sekimotoa,* and Mitsuru EbiharabaInstitute for Integrated Radiation and Nuclear Science, Kyoto University, 2-1010 Asashiro-nishi, Kumatori, Sennan, Osaka 590-0494, Japanb
School of Education, Waseda University, 1-104 Totsukamachi, Shinjuku-ku, Tokyo 169-8050, Japan
Received December 4, 2018; Accepted December 27, 2019; Published online February 5, 2020
Since trace amounts of three halogens (chlorine, bromine, and iodine) in 17 U.S. Geological Survey (USGS) geochemical reference materials were recently determined using radiochemical neutron activation analysis (RNAA)
by the authors, the RNAA data of the three halogens were exhaustively compared with corresponding literature
data and some inconsistencies were found. Those inconsistencies can be explained by the loss of iodine in pretreatment of the solution that is subjected to inductively coupled plasma mass spectrometry (ICPMS), incompletequantitative collection of chlorine in pyrohydrolysis preconcentration for ICPMS, and overestimation due to theinterference in the ICP double focusing sector field MS (ICPSFMS) instrument. Using the relative standard deviation (RSD) that accompanies the mean value in each USGS material, homogeneity of halogens in the USGS
materials has been discussed.

1. Introduction
When determining the elemental composition of geochemical and cosmochemical samples, it is usual to search for any
scientific implications related to those samples by consulting
chemical, geochemical and cosmochemical properties of theelements of interest. For halogens, their chemical properties
have been extensively studied and are known to vary from element to element. However, geochemical and cosmochemical
properties of halogens are poorly understood because accurate
and reliable data for halogen abundance have been rarely
reported for samples such as crustal rock, mantle material andmeteorites. Iodine, among the halogens, is the most informative element in discussion of the geochemical circulation ofcrustal material because geochemists often discuss the geochemical circulation of iodine in the earth’s surface, oceanic
crust, continental crust, and mantle.1 Iodine is also of highimportance and of particular interest for cosmochemists when
they discuss the cosmochemical behavior of its extinct nuclide129
I (half-life of 15.7 million years) in the early solar system.
Since halogens differ in volatility from element to element,
their content and relative abundance are highly informative
when discussing the petrogenesis of samples.2 Thus the scarcity of reliable data for geochemical and cosmochemical samples hinders the geochemical and cosmochemical discussion of
halogens.
There are few accurate and reliable data of halogens in terrestrial rock samples, as can be witnessed in the data libraryfor geological rock samples prepared by United States
Geological Survey (USGS) (at http://crustal.usgs.gov/geochemical_reference_standards/powdered_RM.html). Various
kinds of rocks within the database are recorded with only
information values or a few recommended values for halogen
concentration, but for most of the rocks no values are listed.
This deficit is probably related to difficulties in determining
trace amounts of halogens within these samples. Recently wehave improved the radiochemical neutron activation analysis*Corresponding author. E-mail: sekimoto@rri.kyoto-u.ac.jp, Fax:
+81-72-451-2622(RNAA) procedure for trace amounts of halogens (chlorine,
bromine and iodine) and have demonstrated that our RNAA
data for Br and I are more reliable and accurate than the dataobtained by inductively coupled plasma mass spectrometry(ICPMS) coupled with pyrohydrolysis preconcentration. 3
Then, our RNAA procedure was applied to 17 USGS geochemical reference materials and trace concentrations of threehalogens (chlorine, bromine and iodine) were determined.4 As
some of the 17 reference materials have literature values for
halogens, our RNAA values were exhaustively compared withthose literature values. From the comparison, the consistencyof the two data sets was evaluated and the causes of inconsistency between them were investigated. In addition, the homogeneity of each reference material was discussed, based on therelative standard deviation (RSD) that accompanies the meanvalue in each reference material.
2. Procedure of RNAA
2.1. Sample preparation. The 17 USGS geochemical reference materials are listed in Table 1, together with additional
information. The materials were all obtained commercially.
All the materials were in powder and were not subjected to any
additional treatment such as drying. About 20-300 mg of eachpowder sample was weighed, inserted into a clean, small plastic vial that was sealed and then re-sealed inside a clean polyethylene bag. Chemical standard solutions of the threehalogens of interest were prepared for use in the quantification
by RNAA. An appropriate amount of each halogen solution(containing 90 μg of chlorine, 50 μg of bromine, and 10 μg of
iodine) was dropped onto a paper disk (17 mm diameter,
ADVANTEC, Filter Paper No.7), weighed, dried under a heatlamp and doubly sealed into polyethylene bags. Extreme care
was taken to prevent loss of iodine when preparing the iodinereference sample.5, 6 Halogen standard solutions were preparedby dissolution of KCl (99.9% Wako Pure Chemical Industries,
Ltd., hereafter Wako Chemical), KBr (99.9% Wako Chemical),and KI (reagent special grade Wako Chemical) for Cl, Br, andI respectively.

© 2020 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 02/05/2020

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Sekimoto

TABLE 1: USGS geochemical reference materials analyzed by RNAA
Sample code

sample typesampling location

BHVO-2
BCR-2
BIR-1aW-2a
AGV-2
DNC-1aGSP-2
DTS-2bQLO-1a
COQ-1
CLB-1
SDC-1
Nod-P-1
Nod-A-1
SBC-1
SGR-1b
DGPM-1

basaltbasaltbasaltdiabaseandesitedoleritegranodiorite
dunitequartz latite
carbonatite
coal
mica schist
manganese nodule
manganese nodulemarine shale
shale rockdisseminated gold ore

pahoehoe lava, the Halemaumau crater, Hawaii, USA
Bridal Veil Flow Quarry, Oregon, USAinterglacial lava flows, Reykjavik, Iceland
the Bull Run quarry, Centreville, Virginia, USAeastern side of Guano Valley, Lake County, Oregon, USA
Braggtown quarry, North Carolina, USA
Silver Plume quarry, Colorado, USA
Twin Sisters Range, Washington, USA
Lake County, Oregon, USA
Oka complex, Montreal, Canada
Lower Bakerstown coal bed, Maryland, USA
Washington D.C. area, USA
Pacific Ocean (14° 50’ N, 124° 28’ W)
Atlantic Ocean (31° 02’ N, 78° 22’ W)
Westmoreland County, Pennsylvania, USA
Green River, Wyoming, USA
Pinson mine, Nevada, USA

TABLE 2: Nuclear data of radioactive nuclides concerned in RNAA
Element Target nuclides
Cl
35Br
53I
17

37

Cl
Br
127
I

81

Isotopic abundance(%)

Cross sectiona(barn)

24.24
49.31
100

0.43
2.64
6.2

Produced nuclideb
38

Cl
Br
128
I

82

Half life

γ-ray energyc(keV)

37.18 m35.34 h25.0 m

1642, 2168
776, 554
443

a

Neutron capture cross-section for thermal neutrons.
Produced by neutron capture reaction.
c
Used in gamma-ray spectrometry for quantification of elements.
b

2.2. Neutron irradiation. Two USGS materials, together
with a set of three reference halogen samples, were irradiatedfor 10 min with a thermal neutron flux of 3.3 × 1012 cm-2 s-1 at
Kyoto University Research Reactor Institute (KURRI), withthe exception that a 1 min irradiation was used in the one
experimental run for the Manganese Nodule sample (Nod-P1). When a high f lux reactor is used, samples need to becooled to prevent iodine loss,7 however no such cooling was
required with the neutron flux used in our previous study.4
After irradiation, the USGS materials were held for a few minutes to enable the decay of 28Al, and were then subjected toradiochemical separation of neutron-activated halogen radionuclides (38Cl, 82Br, and 128I).
2.3. Radiochemical purification procedure, gamma ray
measurement and yield determination in RNAA. The procedure of radiochemical purification for halogens, gamma-ray
measurement and yield determination was essentially the sameas that described in our previous work3 and is briefly outlined
here. An irradiated reference material is transferred to thenickel crucible, which contains a known amount of each halogen carrier and a manganese carrier, and is fused with NaOH.
The fused cake is digested in water and the hydroxide precipitate is separated from the supernatant. A few mg of sodium
sulfite (solid) is then added to the supernatant solution containing the halogens in order to prevent the loss of iodine andfacilitate the neutralization of the supernatant in the next step.
From the supernatant, which is made slightly acidic by adding
6M HNO3, an initial precipitate of PdI 2 is formed by adding

Pd(NO3)2 solution. Then a mixture of AgCl+AgBr precipitates
is formed by adding AgNO3 solution to the supernatant containing chlorine and bromine. The PdI 2 and the mixture of
AgCl+AgBr precipitates are washed with a sufficient amountof 0.2M HNO3. Those precipitates are subjected to gammaray counting with a Ge semiconductor detector (ORTEC
GEM-50195). The use of the manganese carrier, the additionof sodium sulfite as a solid and the washing by 0.2M HNO3
improve the analytical sensitivity in this RNAA procedure andthe effects are described elsewhere in detail.3 The reagentsused here were of reagent special grade (Wako Chemical).
For the determination of iodine and chlorine, the radioactivity of 128I and 38Cl was measured by using a Ge detector for
300–1,000 s and 500–1,000 s, respectively. For bromine, 82Br
was measured for 50,000–100,000 s on the following few days
after the radiochemical procedure. The three halogen reference samples were measured individually after the completionof the measurements, for for 200-500 s for Cl and I, and
1,000–2,000 s for Br.
Chemical yields of the three halogens were determined by
the reactivation method. After the completion of all gammaray measurements, a set of 4-6 samples (either of PdI 2 or
AgBr+AgCl mixture), along with reference samples for thecorresponding halogens, were irradiated for 10 sec at the same
irradiation facility as used earlier. The radioactivity of 38Cl,
82
Br, and 128I was measured for 100 s for each nuclide. The
nuclear data related to the NAA of the halogens are summarized in Table 2.

Accurate determination of three halogen elements (Cl, Br, and I) in U.S.

3. Results and Discussion
3.1. Cl, Br, and I contents in USGS reference materials.
Each material was analyzed two to four times (individual values are tabulated in Appendix). For seven USGS materials
which were analyzed twice, the two analytical values for thethree halogens are in agreement within uncertainties, andmean values between those two analytical values are summarized in Table 3. An uncertainty quoted for each mean value
between two analytical values is just the value calculated from
two individual uncertainty values accompanied by the twoanalytical values. Since ten USGS materials besides the sevendescribed above have three or four analytical values for thethree halogens, mean values with one sigma of standard deviation for those ten materials are also summarized in Table 3,with the exception that the bromine value in BCR-2 is themean of two analytical values. The chlorine and bromine contents vary from 5.64 mg kg-1 for BIR-1a (basalt) to 4,410 mg
kg-1 for Nod-A-1 (manganese nodule), and from 0.039 mg kg-1
for BIR-1a (basalt) to 52.1 mg kg-1 for CLB-1 (coal), respectively. The iodine content varies from 0.041 mg kg -1 forBIR-1a (basalt) to 599 mg kg-1 for CLB-1 (coal). The variationis thus over two, three and four orders of magnitude for chlo-

J. Nucl. Radiochem. Sci., Vol. 20, 2020

rine, bromine and iodine, respectively, confirming that the
RNAA procedure applied in our previous study4 has a muchlarger dynamic range in determining the three halogens ingeochemical powder materials.
When the two shale samples (SBC-1 and SGR-1b) werefused with NaOH in radiochemical purification for halogens, aflame was sometimes found in nickel crucible. Since thoseshale materials have organic form of carbon, the flame musthave been derived by the combustion of organic compounds
included in those shale materials. The two samples wererepeatedly analyzed (3 and 2 times for SBC-1 and SGR-1a,
respectively) and reasonable agreements were confirmed
among duplicate data for individual halogens. Probably, thesamples ignited after being melted with NaOH and the equilibrium between neutron-capturing radioactive nuclides and stable nuclides was established among individual halogens.
Nevertheless, since a possibility of loss of stable halogens
before isotopic equilibration cannot be denied, it may be safe
to regard our data as lower limits.
The drying instructions for the manganese nodule samples(Nod-P-1 and Nod-A-1), indicate that they can absorb up to
10% by weight of moisture when exposed to air overnight. As
already mentioned, those samples were not dried before

TABLE 3: Cl, Br and I Content in USGS Geochemical Reference Materials Analyzed by RNAAa and from the
Literature
SampleDTS-2b
COQ-1
CLB-1
SBC-1
DGPM-1
W-2a
SGR-1b
DNC-1aDNC-1

QLO-1a

SDC-1

GSP-2

BHVO-2RNAA (n = 3)
RNAA (n = 2)
RNAA (n = 4)
RNAA (n = 3)
RNAA (n = 2)
RNAA (n = 4)
Certificate of Analysis
RNAA (n = 2)
Certificate of Analysis
RNAA (n = 4)
INAA10Compiled8
Certificate of Analysis
XRF9
RNAA (n = 3)
Compiled8
Certificate of Analysis
INAA10RNAA (n = 2)
Compiled8
INAA10
Certificate of Analysis
RNAA (n = 3)
Noble gas18
various methods11
RNAA (n = 2)
IC12
ICPMS12IC13ICPMS13
IC14
IC17
Noble gas18

14

Cl (mg kg-1)

Br (mg kg-1)

I (mg kg-1)

10.7 ± 0.3
27.5 ± 1.1
1190 ± 150
24.9 ± 2.4 b
315 ± 12220 ± 22190 c
22.0 ± 1.0 b
32 c
18.1 ± 3.2
-d
37 e
60 c
60 ± 4244 ± 16219e
220 ± 18e-d30.0 ± 1.4
32 e
-d
32 c
363 ± 29381 ± 29400 ± 10104 ± 4150 ± 21-d
81 ± 11-d
89 ± 784 ± 5102 ± 1

0.093 ± 0.002
0.071 ± 0.006
52.1 ± 6.8
0.355 ± 0.005 b
0.843 ± 0.033
0.309 ± 0.040-d0.409 ± 0.020 b-d0.063 ± 0.013
<0.5
-d
-d
-d
1.03 ± 0.05
2.07 c2.1 c
1.08 ± 0.11
0.111 ± 0.011
0.097 c<0.5
-d0.117 ± 0.020
0.077 ± 0.023-d0.240 ± 0.013-d0.269, 0.277-d0.29 ± 0.10-d-d0.259 ± 0.005

0.789 ± 0.148
0.331 ± 0.094
599 ± 52
5.07 ± 0.19 b
3.55 ± 0.13
0.405 ± 0.071-d2.16 ± 0.15 b-d0.102 ± 0.018
-d
-d
-d
-d
0.741 ± 0.088-d-d-d
0.187 ± 0.034-d-d-d
0.075 ± 0.018
0.020 ± 0.006-d0.307 ± 0.050-d0.016 ± 0.002-d0.020 ± 0.012-d-d0.070 ± 0.004

J. Nucl. Radiochem. Sci., Vol. 20, 202015

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TABLE 3: Cl, Br and I Content in USGS Geochemical Reference Materials Analyzed by RNAAa and from the
Literature (Continued)
Sample
BCR-2

BIR-1a
BIR-1

AGV-2

Nod-P-1
Nod-A-1

RNAA (n = 3)
IC12
ICPMS12
IC14
IC17
XRF15
Noble gas18
RNAA (n = 4)
Noble gas18
IC12
IC17
ICPMS12INAA10Compiled8
Certificate of Analysis
RNAA (n = 2)
IC12
ICPMS12
IC14
Noble gas18
RNAA (n = 4)
ICPSFMS16RNAA (n = 2)
ICPSFMS16

Cl (mg kg-1)

Br (mg kg-1)

I (mg kg-1)

112 ± 198 ± 8-d
89 ± 694 ± 4101
106.4 ± 0.3
5.64 ± 0.431144
5.7 ± 0.3
-d
-d
26g
26c
72.8 ± 2.7
75 ± 3-d
61 ± 3831380 ± 140-d4410 ± 160-d0.144 ± 0.008f-d0.157, 0.175-d-d-d0.192 ± 0.022
0.039 ± 0.012
0.037
-d
-d
0.065 ± 0.026<2-d-d
0.101 ± 0.007-d0.107, 0.145-d
0.244
5.93 ± 0.76
30.3 ± 2.2
14.8 ± 0.5
40.9 ± 0.7

0.082 ± 0.022-d0.017 ± 0.004-d-d-d
0.058 ± 0.002
0.041 ± 0.009
0.007
-d
-d
0.014 ± 0.002-d-d-d
0.197 ± 0.038-d0.007 ± 0.001-d0.080
157 ± 1731.4 ± 0.3
367 ± 947.7 ± 3.2

aMean values followed by standard deviations (1σ) (n=3, 4). Mean values followed by an uncertainty which is simply thevalue calculated from two individual uncertainty values (n=2).
b
It may be safe to regard RNAA data as lower limits (see text for details).
c
Information values.
d
Not reported.
e
Recommended valuesfn=2.
g
Proposed values.

RNAA because they are usually stored in a desiccator. If
those samples absorbed up to 10% by weight of moisture priorto RNAA, it would be safe to enhance our concentration databy a factor of 1.1 to compensate for moisture.
In Table 3, our data are compared with the values in the literature,8-18 although the data usable for the comparison of ourdata are still limited in number, as is evident in Table 3.
Literature values for chlorine include the data obtained by ion
chromatography (IC) or x-ray fluorescence analysis (XRF)
and compiled data such as information, recommended andproposed values, whereas those for bromine include the dataobtained by ICPMS or instrumental neutron activation analysis (INAA) and compiled data as information values. The
compiled data for chlorine and bromine were reported by
Reference8 and in the certificates of analysis for individual
USGS materials. Literature values for iodine were obtained by
ICPMS. In the cases where IC or ICPMS were used, pyrohydrolysis concentration for halogen or the other chemical treatment was performed. Additionally, halogen concentration
measurements by the noble gas method are reported,18 andthese results are also included in Table 3. A comparison of ourdata with the literature data is discussed in the following sections.

3.2. Comparison of RNAA data with literature data for
USGS reference materials other than basalt, andesite andmanganese nodule materials. Eleven USGS materials otherthan basalts (BHVO-2, BCR-2, BIR-1a), andesite (AGV-2), andmanganese nodules (Nod-P-1 and Nod-A-1) are presented inthis section. Five USGS materials out of 11 have no literature
values for halogens: DTS-2b (dunite), COQ-1 (carbonatite),
CLB-1 (coal), SBC-1 (marine shale) and DGPM-1 (disseminated gold ore). Two USGS materials out of 11 have only
information values for chlorine, W-2a (diabase) and SGR-1b(shale rock), where RNAA values are consistent with the information values within uncertainties of 30%. Three USGS
materials, DNC-1a (dolerite), QLO-1a (quartz latite) andSDC-1 (mica schist), have some kind of literature values, and
RNAA values are approximately consistent with those literature values, except for chlorine in DNC-1a and the compiled
bromine values in QLO-1a. Since DNC-1a is a second bottlingof the original DNC-1 material, the chemical composition of
DNC-1 can be used in the comparisons with DNC-1a. For
chlorine in DNC-1a (DNC-1), the literature values are two to
three times higher than the RNAA value, which is a meanvalue of replicate analysis results. In our RNAA results, thechlorine value for DNC-1a has relatively larger uncertainty
than those for BIR-1a and DTS-2b which have chlorine con-J. Nucl. Radiochem. Sci., Vol. 20, 2020

Accurate determination of three halogen elements (Cl, Br, and I) in U.S.

tents lower than that of DNC-1a. In general, a larger uncertainty is to be obtained from a measured value with poorer
counting statistics, corresponding to a lower elemental content. In this case, however, variation of the four measured values in DNC-1a (shown in Appendix) causes the larger
uncertainty in the chlorine value for DNC-1a, suggesting heterogeneity of the halogen distribution in DNC-1a (and/or DNC1). The heterogeneity of halogen in the USGS materials
analyzed in our previous study4 is discussed in detail in thelast section before the conclusion. Such heterogeneity may be
responsible for inconsistency in the chlorine values between
RNAA and the literature data, although the quality of XRF
data in DNC-19 is doubtful. For DNC-1a and SDC-1, the bromine values obtained by RNAA are consistent with their upper
limit values obtained by INAA,10 and for QLO-1a, the bromine
value obtained by RNAA is in good agreement with that by
INAA.10 This may suggest that the data quality of two values
from RNAA and INAA for QLO-1a is better than that of thetwo information values, and it is entirely reasonable that
RNAA data have higher sensitivity and accuracy than INAA
data. For the final material, GSP-2, data obtained by RNAA
and noble gas method agree within uncertainties for both chlorine and bromine, whereas for iodine the value of the noble gas
method is lower than the RNAA value. This inconsistency foriodine between the noble gas method and RNAA is also foundin the basalt and andesite samples as shown in the next section.
To elucidate the tendency of the noble gas method giving lower
values than the RNAA method, further studies along this line
are in progress. Regarding GSP-2, the RNAA value is consistent with the literature value of chlorine obtained by various
methods11 within uncertainties. Since we have demonstrated
that the RNAA procedure applied in our previous study4 iseffective in determining halogens in geological rock samples,
we envisage that our RNAA data will be ref lected in any
future compilation in the establishment of a database of USGS
geochemical reference materials.
3.3. Comparison of RNAA data with literature data for
BHVO-2, BCR-2, BIR-1a and AGV-2. The three basalts(BHVO-2, BCR-2 and BIR-1a) and the andesite (AGV-2) analyzed using RNAA in our previous study4 were also analyzed
using IC12-14,17 for chlorine, ICPMS12, 13 for bromine and iodine,and the noble gas method18 for the three halogens. First, our
RNAA data are compared with the IC and ICPMS data. As
the pretreatment of IC and ICPMS, the three halogens werepreconcentrated using pyrohydrolysis, in which the rock materials are heated with vanadium pentoxide under an oxygen
flow in an electric furnace and the expelled halogens are thentrapped into an alkaline solution. Each experimental condition of the pyrohydrolysis is described in the literature.12-14, 17
In terrestrial rock materials, halogens are expected to be present in the form of a monovalent anion, such as F-, Cl-, Br-, and
I-. In pyrohydrolysis, some halogens (at least, chlorine, bromine and iodine) are expected to be mostly oxidized to gaseous halogen molecules (dimer) like Cl2, Br2 and I2,19, 20 which
are trapped in alkaline solution, where they are probably in theform of a monovalent anion. The solution is then introduced
into the IC and ICPMS instruments. In the analytical procedure of Reference12, the solutions obtained from pyrohydrolysis are slowly evaporated in order to concentrate the solution
by a factor of around ten. Reference13 used the same analyticalprocedure as Reference12.
As already mentioned, the USGS materials were each analyzed two to four times in our previous study4 and the values
obtained4 were reasonably consistent with one another for eachhalogen. Our RNAA data for BHVO-2, BCR-2, BIR-1a andAGV-2 are mostly consistent with the literature data for chlorine and bromine, but not for iodine. As for bromine in
BHVO-2, BCR-2 and AGV-2, where two ICPMS values were16

TABLE 4: Ratio of IC Value to RNAA ValueasampleIC/ RNAA a

BHVO-2(Michel and Villemant)
BHVO-2(Balcone-Boissard et al)
BHVO-2(Wang et al)
BHVO-2(Shimizu et al)
BCR-2(Michel and Villemant)
BCR-2(Wang et al)
BCR-2(Shimizu et al)
BIR-1a / BIR-1(Shimizu et al)
AGV-2(Michel and Villemant)
AGV-2(Wang et al)

1.44 ± 0.21
0.78 ± 0.11
0.85 ± 0.08
0.81 ± 0.06
0.88 ± 0.07
0.80 ± 0.06
0.84 ± 0.04
1.01 ± 0.09
1.03 ± 0.06
0.84 ± 0.05

Arithmetic mean

0.87 ± 0.09 b

RNAA and IC values from Table 3.
A ratio for BHVO-2 (Michel and Villemant) is ruled out (seetext for details). An uncertainty means a standard deviation
(1σ).

b

reported by Reference12. The RNAA values are consistent
with one of those two values within uncertainties of 10%. For
bromine in BIR-1a, using the chemical composition of BIR-1
for the comparison in the same way that DNC-1 was used torepresent DNC-1a, our RNAA value is also in agreement with
the ICPMS value reported by Reference12 within uncertainties.
The bromine content of this material is lowest among the 17
USGS materials analyzed in our previous study4. As foriodine in BHVO-2, BCR-2, BIR-1a and AGV-2, however, the
RNAA values are not consistent with ICPMS values reported
by Reference12 and Reference13. The RNAA values vary from
0.041 mg kg -1 for BIR-1a to 0.307 mg kg -1 for BHVO-2,
whereas the ICPMS values are much lower. The ICPMS values were also very similar, spanning a much smaller range,
especially in BHVO-2, BCR-2 and BIR-1, where they varied
from 0.014 mg kg-1 to 0.020 mg kg-1. Such an inconsistency
between RNAA values and ICPMS values may be due to a lossof iodine during the preconcentration in the analytical procedure.
Presumably the loss of iodine could have occurred in theprocedure used by Reference12 and by Reference13, where thesolutions obtained from pyrohydrolysis were slowly evaporated in order to concentrate the solution by a factor of aroundten. Bulk iodine could be lost in the solutions during the concentration by evaporation, such that the amount of residual
iodine in the concentrated solutions could be very similar.
This suggests that the concentration of the solution after pyrohydrolysis by evaporation should not be used for the determination of iodine.
To discuss the chlorine content, our RNAA values werecompared to the IC values of References12-14, 17 for BHVO-2,
BCR-2, BIR-1a and AGV-2 in Table 4. The ratios of IC values
to RNAA values given in the table are plotted in Figure 1. In
calculating the mean ratio, a value for BHVO-2 reported by
Reference12 was ruled out using the outlier test under the
2σ-criterion. An uncertainty quoted for each ratio is simply
the value calculated from two individual uncertainty values
accompanied by RNAA and IC data. Although the IC values
are very consistent with the RNAA values for BIR-1a (BIR-1)
and AGV-2 reported by Reference17 and Reference12, respectively, it can be seen that the IC data show systematically lower
values than the RNAA data by a factor of 0.87±0.09. It is presumed that the quantitative collection of chlorine cannot
always have been achieved in the pyrohydrolysis procedureused by References12-14, 17. A similar situation for bromine andiodine in sedimentary rock reference samples has been pointed

J. Nucl. Radiochem. Sci., Vol. 20, 2020

Sekimoto

Ratio=1
Mean(0.87s0.09)

1
1 region

AGV-2

Wang et al.

Shimizu et al.

Wang et al.

Michel and Villemant

Shimizu et al.

BIR-1a/BIR-1

BCR-2

Shimizu et al.

Michel and Villemant

Wang et al.

BHVO-20.5

Balcone-Boissard et al.

Ratio of IC to RNAA

1.5

Michel and Villemant

17

Figure 1. Chlorine concentration ratio, IC value over RNAA value.

out in our previous work.3 This suggests a limitation of thepyrohydrolysis procedure in the determination of halogens(especially chlorine) by IC. It may be noted, however, that
RNAA and IC data agree within 15% for chlorine, as shownby the mean value of individual ratios, and further that IC coupled with pyrohydrolysis can work well for such studies where
only rough abundances of halogens are required and for materials with chlorine content varying from 5 mg kg-1 (BIR-1a) toaround 100 mg kg-1 (such as in BHVO-2 and BCR-2). An
advantage of choosing RNAA for halogen analysis is noted
elsewhere.3
Comparing the values of the noble gas method with the
RNAA values in BHVO-2 and BCR-2, the former values are
consistent with the latter ones within uncertainties of 3σ forchlorine and bromine in BHVO-2 and for bromine and iodine
in BCR-2. As for chlorine in BCR-2 both of the two values
agree within 10%, although that of the noble gas method islower than that of the RNAA considering uncertainties of 3σ.
Regarding iodine in BHVO-2, the noble gas method value isapparently lower than that of the RNAA. Since uncertainties
are not evaluated in values of the noble gas method for BIR-1aand AGV-2, the RNAA values for these two materials cannot
be compared with values of the noble gas method in detail.
For the four materials of interest in this section and GSP-2, foriodine, the values of the noble gas method tend to be lower
than the RNAA values. As already mentioned in the previous
section, this inconsistency is under investigation. Considering
the data quality of our RNAA values as discussed above andelsewhere,3 our RNAA data for the four USGS materials considered in this section would contribute to any future compilation in the establishment of a database of USGS geochemicalreference materials.
3.4. Comparison of RNAA data with literature data for
manganese nodule materials. The two manganese nodules(Nod-P-1 and Nod-A-1) analyzed using RNAA in our previous
study4 were also analyzed using inductively coupled plasma
double focusing sector field mass spectrometry (ICPSFMS)16
for bromine and iodine. Before analysis by ICPSFMS, thenodule materials were subjected to an acid digestion proce-dure, in which the nodule materials are heated with a mixtureof concentrated nitric, hydrochloric and hydrofluoric acids byusing microwave. The digestion solution was diluted appropriately and then introduced into the ICPSFMS instrument.
Our RNAA data for Nod-P-1 and Nod-A-1 are not consistent with the literature data obtained by ICPSFMS for either
bromine or iodine. In the case of iodine the ICPSFMS values
are lower than the RNAA values. Such an inconsistency
between RNAA values and ICPSFMS values also may bederived from the loss of iodine in the acid digestion procedure
involving heating by microwave. 21 To prevent the loss of
iodine, nitric acid should not be used for an acid digestion inprinciple, and heating of the digestion solution must be
achieved with extreme care. Regarding bromine, on the other
hand, the ICPSFMS values are higher than the RNAA values
by a factor of about three to five. Such an inconsistency
between RNAA values and ICPSFMS values may be due tothe interference effect of this ICPSFMS instrument.22 Bromine
is determined by ICPSFMS and/or ICPMS using the isotopes
79
Br and 81Br. The mass of those two bromine isotopes is very
close to the biatomic (40Ar40Ar)+ molecule of mass 80. Since
argon is so abundant in the plasma of the ICPSFMS and/or
ICPMS, the combination of two 40Ar ions causes a large peakat mass 80 whose peak tail could interfere with either stable
isotope of bromine. Additionally, there are several potential
interferences on 79Br and 81Br: (40Ar39K) +, (63Cu16 O) + and(40Ar38Ar1H)+ interference with 79Br; and (40Ar41K)+, (65Cu16O)+
interference with 81Br signals.22 To quantify 79Br successfully
w it hout i nt e r fe r e nc e f rom ( 4 0 A r 39 K) + , ( 63 C u 16 O) + , or
(40Ar38Ar1H)+, the ICPSFMS instrument should be operated inresolution (m/δm) of >10,200, >12,800, or >5,400, respectively.
(The required resolution for successful quantification of 79Br is
explained in Appendix.) In case of the literature values for bromine, however, the ICPSFMS instrument was operated in
medium resolution mode (m/δm=4,500) for 79Br, so interference from (40Ar39 K) + and (63Cu16 O) + could not have been
removed from the 79Br signal. Thus a possible explanation forhigher bromine values in ICPSFMS than in RNAA could bean overestimation due to the interference at mass 79 in the
ICPSFMS instrument. Since ICPSFMS operation in high res-J. Nucl. Radiochem. Sci., Vol. 20, 2020

Accurate determination of three halogen elements (Cl, Br, and I) in U.S.

18

TABLE 5: RSD values with each halogen mean value for USGS materials
ChlorineaBromineIodineSample code

RSD
(1σ: %)

Contents(mg kg-1)

RSD(%)

Contents(mg kg-1)

RSD(%)

Contents(mg kg-1)

BCR-2
BIR-1a
Nod-P-1
DTS-2b
CLB-1
SBC-1
W-2a
DNC-1aQLO-1a
GSP-2

1.1
7.6
10.4
2.4
12.8
9.6
10.2
17.9
6.7
8.1

112 ± 15.64 ± 0.431380 ± 144
10.7 ± 0.3
1190 ± 152
24.9 ± 2.4
220 ± 2218.1 ± 3.2
244 ± 16363 ± 29

-a
32.4
12.9
2.1
13.0
1.3
13.0
20.2
5.0
17.0

0.144 ± 0.008
0.039 ± 0.012
5.93 ± 0.76
0.093 ± 0.002
52.1 ± 6.8
0.355 ± 0.005
0.309 ± 0.040
0.063 ± 0.013
1.03 ± 0.05
0.117 ± 0.020

27.0
20.7
11.1
18.8
8.6
3.8
17.6
18.1
11.9
23.3

0.082 ± 0.022
0.041 ± 0.009
157 ± 170.789 ± 0.148599 ± 52
5.07 ± 0.19
0.405 ± 0.071
0.102 ± 0.018
0.741 ± 0.088
0.075 ± 0.018

Not given (see text for details).

olution mode (HRM) is generally at a resolution (m/δm) of
10,000, it is fundamentally difficult to quantify 79Br successfully without interference of (40Ar39K) + and (63Cu16O) + evenusing the HRM. This suggests that bromine separation as apretreatment of samples is essential for bromine determination
using ICPSFMS and/or ICPMS.

als with higher halogen contents as described above. However,
Nod-P-1 and CLB-1 have relatively high RSD values in bromine, although their bromine contents are high. A similar situation can be seen for chlorine.

(a) Chlorine30

RSD (%)

USGS
GSJ

20

DNC-1aCLB-1

10
Nod-P-1

0 -2
10

10-1

100

101

102

103

Cl contents (ppm)(b) Bromine

30

RSD (%)

USGS
GSJ

20

DNC-1a

Nod-P-1

CLB-1

10

0 -2
10

10-1

100

101

102

103

Br contents (ppm)(c) Iodine

30

USGS
GSJ

DNC-1aRSD (%)

3.5. Heterogeneity of halogen in USGS materials.
Although reference materials are expected to be homogeneousin elemental content, some materials, such as sedimentarymaterials, have been reported to be inhomogeneous due to heterogeneities in their constituent minerals.23 Here we discussheterogeneities of halogens in the ten USGS materials forwhich we have determined three or four analytical values
using RNAA.4 The discussion of homogeneity or heterogeneity of a material generally involves sample mass, that is, amaterial may be homogeneous for an element in 1 g of sample
but may be inhomogeneous in 100 mg of sample. Since about
20-300 mg of USGS materials were treated in RNAA,4 homogeneity or heterogeneity for the ten USGS materials can be
discussed in restricted sample mass. It is meaningful to makesuch discussion even in restricted sample mass, because a few
tens or hundreds mg of those reference materials are usuallyused for chemical analysis using ICPMS, NAA, etc.
As already mentioned, each uncertainty value for those ten
USGS materials is one sigma of standard deviation in the individual (three or four) analytical values for the corresponding
materials. The relative standard deviation (RSD) values areshown in Table 5. The RSD for bromine in BCR-2 is not given
because the bromine value in BCR-2 is the mean of just two
analytical values. These RSD values are controlled by thevariance among three or four analytical values. The varianced e p e n d s o n i n c i d e n t a l u n c e r t a i n t y i n o u r R NA A .
Consequently, the RSD values obtained in our RNAA are
affected by incidental uncertainty. The incidental uncertainty
may occur in gamma-ray counting and in weighing out powder samples and chemical standard solutions for quantification, and heterogeneity in powder samples maybe also a factorof the incidental uncertainty. In USGS materials containing
higher halogen contents, generally, the RSD values tend to
become lower. The RSD values shown in Table 5 are plottedagainst the chlorine, bromine, and iodine contents in Figure2(a-c), respectively. The RSD values against the halogen contents in 12 reference materials prepared by Geological Surveyof Japan (GSJ) are also shown in this figure. Their values andcontents are obtained by RNAA in our previous study3 andtabulated in Appendix. For bromine and iodine, it can be seenthat the RSD values tend to be lower in USGS and GSJ materi-20
Nod-P-1

10
CLB-1

0 -2
10

10-1

100

101

102

103

I contents (ppm)

Figure 2. RSD values versus Cl, Br and I contents for the USGS and
GSJ materials. (a) Cl, (b) Br, and (c) I.

19

J. Nucl. Radiochem. Sci., Vol. 20, 2020

Considering that both the 10 USGS and the 12 GSJ materials are analyzed by RNAA in the same way, the incidental
uncertainty which raises those two RSD values may be likely
to derive from heterogeneity in powder samples rather than an
accident in experimental procedure. At the present stage,
however, we are not able to conclude that CLB-1 and Nod-P-1
can be inhomogeneous in halogens, because sample mass of
CLB-1 and Nod-P-1 used in RNAA was sometimes smaller(20-50 mg) than the masses of the other materials analyzed.
(Sample mass used in each analytical r un is shown inAppendix.) Heterogeneity of halogen distribution in DNC-1a
was also suggested above in Results and Discussion, section 2.
To investigate the heterogeneity of halogens in those twomaterials as well as the other materials in detail, several aliquots of materials with different weights should be studied by
RNAA.
4. Conclusions
Through an exhaustive comparison of our halogen data
determined by RNAA with the corresponding data in literature, the following findings have been made in relation to theindividual reference materials.
For DTS-2b (dunite), COQ-1 (carbonatite), CLB-1 (coal),
SBC-1 (marine shale) and DGPM-1 (disseminated gold ore),
there are no literature values for halogens. Chlorine, bromine,
and iodine values for those five reference materials are firstreported by using RNAA.
For W-2a (diabase) and SGR-1b (shale rock), our RNAA values for chlorine are consistent with the literature (information)
values within uncertainties of 30%. Bromine and iodine values for those two reference materials are first reported byusing RNAA.
For DNC-1a (dolerite), QLO-1a (quartz latite) and SDC-1(mica schist), our RNAA values for chlorine and bromine areapproximately consistent with the literature values, except forchlorine in DNC-1a. The iodine values for these three reference materials are first reported by using RNAA.
For GSP-2 (granodiorite), our RNAA values for chlorine
and bromine are consistent with the literature values, whereas
the literature value for iodine is lower than the RNAA value.
For BHVO-2, BCR-2, BIR-1a (basalts), and AGV-2 (andesite), our RNAA values for bromine are consistent with the corresponding literature values, whereas the literature values foriodine are lower than the RNAA values. Such an inconsistency between RNAA values and literature values obtained by
ICPMS can be explained by a loss of iodine in pretreatment for
ICPMS, where the solutions obtained from pyrohydrolysis
were slowly evaporated in order to concentrate the solution.
The literature values for chlorine are systematically lower thanthe RNAA values by a factor of 0.87±0.09, suggesting thatchlorine cannot be quantitatively extracted from basalt andandesite materials.
For Nod-P-1 and Nod-A-1 (manganese nodules), the literature values for iodine are lower than the corresponding RNAA
values. Such an inconsistency between RNAA values and literature values can also be explained by the loss of iodine in
pretreatment for ICPSFMS, where powder samples are subjected to an acid digestion procedure with using nitric acid andheating by microwave. The bromine values obtained by
ICPSFMS (literature values) are higher than the RNAA values
by a factor of about three to five. A possible explanation foran overestimation by ICPSFMS could be an interference atmass 79 which is used for bromine determination.
Finally, the heterogeneity of halogens in USGS materials
was assessed by using their RSD values and contents. To

Sekimoto
investigate the heterogeneity of halogens in CLB-1 and NodP-1 in detail, several aliquots of materials with different
weights should be studied by RNAA.
Acknowledgments
The authors express their gratitude to the members of theresearch reactor group in Institute of Integrated Radiation and
Nuclear Science, Kyoto University (KURNS) for the preparation and operation in the neutron irradiation and to a program
for the cooperative use of KUR supported by Kyoto University.
We thank Dr. S. Fukutani (KURNS) and Prof. T. Fujii (Osaka
University) for their helpful suggestion and comments in discussion about bromine in manganese nodules and heterogeneity in USGS materials. We are grateful to Dr. J. Bennett(Australian national nuclear research and development organization, ANSTO) for his English correction and valuable comments. The USGS materials were supplied through joint
research project between Shimizu Corporation and KURRI.
This study was partly supported by the Mitsubishi foundation(2015), the Sumitomo foundation (2015), the Iwatani foundation (2015), JSPS KAKENHI Grant numbers JP18H01312,
JP19K21993 (to SS).
References(1) B. Deruelle, G. Dreibus, and A. Jambon, Earth Planet. Sci.
Lett. 108, 217(1992).
(2) C. K. Unni and J. G. Schilling, Nature. 272, 19(1978).
(3) S. Sekimoto and M. Ebihara, Anal. Chem. 85, 6336 (2013).
(4) S. Sekimoto and M. Ebihara, Geostand. Geoanal. Res. 41,
213(2017).
(5) M. Ebihara, N. Saito, and H. Akaiwa, J. Radioanal. Nucl.
Chem. 108, 241(1986).
(6) M. Ebihara, N. Saito, H. Akaiwa, and K. Tomura,Radioisotopes. 40, 433(1991).
(7) H. Ozaki and M. Ebihara, Anal. Chim. Acta. 583,
384(2007).
(8) K. Govindaraju, Geostand. Newslett. 18, 1(1994).
(9) J. G. Arnarson and D. K. Bird, Econ. Geol. 95, 945(2000).
(10) R. L. Korotev, Geostand. Newslett. 20, 217(1996).
(11)Z. E. Peterman and P. L. Cloke, Appl. Geochem. 17,683(2002).
(12) A. Michel and B. Villemant, Geostand. Newslett. 27,
163(2003).
(13) H. Balcone-Boissard, A. Michel, and B. Villemant,
Geostand. Geoanal. Res. 33, 477(2009).
(14) Q. Wang, A. Makishima, and E. Nakamura, Geostand.
Geoanal. Res. 34, 175(2010).
(15) D. Hanano, D. Weis, J. S. Scoates, S. Aciego, and D. J. De
Paolo, Geochem. Geophys. Geosyst. 11, Q01004(2010).
(16) M. D. Axelsson, I. Rodushkin, J. Ingri, and B. Öhlander,
Analyst. 127, 76(2002).
(17) K. Shimizu, K. Suzuki, M. Saitoh, U. konno, S.
Kawagucci, and Y. Ueno, Geochem. J. 49, 113(2015).
(18) M. A. Kendrick, J. D’andres, P. Holden and T. Ireland,
Geostand. Geoanal. Res. 42, 499(2018).
(19) B. Schnetger and Y. Muramatsu, Analyst. 121, 1627(1996).
(20) J. Y. Chai and Y. Muramatsu, Geostand. Geoanal. Res. 31,
143(2007).
(21) L. H. Pacquette, A. M. Levenson, and J. J. Thompson, J.
AOAC. Int. 95, 169(2012).
(22) J. Hammerli, B. Rusk, C. Spandler, P. Emsbo, and N. H. S.
Oliver, Chem. Geol. 337–338, 75(2013).
(23) C. Chauvel, S. Bureau, and C. Poggi, Geostand. Geoanal.
Res. 35, 125(2011).