A Simple and Fast Separation Method of Fe Employing Extraction Resin for Isotope Ratio Determination by Multicollector ICP-MS

doi:10.4236/ijamsc.2013.12012

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International Journal of Analytical Mass Spectrometry and Chromatography, 2013, 1, 95-102

Published Online December 2013 (http://www.scirp.org/journal/ijamsc)

http://dx.doi.org/10.4236/ijamsc.2013.12012

Open Access IJAMSC

A Simple and Fast Separation Method of Fe Employing

Extraction Resin for Isotope Ra tio Determi nation by

Multicollector ICP-MS

Akio Makishima

The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry (PML), Institute for Study of the Earth’s Interior,

Okayama University, Misasa, Tottori, Japan

Email: max@misasa.okayama-u.ac.jp

Received October 17, 2013; revised November 13, 2013; accepted December 16, 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

A new, simple and fast separation method for Fe using an extraction chromatographic resin, Aliquat 336 (commercially

available as TEVA resin) has been developed. A one milliliter column containing 0.33 mL TEVA resin on 0.67 mL

CG-71C was used. Iron was adsorbed with 6 mol·L−1 HCl + H2O2 on TEVA resin, and recovered with 2 mol·L−1 HNO3.

The recovery yield and total blank were 93.5 ± 6.5% and 6 ng, respectively. The separation method is simple, and takes

<2 hours. For evaluation of the Fe separation, Fe isotope ratios were measured by a double-spike method employing

multicollector inductively coupled plasma source mass spectrometry (MC-ICP-MS) with repeatability of 0.06‰ (SD)

for the standard solution and ~0.05‰ for the silicate samples. Therefore, the column chemistry developed in this study

is a viable option for Fe isotope ratio measurement by MC-ICP-MS.

Keywords: Fe Separation; Fe Isotope Ratio; Multicollector Inductively Coupled Plasma Source Mass Spectrometry

1. Introduction

Trioctylmethylammonium chloride (Aliquat 336) works

as an anion exchanger, and is used in extraction chroma-

tography (commercially sold as TEVA resin) [1]. Yang

and Pin [2] and Grahek and Macefat [3] have tried to use

the TEVA resin for Fe separation. The eluent volumes of

60 mL for 1 mL of the TEVA resin and 120 mL for 3 g

(equates ~2.7 mL) TEVA resin were used, respectively.

However, these volumes are too mamy to handle; large

space is required and evaporation takes a long time. Re-

cently, Makishima and Nakamura [4] successfully puri-

fied Zn using a one milliliter column composed of 0.33

mL TEVA resin on 0.67 mL CG-71C resin. They used

the advantage of acid resistance of the TEVA resin [5],

namely, HNO3 was used in the final step to recover Zn

that was strongly adsorbed on the resin. Based on this

novel finding, it was noticed that the anionic character of

the TEVA resin could be applied to separation of Fe.

This study applies the TEVA resin for purification of Fe

for isotope ratio measurements using multicollector

(MC)-ICP-MS for the first time.

An advantage of the new TEVA resin column chemis-

try is that the whole column chemistry (from sample

loading to Fe collection) finishes <2 hours. Anion ex-

change resins, AG 1X8 or AG MP-1 employing Fe(III)

chloro complex are commonly used [6,7]. In a one milli-

liter of AG 1X8 column case, for example, the total

volume of 55 mL [7], was used from washing the column

to collection of Fe. Using an AG MP-1 column, total

elution volume for Fe was reduced to 22 mL [6].

For evaluation of column chemistry and mass spec-

trometry developed in this study, three USGS (the US

Geological Survey) standard silicate reference materials,

seven GSJ (the Geological Survey of Japan) standard

silicate reference materials and three carbonaceous chon-

drites of Orgueil, Murchison and Allende were used as

test samples. Then Fe isotope ratios were measured using

a double spike method [8-11] at high mass resolution by

MC-ICP-MS to show the validity of the method.

2. Experimental

2.1. Reagents

All experiments were performed in clean rooms and

clean benches with HEPA (High Efficiency Particulate

A. MAKISHIMA

Air) filter in the Pheasant Memorial Laboratory (PML)

[12]. Water and HF were purified as described elsewhere

[12]. Hydrochloric acid was distilled by a Teflon-two-

bottle distiller [12]. TAMAPURE-AA-100 grade per-

chloric acid (Tama Chemicals Co., Ltd., Japan), electric

industry (EL) grade HNO3 and ultrapure hydrogen per-

oxide (Kanto Chemical Co. Inc., Japan) were used with-

out purification. Six mol·L−1HCl with 0.05 % (v/v) H2O2

was prepared just before the column chemistry. For the

column calibration, two multi-element standard solutions

(Specpure, Nos. 42885 and 44270, Alfa Aesar, USA)

were used.

CAUTION: HF, HCl, HNO3, HClO4 and H2O2 are

highly corrosive and toxic. Inhalation and contact with

skin and eyes should be avoided. They should be handled

with protective glasses and gloves.

Iron standard metal, IRMM-014 was dissolved, and

finally diluted into 1 μg·mL−1 with 0.5 mol·L−1 HNO3

and used as the isotopic standard for MC-ICP-MS. TE-

VA extraction resin (100 - 150 μm, Eichrom Technolo-

gies, Inc., USA) and Amberchrom CG-71C (Rohm and

Haas, Co., USA) were soaked and stored in water. TEVA

resin and CG-71C were not reused.

2.2. Iron Double Spike

A 57Fe-58Fe double spike [10,11] was chosen. Iron iso-

topes of 57Fe and 58Fe, with enrichments of 86.06 and

73.51%, respectively, were purchased from Oak Ridge

National Laboratory (USA). Each spike was dissolved

and diluted with HNO3, then mixed and used as a Fe

double spike. Ideal isotopic abundances of the double

spike were 47.65 and 52.35% for 57Fe and 58Fe, respec-

tively [10], and the best sample: spike mole ratio is 55:45

[10]. Therefore, 1 μg sample Fe was mixed with 0.8 μg

double-spike. To keep this ratio, the Fe concentration in

the sample solution was determined before the spike ad-

dition by high-resolution ICP-MS [13].

2.3. Silicate Samples

Three USGS silicate reference materials, BHVO-1 (ba-

salt), AGV-1 (andesite) and PCC-1 (peridotite) and seven

GSJ silicate reference materials, JB-1, JB-2, JB-3 (ba-

salts), JA-1, JA-2, JA-3 (andesites) and JP-1 (peridotite)

were used as test samples. Powder of bulk carbonaceous

chondrites, Orgueil (CI1), Murchison (CM2) and Allende

(CV3) were also employed.

2.4. TEVA Resin Column and Silicate Sample

Solution

The TEVA resin column was prepared by packing 0.33

mL of TEVA resin on 0.67 mL of CG-71C in a 1 mL

polypropylene column (5 cm × 5 mm in diameter, Muro-

machi Chemicals Inc., Japan) [4]. The CG-71C resin was

used for absorbing organic materials and controlling the

elution rate.

Silicate powder samples were digested by a usual

sample digestion method in our laboratory [13]. In short,

samples were digested with HF-HClO4, dried to decom-

pose fluorides with HClO4 again [14], evaporated with

HCl, and finally dissolved with 0.5 mol·L−1 HNO3. The

final dilution was typically ~250 times (20 mg silicate

samples into 5 mL).

2.5. Iron Separation by the TEVA Resin Column

A Fe separation procedure using the TEVA resin column

is summarized in Table 1. All H2O2 concentration in

Table 1 is 0.05 % (v/v) H2O2. The resin bed was washed

twice with 2 mol·L−1 HNO3, subsequently washed once

with 6 mol·L−1HCl, and conditioned. The sample solu-

tion containing 1 μg of Fe was added with the solution

containing 0.8 μg Fe double spike and 0.6 mL of 6

mol· L −1 HCl, and dried. Then the sample was dissolved

with 0.1 mL of 6 mol·L−1 HCl with H2O2, loaded on the

resin bed and left for 5 min (see Results and Discussion).

The major elements were washed away by addition of

3.2 mL of 6 mol·L−1 HCl with H2O2. Then Fe was col-

lected with 6.4 mL of 2 mol·L−1 HNO3. The Fe fraction

was dried at 80˚C for 10 hours with one drop of HClO4

to decompose organic materials and small resin particles.

To evaporate HClO4 completely, the sample was finally

heated at 195˚C for 6 hours. Then the purified Fe was

dissolved with 1 mL of 0.5 mol·L−1 HNO3, which is

ready for MC-ICP-MS measurement.

Although the flow rate of the TEVA column is 0.3

mL· mi n −1, which is rather high, breakthrough of Fe does

not occur. As the total elution volume including washing

of the column is 32.1 mL, the column chemistry can be

finished within two hours including washing and condi-

tioning the resin bed. This is one of the largest advan-

tages of the TEVA resin column chemistry developed in

this study. In a case of 1 mL of AG 1X8, the flow rate of

a column is ~0.2 mL·min−1, and the total elution volume

is ~55 mL [7]. Thus it takes more than 5 hours to collect

Fe. In addition in other studies, one pass of anion ex-

Table 1. Chemical procedure for Fe purification using TE-

VA resin column.

2 mol·L−1 HNO3 6.4 mL

water 1.6 mL

2 mol·L−1 HNO3 6.4 mL

water 1.6 mL

Washing

6 mol·L−1 HCl 3.2 mL

Conditioning 6 mol·L−1 HCl + H2O23.2 mL

Loading the sample (leave 5 min) 6 mol·L−1 HCl + H2O20.1 mL

Removing major elements 6 mol·L−1 HCl + H2O23.2 mL

Collecting Fe 2 mol·L−1 HNO3 6.4 mL

Open Access IJAMSC

A. MAKISHIMA 97

change column is not enough, and the column chemistry

is repeated twice or three times to purify Fe in some

cases [7].

The combination with the double spike technique of

this column chemistry gives another advantage that the

Fe isotope determination is more tolerable to loss of iron,

which could occur in the column chemistry.

2.6. Measurement of Fe Isotope Ratios

Isotope ratios of Fe were measured by an MC-ICP-MS,

NEPTUNE housed in PML. Details of the MC-ICP-MS

operating conditions are shown in Table 2 . The spiked 1

μg·mL−1 of Fe solution generally gave ~2 × 10−10 A sig-

nal for 56Fe+, 57Fe+ and 58Fe+. One run consists of 70

scans, but the first 40 scans were not used and the fol-

lowing 30 scans were used, because the signal increased

slowly and stabilized after around 40 scans. Thirty sets of

isotope ratios of 56Fe/54Fe, 57Fe/54Fe and 58Fe/54Fe

Table 2. MC-ICP-MS operating conditions.

1) Sample introduction and ICP conditions

Nebulizer Micro-flow PFA nebulizer,

PFA-50 (ESI, USA)

self-aspiration

flow rate: ~50 μL·min−1

Plasma power 1.2 kW (27.12 MHz)

Torch Quartz glass torch

with a sapphire injector

Plasma Ar gas flow rate 15 L·min−1

Auxiliary Ar gas flow rate 0.80 L·min−1

Nebulizer Ar gas flow rate 0.90 L·min−1

2) Desolvator conditions

Desolvator ARIDUS II

Spray chamber temperature 110˚C

Desolvator temperature 160˚C

Sweep gas (Ar) 8 - 9 L·min−1

3) Interface

Sampling cone Made of Ni

Skimmer cone Made of Ni (X-skimmer)

4) Data acquisition conditions

Resolution M/ΔM= ~7000

Washingtime 480 sec after measurement

Uptake time 90 sec

Background data integration 4 sec for 1 scan, 20 scans in one run

On-top zeroes

Sample data integration 4 sec for 1 scan, 30 scans in one run

5) Cup configuration

L4 L2 L1 C H1 H2 H4

52Cr* 53Cr* 54Fe 56Fe 57Fe 58Fe 60Ni

*An amplifier with a 1 TΩ resistor.

were obtained for each sample, and the averages of each

ratio were calculated. Then the double spike calculation

(see the next section) was performed. One T ohm resistor

amplifier [15] was used (see Table 2), and 52Cr and 53Cr

were sometimes observed. Isobaric interference of 54Cr

was corrected using 54Cr/52Cr = 0.11339, a power law,

and a normalizing value of 53Cr/52Cr = 0.028226 [16].

Nickel interference was corrected using 58Ni/60Ni = 2.62.

The Fe isotope fractionation is expressed as a per mil

difference from that of the Fe standard, IRMM-014 [17]

by the following equation:





5656 5456 54

sampleIRMM 014

FeFe FeFe Fe1

1000























(1)

2.7. Double Spike Calculation

A theory of a double spike is briefly explained in this

section. Each Fe ratio is written using an exponential law

as follows:





norm- 54smp545454

56,57 and 58

iii

mm m









(2-4)

where mi is a mass of iFe; Rnorm-i/54 and Rsmp-i/54 indicate

normalizing and sample isotope ratios of iFe/54Fe. In this

study, Rnorm-i/54 (i = 56, 57 and 58) are 15.698, 0.36233

and 0.048080, respectively, which are those of the stan-

dard IRMM-014 [17]. It should be noted that Rnorm-i/54

and mi are constants.



is a mass fractionation factor,

which is a product of mass fractionation of the sample

and mass discrimination during analysis.

When there is no fractionation in the sample,



equal to 0. Thus the sample isotope ratios become equal

to those of IRMM-014. The purpose is to determine

Rsmp-i/54. For this purpose, a double spike method has

been developed [8-11].

The spike isotope ratios of Rspike-i/54 (i = 56, 57 and 58)

also follow the similar equations:





spike 54pike545454

56,57 and 58

isi i

mm m





 







(5-7)

When the spike isotope ratios are measured, only

Rspike’-i/54 are obtained, and Rspike-i/54, which are isotope

ratios without mass fractionation (



' = 0), cannot be de-

termined. The method for determination of Rspike-i/54,

which is called as “spike calibration”, is described later.

For the spike-sample mixture, the following equations

hold:







mixsmp spik5454 54e

56,

R RR

57 and 58

iii











(8-10)



 



mix 54mix545454

56, 57and58

iii

RRmm m





 



 (11-13)

Open Access IJAMSC

A. MAKISHIMA

where b is mixing mole ratio of the sample to the spike.

The three isotope ratios of the spike-sample mixtures

(Rmix'-i/54; i = 56, 57 and 58) are measured. As there are

nine variables (Rsmp-i/54, Rmix-i/54, b,



and



''; i = 56, 57

and 58) and nine equations (Equations (2-4); (8-13)),

there should be solutions for these variables. In this study,

a calculation [9] to solve these equations was followed,

in which exponential approximation is used. Finally, a

fractionation degree of the unknown sample, δ56Fe

(Equation (1)) can be determined.

The spike calibration method is as follows. First, the

pure spike is measured. In this study, the averages of

the pure spike isotope ratios, Rspike'-i/54 (i = 56, 57 and 58)

are obtained to be 25.927, 52.110 and 58.973, respec-

tively. Then, mixtures of the spike and the standard,

IRMM-014 were prepared and measured. Then, the spike

isotope ratio of Rspike-56/54 and



' are determined to mini-

mize the difference between the 56Fe/54Fe ratio of

IRMM-014 and the average of the 56Fe/54Fe ratio ob-

tained from the double spikes calculation using Micro-

soft-Excel “Solver”.

In the actual sample measurement, the spike-sample

mixture is bracketed by the spike-standard mixture. Then

from all the spike-standard isotope ratios, the average of

Rspike-56/54 and the optimum



' in one session are obtained.

Then the 56Fe/54Fe ratios of the sample and the standard

before and after the sample measurement are calculated.

Finally, δ56Fe of each sample is determined. In this cal-

culation, the typical error of 56Fe/54Fe of the standard

solution was 0.06‰ (SD).

3. Results and Discussion

3.1. Kinetic Effects in Adsorption of Fe

For the TEVA resin, kinetic effects in adsorption of Fe

are not negligible [5]. Therefore, the kinetic effects in the

adsorption of Fe were examined. The Fe standard solu-

tions were loaded on the TEVA column with adsorption

time of 5, 10, 25 and 55 min. Then Fe was collected, and

the yields were measured.

Analytical results are shown in Figure 1. The recovery

of Fe was ~100% after 5 min. However, the recovery

yields of >5 min seem a bit lower than 100%. Therefore,

the optimal adsorption reaction time is determined as 5

min. When the adsorption reaction time becomes longer

than 5 min, some Fe ion cannot be desorbed from the

resin by 6.4 mL of 2 mol·L−1 HNO3.

3.2. Elution Curves of Fe in the TEVA Column

An elution curve of Fe of the TEVA column is shown in

Figure 2. In the figure, only Mg and Fe are plotted, how-

ever, other major elements in silicate samples such as Na,

Al, P, Ca, Cr, Mn and Ni behave similarly to Mg. As

shown in Figure 2, almost 100 % of major elements in

100

0 102030405060

Recovery yi eld (%)

Time

(

min

)

Figure 1. The sample adsorption time (min) after sample

loading vs. the recovery yield (%). Error bars are the quan-

titative analytical error of ~7%. The dotted horizontal line

shows 100% yield.

0.1

100

02468

Fraction (%)

LFe fracti on

Eluent

(

)

Wash

Figure 2. Elution curves of Fe and Mg for the TEVA col-

umn. Mg represents behaviors of Na, Al, P, K, Ca, Cr, Mn,

Fe, Co and Ni. The horizontal axis shows total eluent vol-

ume (mL). The vertical axis indicates fraction (%) recov-

ered from each eluent fraction (%) compared to the added

amounts on the column. The vertical axis is in the logarith-

mic scale. The horizontal arrows at the top show the eluents

for wash and Fe fraction, respectively. “L” indicates the

sample loading solution.

silicate samples added in the column are washed away in

the first 1.6 mL of 6 mol·L−1HCl with H2O2. The total

yield of Fe using actual silicate samples was 93.5 ±

6.5 % (SD). This result means that there could be a small

loss of Fe in this study. Such loss of Fe could cause iso-

topic fractionation [18]. However, such fractionation can

be corrected by the double spike method employed in

this study.

Zinc, Ga, Nb, Mo, Ta, W and U were contained in the

Fe fraction with yields of 60% - 90%. However, in usual

silicate samples, amounts of these elements compared to

1 μg Fe are <ng levels, therefore, effects of these impuri-

ties are inconsequential. Furthermore, total yields of Nb,

Ta and W from the sample solution should be lower than

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A. MAKISHIMA

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those of the starting solution, because co-precipitation

with Ti oxides of Nb, Ta and W should occur during

sample evaporation using HClO4 [19].

The total blanks including sample digestion were 6 ng

(n = 6). As δ56Fe range of all natural samples is <±3‰

[7], δ56Fe of blank can be assumed to be <±3‰. Since Fe

in the sample is 1 μg, the maximum shift of δ56Fe by the

blank should be <±0.02‰. As the repeatability of the

standard solution was found to be 0.06‰, the blank ef-

fects are less than one thirds of the repeatability of the

standard solution. Thus the blank effect can be neglected.

3.3. Evaluation of Accuracy in Fe Isotope Ratio

Measurement

It is difficult to evaluate the accuracy in stable isotope

mass spectrometry for less popular elements such as Fe,

because the standard materials with accurate isotope ra-

tios are limited. In this study, to examine the accuracy

with variable isotope ratios and matrix elements, the

synthesized samples were made by mixing of two sam-

ples with different isotope ratios and matrix element

compositions. Then the isotope ratios of the mixture were

compared with the calculated isotope ratios. Such mixing

tests were done in studies of Zn and Tl isotopes to evalu-

ate the accuracy of the method [4,20].

For one sample, one of the JB-2 solutions of δ56Fe =

−0.27 ± 0.03 (see the next section) was used. For the

other sample, one of ferruginous bodies-digested solu-

tions [21] of δ56Fe = −3.16 ± 0.09 (n = 4) (private com-

munication, Makishima and Nakamura, Okayama Uni-

versity, Dec. 2012) was used. This solution was prepared

by ashing the ferruginous bodies separated from human

lung and dissolving with nitric acid. This solution has a

very low δ56Fe value, and is mostly composed of Fe [21].

The JB-2 and ferruginous bodies-digested solutions were

taken and mixed to contain 1 μg of Fe. Three types of the

mixtures with different matrix compositions were made.

For each type of the mixtures, four or five samples were

made. Each sample was added with 0.4 mL 6 mol·L−1

HCl and the Fe double spike, dried and passed through

the TEVA column. Then Fe was collected and its isotope

ratio was determined by MC-ICP-MS.

Analytical results of the δ56Fe value of each mixture

are shown in Table 3. The calculated values are also

shown in Table 3 . The error in calculation for each mix-

ture was based on concentration error of ~5% of two

starting solutions, and no other errors are taken into ac-

count. From Table 3, the observed values are consistent

with the calculated values within 2SD ranges, although

the three samples had different major element composi-

tions. Therefore, it is suggested that the double spike

method for Fe isotope measurements using MC-ICP-MS

in this study gives accurate isotope ratios of Fe.

3.4. Fe Isotope Ratio Measurements in Silicate

Reference Materials

The TEVA column chemistry developed in this study

was applied to analysis of the silicate reference materials,

and analytical results are presented in Table 4, together

with the reported values [11,22-26]. To make the com-

parison between δ56Fe of this study and those of refer-

ences easier, they are plotted in Figure 3. The δ56Fe

value of BHVO-1 in this study of 0.18‰ is a little higher

than those of references [22-24,26]. The δ56Fe values of

AGV-1 and PCC-1 of this study are −0.10 and 0.00‰,

respectively, which are consistent with those of previous

studies [21,25,26] when errors are taken into account.

Repeatability for silicate reference materials (Table 4)

is 0.03‰ - 0.06‰, and the average is 0.05‰. This

0.05‰ should be considered as repeatability of actual

silicate analysis by MC-ICP-MS in this study. As dis-

cussed previously, the blank effects are ±0.02‰, how-

ever, this can be negligible to 0.05‰, which is consid-

ered to be repeatability of this method. This value is

similar to that of the pure standard solution (0.06‰).

The repeatability in the Fe standard solution is com-

pared with those of references here. The SD values of

replicate analyses of the standard solution are 0.013, 0.10,

0.010, 0.050 and 0.041‰ in Chicago [22], Woods Hole

[23], Hannover [24], Madison [25], and Frankfurt [26]

groups, respectively. Therefore the repeatability of the

MC-ICP-MS methods of these leading groups which use

the bracketing method is similar or a bit better than that

of this study. However, all groups use AG 1X8, so they

need repetitive column chemistry in many cases, because

Fe cannot be purified enough by the single column

chemistry to be used in the mass spectrometry. However,

other groups [11] which use AG MP-1 can purify Fe by a

single column chemistry.

Recently, Millet et al. [11] achieved “ultra-precise” Fe

measurements, using the same pair of the double spike,

57Fe-58Fe. They constantly achieved the repeatability of

Table 3. Analytical results of mixing experiments.

Calculated Observed

　δ56Fe SD (‰) δ56Fe SD (‰) n

Mixture#1 −1.12 0.08 −1.36 0.04 4

Mixture#2 −1.90 0.13 −2.00 0.19 4

Mixture#3 −2.50 0.17 −2.64 0.05 5

A. MAKISHIMA

100

Table 4. δ56Fe values of USGS and GSJ silicate reference materials and carbonaceous chondrites.

Sample Average SD n References

δ56Fe (‰) (Error is SD)

BHVO-1 0.18 0.03 3 0.105 ± 0.008 [22], 0.110 ± 0.060 [23], 0.109 ± 0.024 [24], 0.117 ± 0.015 [26]

AGV-1 −0.10 0.06 3 0.04 ± 0.01 [24]

PCC-1 0.00 0.02 3 0.025 ± 0.012 [22], −0.06 ± 0.06 [25], 0.043 ± 0.013 [26]

JB-1 −0.14 0.05 4

JB-2 −0.27 0.03 4 0.073 ± 0.014 [11]

JB-3 −0.35 0.08 3

JA-1 −0.13 0.06 4 0.060 ± 0.010 [11]

JA-2 −0.02 0.03 4

JA-3 0.09 0.06 4

JP-1 −0.54 0.06 4

Orgueil −0.05 0.06 3 −0.015 ± 0.074 [26], 0.38 [27], 0.04 ± 0.06 [28]

Murchison −0.10 0.12 3 −0.12 ± 0.06 [28]

Allende −0.03 0.03 3 −0.007 ± 0.012 [22], −0.04 [27], −0.06 ± 0.01 [28]

-0.4

-0.3

-0.2

-0.1

0.1

0.2

0.3

0.4

-0.4-0.3-0.2-0.100.1 0.2 0.3 0.4

Orgue il

Murchison

Al len de

BH VO-1

AGV - 1

PCC- 1

56Fe of references

56Fe of this study

Figure 3. Iron isotope ratios (δ56Fe) of this study vs. those of

references. The error bars show one standard deviation of

repeatability (SD, ‰). The vertical and horizontal dotted

lines show δ56Fe = 0 of this study and references, respec-

tively. The dotted slope line indicates slope = 1, which

means that there is no difference in δ56Fe between this study

and references.

0.01‰ using double-spike-MC-ICP-MS. The largest

difference of this study from their study is 1) enrichment

of the double spike and 2) larger usage of the sample.

The 56Fe/54Fe, 57Fe/54Fe and 58Fe/54Fe ratios of the spike

in this study are 24.5521, 53.0182 and 48.0436, while

those of their spike are 2031, 67300 and 6812, respec-

tively. This means that the denominator isotope, 54Fe of

this study is far more abundant than that or Millet et al.

[11], resulting in lower precision. In addition, Millet et al.

[11] used a 100 μL·min−1 nebulizer and 2 μg·mL−1 solu-

tion, totally 4 times larger amounts of Fe are used than

that in this study.

3.5. Application to Measurements of δ56Fe in

Carbonaceous Chondrites

The δ56Fe values of carbonaceous chondrites, Orgueil,

Murchison and Allende were measured by the method

developed in this study. The δ56Fe value of Orgueil of

this study agrees well with those of Weyer et al. [26] and

Kehm et al. [28], but that of Zhu et al. [27] seems a bit

higher. The δ56Fe values of Allende of this study also

agrees well with those of previous studies [22,27,28].

However, numbers of analyses of carbonaceous chon-

drites in literatures are limited, and carbonaceous chon-

drites could be heterogeneous, thus further studies are

required.

Interference ratios of 54Cr/54Fe and 58Ni/58Fe in these

carbonaceous chondrite analyses after the column chem-

istry were <1.6 × 10−3 and <1.4 × 10−4, respectively.

Large Cr and Ni corrections were needed in the TEVA

column chemistry developed in this study, however, the

analytical results suggest that the single-pass TEVA

column is sufficient even in analyses of Cr rich samples

such as peridotites (~3000 μg·g−1) or chondrites (~4000

μg·g−1).

4. Conclusions

Using an extraction resin, TEVA, new column chemistry

for separating Fe has been developed for Fe isotope ratio

determination by MC-ICP-MS. Iron was purified by 6

mol· L −1 HCl + H2O2, and major elements were separated.

Fe was finally recovered with 2 mol·L−1 HNO3. The re-

covery yields and total blanks were 93.5% ± 6.5% (SD)

and 6 ng, respectively.

For evaluation of the separation method, Fe isotope ra-

tios were measured by a double spike method using

MC-ICP-MS, respectively. Repeatability obtained from

actual analyses of USGS standard reference materials of

Open Access IJAMSC

A. MAKISHIMA 101

BHVO-1, AGV-1, PCC-1, and GSJ standard silicate ma-

terials of JB-1, JB-2, JB-3, JA-1, JA-2 and JA-3 were

0.05‰ (SD). Fe isotope ratios of carbonaceous chon-

drites of Orgueil, Murchison and Allende were also de-

termined by the column chemistries developed in this

study.

5. Acknowledgements

The author thanks to E. Nakamura for suggestions and

supports at various aspects of this study. The author is

also grateful to K. Tanaka for doing column chemistry;

and T. Moriguti, C. Sakaguchi and all members of PML

for maintaining the clean laboratory. The author is also

grateful to K. Okabe for donating ferruginous protein

bodies.

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