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Separation of high field strength elements
(Nb, Ta, Zr, Hf ) and Lu from rock samples for
MC-ICPMS measurements
Carsten Mu¨ nker, Stefan Weyer, Erik Scherer, and Klaus Mezger
Zentrallabor fu¨r Geochronologie, Mineralogisches Institut, Universita¨t Mu¨nster, Corrensstr. 24, 48149 Mu¨nster,
Germany (muenker@nwz.uni-muenster.de; weyer@ThermoFinniganMAT.de; escherer@nwz.uni-muenster.de;
klaush@nwz.uni-muenster.de)
[1] Abstract: The application of multiple collector inductively coupled plasma source mass
spectrometry (MC-ICPMS) to
176
Lu-
176
Hf and
92
Nb-
92
Zr chronometry has been hampered by complex
Zr-Hf purification procedures that involve multiple ion exchange column steps. This study presents a
single-column separation procedure for purification of Hf and Lu by ion exchange using Eichrom
1
Ln-
Spec resin. The sample is loaded in pure HCl, and element yields are not dependent on the sample
matrix. For
92
Nb-
92
Zr chronometry, a one-column procedure for purification of Zr using Biorad
1
AG-
1- 8 resin is described. Titanium and Mo are completely removed from the Zr, thus enabling accurate
92
Zr measurements. Zirconium and Nb are quantitatively separated from rock samples using Eichrom
Ln-Spec resin, allowing measurements of Zr/Nb with a precision of better than ±5% (2s). The Ln-Spec
and anion resin procedures may be combined into a three-column method for separation of Zr-Nb, Hf,
Ta, and Lu from rock samples. For the first time, this procedure permits combined isotope dilution
measurements of Nb/Ta, Zr/Hf, and Lu/Hf using a mixed
94
Zr-
176
Lu-
180
Hf-
180
Ta tracer. Analytical
protocols for Zr and Hf isotope measurements using the Micromass Isoprobe, a second generation,
single-focusing MC-ICPMS, are reported. Using the Isoprobe at Mu¨nster, 2s external precisions of
±0.5e units for Hf and Zr isotope measurements are achieved using as little as 5 ng (Hf) to 10 ng (Zr) of
the element. The
176
Hf/
177
Hf and Lu/Hf for rock reference materials agree well with other published
MC-ICPMS and thermal ionization mass spectrometry (TIMS) data.
Keywords: Separation; Ln Spec; zirconium; hafnium; niobium; tantalum.
Index terms: Isotopic composition/chemistry; instruments and techniques; trace elements; geochronology.
Received May 17, 2001; Revised September 28, 2001; Accepted September 28, 2001; Published December 14, 2001.
Mu¨nker, C., S. Weyer, E. Scherer, and K. Mezger, Separation of high field strength elements (Nb, Ta, Zr, Hf ) and Lu from
rock samples for MC-ICPMS measurements, Geochem. Geophys. Geosyst., 2, 10.1029/2001GC000183, 2001.
1. Introduction
[2] The advent of multiple collector inductively
coupled plasma source mass spectrometry (MC-
ICPMS) has facilitated high-precision isotope
ratio measurements of the high field strength
elements (HFSE:Zr-Hf-Nb-Ta) [e.g., Blichert-
Toft et al., 1997; Mu¨nker et al., 2000; Sanloup et
al., 2000; Hirata, 2001]. In contrast to thermal
ionization mass spectrometry (TIMS), where
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Published by AGU and the Geochemical Society
AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES
Geochemistry
Geophysics
Geosystems
Technical Brief
Volume 2
December 14, 2001
Paper number 2001GC000183
ISSN: 1525-2027
Copyright 2001 by the American Geophysical Union
the high first ionization potentials of HFSE
necessitate the use of a large amount of sample
material (typically >1mg of the element), the
plasma source of MC-ICPMS instruments ion-
izes the HFSE with greater efficiency, so that
external precisions of approximately ±0.5 epsi-
lon units can be achieved for less than 100 ng of
the element.
[3] Zirconium and Hf are particularly interest-
ing because they include the radiogenic daugh-
ters of the
176
Lu-
176
Hf (half-life = 37.17 Ga
[Scherer et al., 2001]) and
92
Nb-
92
Zr chronom-
eters (half-life = 36 Ma [Nethaway et al.,
1978]). Accurate
176
Hf and
92
Zr measurements
require removal of the interfering
176
Yb,
176
Lu,
and
92
Mo. Moreover, the separation from
whole rock matrices is necessary because the
precision of MC-ICPMS data is adversely
affected by (1) formation of interfering polya-
tomic species in the plasma and (2) matrix-
dependent change of mass bias behavior. The
influence of Ti on mass fractionation processes
during Hf and Zr isotope ratio measurements,
first noticed for Hf by Blichert-Toft et al.
[1997], is shown in Figure 1. Owing to its high
abundance in silicate rocks relative to Zr and
Hf, Ti may cause significant shifts in measured
Zr and Hf isotope ratios. Titanium behaves like
Zr and Hf during cation and anion separations
[Korkisch, 1989]; thus additional purification
of Zr and Hf is required.
[4] Isotope dilution enables the precise meas-
urement of Zr/Hf and Nb/Ta ratios, which in
most terrestrial rocks apparently scatter by
about ±30% around the chondritic ratios of
34.5 and 17.6, respectively [e.g., Eggins
et al., 1997; Jochum et al., 1996; Mu¨nker,
1998; Niu and Batiza, 1997; Plank and White,
1995; Stolz et al., 1996; Weyer et al., 2001].
Such small natural ranges preclude measure-
ments of Zr/Hf and Nb/Ta at sufficient resolu-
tion using externally calibrated methods such
as quadrupole ICPMS, X-Ray Fluorescence
(XRF), or Instrumental Neutron Activation
Anaylsis (INAA), which have typical external
precisions and accuracies for these ratios of no
better than ±10%. Measurement of Zr/Hf and
Nb/Ta by isotope dilution is therefore the most
promising method for resolving natural varia-
tions of Zr/Hf and Nb/Ta. Although Nb is
mono-isotopic and cannot be measured by
isotope dilution, a
180
Ta tracer [Weyer et al.,
2001] now permits much more precise Nb/Ta
measurements. The approximately ±5% accu-
racies of the first Zr/Hf isotope dilution meas-
urements by ICPMS [David et al., 1999; Reid
et al., 1999; Xie and Kerrich, 1995] were
limited by the accuracy of spike calibration,
mode of mass bias correction, and instrument
sensitivity. These uncertainties can be reduced
to better than ±1% by removing the sample
matrix and improving the spike calibrations.
[5] Here we report ion exchange separation
procedures for the HFSE and protocols for Zr
and Hf measurements by MC-ICPMS that are
used at Mu¨nster. A new, one-column method
for rapid separation of Lu and Hf from whole
rock matrices is introduced. This procedure
also permits separation of Hf from almost any
matrix, including peridotites, garnets, and phos-
phates. With previous hydrofluoric acid-based
techniques, separation of Hf (and Zr) from
peridotites and phosphates was extremely dif-
ficult owing to (1) coprecipitation of HFSE
with Ca-Mg fluorides [Blichert-Toft, 2001]
and (2) the large amount of sample required
(up to several grams). We also report a new
one-column procedure for separating Zr from
rock matrices, Ti, and the interfering Mo.
2. Previous Separation Techniques
[6] The first routine Lu-Hf separation method
designed specifically for geologic samples was
introduced by Patchett and Tatsumoto [1980],
who combined elements of earlier separation
schemes [e.g., Benedict et al.,1954;Faris,
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1960] into a three-column procedure (cation
and anion resins). Other procedures based on
various combinations of cation and anion
exchange steps (three to four columns) were
subsequently developed [e.g., Salters and Hart,
1991; Salters, 1994; Barovich et al., 1995;
Scherer et al., 1995; Blichert-Toft et al., 1997;
Blichert-Toft and Arndt, 1999; Kleinhanns et
al., 2000; Blichert-Toft, 2001]. The pre-1997
methods were designed for TIMS or hot SIMS
analyses and thus required (1) handling of large
samples (up to several grams of rock) and (2)
1.5220
1.5240
1.5260
1.5280
1.5300
-2.5
ε
-16
ε
ca -40
ε
-6
ε
0±0.7
ε
80 ppb Hf solution
(no added Ti)
+1 ppm
Ti
10 ppm
Ti
+100 ppm
Ti
after
experiment
no Ti
176
177
Hf
Hf
/
50 ppb Zr solution
(no added Ti)
+1 ppm
Ti
+10 ppm
Ti
+100 ppm
Ti
after
experiment
no Ti
92
91
Zr
Zr
/
a)
b)
0.28206
0.28208
0.28210
0.28212
0.28214
0.28216
0.28218
Figure 1. The internally corrected (a)
92
Zr/
91
Zr and (b)
176
Hf/
177
Hf obtained for Zr-Hf standard solutions
(50 ppb) at different Ti abundances. Ti/Zr and Ti/Hf of greater than 10 in the analyte cause a bias of internally
corrected isotope ratios relative to those of the pure standard solutions. Likewise, pure standard solutions that
were measured immediately after the Ti-rich solutions gave systematically wrong values. This offset is most
likely caused by a change in mass fractionation processes during build-up of Ti in the cone-orifice region of
the MC-ICPMS.
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mu¨ nker et al.: separation of high field strength elements 2001GC000183
efficient Ti-Zr separation from Hf to maximize
ionization efficiency. In some methods, the
amount of sample matrix to be processed is
reduced by first leaching the digested rock
sample in HF to separate an HFSE-rich super-
natant from the precipitated REE-bearing bulk
matrix [Salters and Hart, 1991; Salters, 1994;
Barovich et al., 1995; Scherer et al., 1995;
Blichert-Toft et al., 1997]. For some rock
matrices, such leaching decreases Hf yields
dramatically (Hf is coprecipitated with Ca-Mg
fluorides), but leaching can be replaced by an
additional cation column step [Blichert-Toft,
2001]. Efficient Ti-Zr-Hf separation was
achieved using H
2
SO
4
[Barovich et al., 1995;
Scherer et al., 1995], in which distribution
coefficients between Ti-Zr-Hf differ signifi-
cantly [Danielson, 1965; Hague and Machlan,
1961; Strelow and Bothma, 1967]. In principle,
chemical separations for MC-ICPMS can be
simplified over previous methods because the
high ionization efficiency of the plasma source
(1) allows smaller samples to be run and (2)
eliminates the need for efficient Zr-Hf separa-
tion. In practice, however, extreme care must
still be taken to avoid significant isobaric
interferences (e.g.,
176
Yb and
176
Lu on
176
Hf )
and matrix effects (Figure 1). Recently, simple,
one-column Hf separation schemes based on
Eichrom TEVA Spec have been developed
[Yang and Pin, 1999; Le Fe`vre and Pin,
2001]. Although they permit the direct separa-
tion of Hf from the bulk sample matrix, neither
method provides a Lu fraction for ID analysis.
3. New Separation Procedures
3.1. Reagents and Digestion Procedure
[7] Once-distilled HF, HCl, and HNO
3
were
used throughout. Reagent grade acetic acid,
citric acid, and H
2
O
2
were used; their contri-
butions to HFSE blanks were negligible. Pro-
cedural blanks are <10 pg for Lu, <1 ng for Zr,
<100 pg for Hf, <100 pg for Nb, and <100 pg
for Ta. For demanding, low-blank applications,
blanks can be reduced to 10 pg for Hf and
300 pg for Zr by using HF and HCl that have
been distilled a second time in Teflon.
[8] Rock samples were digested in 1:1 HF-
HNO
3
. Except for basalts (1208 C tabletop
digestions), all samples were digested at
1808C in Savillex
1
vials placed inside Parr
1
bombs. Zircon-bearing samples were fused
with five parts Li
2
B
4
O
7
, dissolved in HCl,
and redigested in HF-HNO
3
to achieve full
sample-spike equilibration for the HFSE. After
evaporation, the samples were dried down 3
times in 2 mL of concentrated HNO
3
-trace HF
(<0.05 M ). The samples were then completely
dissolved in 8 –10 mL 6 M HCl-trace HF. No
precipitates were observed. Combining strong
HNO
3
or HCl with trace HF ensures sample-
spike equilibration. (Using only trace HF sta-
bilizes HFSE in solution without precipitating
Lu-fluorides.) The external reproducibility of
Lu/Hf ratios was better than ±1% (2s)for
multiple replicate rock digestions.
3.2. One-Column Zr Separation by Anion
Exchange
[9] The one-column procedure for Zr separation
(Table 1, Figure 2) is based on anion-exchange
chromatography using BIORAD AG-1-X8
resin (100–200 mesh, Cl
form). The Zr-Hf
distribution coefficients in HCl-HF on anion
resin depend little on HF molarity below 5 M
[Faris, 1960; Kim et al., 1973], but they are
extremely sensitive to the HCl molarity (>10 in
molarities lower than 2 M HCl [Kim et al.,
1973; Nelson et al., 1960; Wish, 1959]). The
column is therefore preconditioned in 2 col-
umn volumes (v) of 0.5 M HCl-0.5 M HF. After
centrifuging, the sample is loaded in 1 M
HCl-0.5M HF without a precipitation step, thus
avoiding coprecipitation of Zr with fluorides.
Typically, 100 mg of digested sample are first
dissolved in 1.5 mL 3 M HCl and then diluted
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to 4.5 mL with H
2
O. Upon complete disso-
lution, 0.5 mL of 6 M HF are added to
achieve a final concentration of 1 M HCl-
0.5 M HF. Higher loading volumes (5 mL or
more), especially for peridotites, are required to
keep larger samples in solution. Loading 100
mg of basaltic sample matrix in up to 40 mL of
1 M HCl-0.5 M HF gave >90% Zr yields. For
>200 mg peridotite samples, coprecipitation of
Zr with Ca-Mg-fluoride reduced the yields.
[10] After loading, the bulk matrix is eluted
with 0.5 M HCl-0.5 M HF, while the HFSE,
Mo, and W stay on the column [Kim et al.,
1973]. Titanium is eluted with a mixture of
acetic acid (HAc), HNO
3
, and H
2
O
2
because
the distribution coefficients for Ti in acetic acid
are much lower (1) than those for other HFSE
(>100 [van den Winkel et al., 1971]). Optimum
separation of Ti is achieved in a mixture of 3.6
M HAc-8 mM HNO
3
(Figure 2). Higher HNO
3
(and HCl) molarities (i.e., a decrease in pH)
lower the partition coefficients in acetic acid,
causing early elution of all HFSE at HNO
3
(and
HCl) molarities >0.1 [Kim et al., 1973]. For
this reason, 1.5 v of 0.5 mM HCl-0.5 mM HF
are passed before Ti is eluted.
[11] The Ti-Zr separation is less efficient at
lower HAc molarities (<2 M), but it is relatively
insensitive to the length of the resin bed (4–23
cm) and the amount of resin used (3–8 mL). If
>50 mg of Ti are loaded on the column, H
2
O
2
is
added to the HAc-HNO
3
mixtures (Figure 2b–
2c) to prevent hydrolysis of Ti on the column.
For mafic samples (1000 mg Ti per 100 mg
sample), 80% of the Ti would otherwise be
eluted with the Zr, resulting in unacceptably
high Ti/Zr in the Zr cut.
[12] After Ti elution, the column is equilibrated
with 1.5 v of H
2
O
2
-free 9 M HAc to prevent
elution of the remaining HFSE in H
2
O
2
-HCl-
HNO
3
mixtures. To minimize the isobaric inter-
ference of
92
Mo on
92
Zr, Zr-Mo separation is
achieved in 6 M HCl-0.06 M HF [Sahoo and
Table 1. Column Dimensions and Single-Column Separation Procedures for Zr, Lu-Hf
a
One Column
Lu-Hf
EICHROM Ln Spec
(1 mL, ca. 3.80.6 cm)
c
One Column
Zr
BIORAD AG-1-X8
(4 mL, ca. 8.70.8 cm)
Step Column
Volumes
Acid Step Column
Volumes
Acid
Load sample 5 v 3M HCl (+ 0.1M
ascorbic acid)
load sample 1.25 v 0.5 M HCl-0.5 M HF
Rinse matrix 10 v 3 M HCl rinse matrix 2.5 v 0.5 M HCl-0.5 M HF
HREE (Lu-Yb)
d
10 v 6 M HCl rinse matrix 0.5 + 0.5 + 0.5 v 0.5 mM HCl-0.5 mM HF
Washout HCl 2 + 2 v H
2
O Ti 2.5 15 v 3.6 M HAc-8 mM
HNO
3
-1% H
2
O
2
Ti variable 0.09 HCit-0.4N
HNO
3
-1 wt% H
2
O
2
washout H
2
O
2
1.5 v 9 M HAc
Washout H
2
O
2
5 v 0.09 HCit-0.4N HNO
3
Zr(+Hf )
b
2.5 v 6 M HCl-0.06 M HF
Zr 50 v 6 M HCl-0.06 M HF Mo-Nb
(optional)
5v 6M HNO
3
-0.2 M HF
Hf
b
12 v 6 M HCl-0.2 M HF cleaning 5 v 6 M HNO
3
-0.2 M
HF-1 wt % H
2
O
2
Cleaning 10 v
10 v
6 M HCl
2 M HF (alternating)
5v 1M HCl-1 mM DTPA
a
Here v refers to resin volumes. Note that all solutions containing H
2
O
2
need to be freshly prepared.
b
These particular element-cuts are collected for further analysis (as discussed in text).
c
Note that separation efficiency and yields decrease after the resin has been used about 15 times.
d
At high Lu/Hf, more 6 M HCl is required to remove all Lu.
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synthetic solution (10 µg Ti) without H
2
O
2
0
10
20
30
40
50
60
0 20406080100120
ml eluted
% eluted element
Ti
Zr
Hf
0.5N HCl/0.5N HF
5mM HCl/5mM HF
8mM HNO
3
/3.6M HAc
6N HNO3/0.2N HF
a)
Ti
Hf
Zr
basaltic matrix (1000 µg Ti) with H
2
O
2
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
ml eluted
% eluted element
Ti
Zr
Hf
0.5N HCl/0.5N HF
5mM HCl/5mM HF
8mM HNO
3
/3.6M HAc/
1%H
2
O
2
6N HNO
3
/0.2N HF
Ti
Zr
Hf
c)
basaltic matrix (1000 µg Ti) without H
2
O
2
0
20
40
60
80
100
120
0 20 40 60 80 100 120
ml eluted
% eluted element
Ti
Zr
Hf
0.5N HCl/0.5N HF
5mM HCl/5mM HF
8mM HNO
3
/3.6M HAc,
no H
2
O
2
6N HNO
3
/0.2N HF
Ti
Ti
Zr+Hf
b)
Figure 2. Elution schemes for Zr separation from a synthetic solution and a basaltic matrix using our anion
exchange chemistry. For high-Ti samples, the use of H
2
O
2
together with acetic acid (HAc) - nitric acid is
required to remove the Ti efficiently.
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Masuda, 1997; Wish, 1959], where a Mo-free
Zr-Hf (+some Nb) fraction is eluted in 2.5 v. The
Ti/Zr of the Zr-Hf fraction is typically 1(Ti
minerals, basalts) or lower (Ti-poor samples),
allowing sufficiently accurate Zr isotope meas-
urements (Figure 1). The Mo/Zr of the Zr cuts
were always <0.001. If needed, Mo and some of
the Nb can be eluted after Zr with 6 M HNO
3
-0.2
M HF [Huff, 1964]. Cleaning the column with a
sequence of 6 M HNO
3
-0.2 M HF-1% H
2
O
2
,1
mM DTPA-1 M HCl, and 3 M HNO
3
(4 v each)
removes all remaining HFSE, allowing multiple
use of the resin. Complexes of HFSE with F
or
DTPA (Diethylene-triamine-pentaacetic acid)
are efficiently eluted from anion resin at low
pH [Faris, 1960, and this study].
3.3. One-Column Lu-Hf Separation
Using EICHROM
#########
Ln-Spec
[13] Most previous methods of Hf separation
involve several column steps and are sensitive
to the amount of sample loaded, the sample’s
bulk composition, and the anionic speciation of
the solute [see Patchett and Tatsumoto, 1980;
Blichert-Toft, 2001]. Our new, matrix-independ-
ent, one-column separation procedure for Lu
and Hf (Figure 3, Table 1) is based on reversed
phase cation-exchange chromatography using
EICHROM Ln-Spec resin (100–150mm, H
+
form). EICHROM Ln-Spec resin consists of
an HDEHP (di (2-ethylhexyl) phosphoric acid)
coating on an inert polymeric carrier (Amber-
chrom CG71). HDEHP has long been used in
solvent/solvent extraction procedures between
aqueous and organic phases, where HDEHP is
dissolved in the organic phase (see Braun and
Ghershini [1975] for a review). In contrast to
HDEHP-coated Teflon (widely used for Sm-Nd
separations [e.g., Richard et al., 1976]), the
separation efficiency of Ln-Spec resin is rela-
tively insensitive to different sample matrices,
allowing direct loading of bulk digested sam-
ples in HCl. On Ln-Spec resin, HFSE have high
distribution coefficients in strong (>1 M) HCl,
in marked contrast to most other major and trace
elements [Braun and Ghershini, 1975; Vin and
Khopkar, 1991; M. Langer, personal communi-
cation, 2000, and this study]. At HCl molarities
<4, Lu and Fe
3+
are co-adsorbed with the
HFSE. However, Fe
3+
shows minimum adsorp-
tion at 3 M HCl [Braun and Ghershini, 1975],
making this the ideal molarity for loading bulk
rock samples without overloading the column
with Fe.
[14] For accurate Lu ID measurements, the
large isobaric interference of
176
Yb on
176
Lu
necessitates at least partial separation of Yb
from Lu. This separation has been achieved
using HDEHP [e.g., Braun and Ghershini,
1975; Lahiri et al., 1998] and can also be
accomplished on Ln-Spec resin in 2–4 M
HCl (Figure 4). With increasing HCl molarity,
Lu yield decreases, but Yb-Lu separation
increases. A good compromise between Lu
recovery (20–30%) and Lu-Yb separation
(i.e., a decrease of Yb/Lu by a factor of 5)
occurs with 3 M HCl.
[15] High field strength elements have low
distribution coefficients with Ln-Spec in 2 M
HF [Vin and Khopkar, 1991; M. Langer, per-
sonal communication, 2000; and this study].
HF is therefore a suitable elution media for
HFSE. HF also prevents the hydrolysis of
HFSE on the column. In HCl-HF mixtures,
adsorption behaviors differ among the HFSE.
Salters [1994] separated Zr from Hf on
HDEHP-coated Teflon with 6 M HCl-0.15 M
HF. Our experiments with Ln-Spec showed that
the separation factor is extremely sensitive to
HF molarity but relatively insensitive to HCl
molarity. Optimum Zr-Hf separation is
achieved in 6 M HCl-0.06 M HF. No Zr or
Hf is eluted at HF molarities below 0.03,
thereby defining the maximum HF-tolerance
level in sample loads. In 6 M HCl-0.2 M HF,
Zr and Hf are completely eluted, while 60–
80% of the Ta is retained on the column.
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basaltic matrix
0
20
40
60
80
100
120
0 50 100 150
ml eluted
% eluted element
Ti
Zr
Hf
Lu
load
3N HCl
Ti
Zr
Hf
Lu
HCit/HNO
3
/H
2
O
2
6N HCl
6N HCl/0.06N HF
6N HCl/
0.2N HF
a)
garnet matrix
0
20
40
60
80
100
120
0 50 100 150 200
ml eluted
% eluted element
Ti
Zr
Hf
Lu
Hf
ZrTi
Lu
load
3N HCl
6N HCl
HCit/HNO
3
/H
2
O
2
6N HCl/
0.06N HF
6N HCl/0.2N HF
c)
apatite matrix
0
20
40
60
80
100
120
0 50 100 150
ml eluted
% eluted element
Ti
Zr
Hf
Lu
load
3N HCl
6N HCl 6N HCl/0.06N HF
6N HCl/0.2N HF
Lu
Ti
Zr
Hf
b)
peridotite matrix
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200
ml eluted
% eluted element
Ti
Zr
Hf
Lu
load
3N HCl
6N HCl
6N HCl/0.06N HF
6N HCl/0.2N HF
Lu
Ti
Zr
Hf
HCit/HNO
3
/H
2
O
2
d)
Figure 3. One-column separation of Lu and Hf. Eichrom Ln-Spec elution profiles are shown for (a) a basalt sample, (b) a peridotite sample, (c)
apatite, and (d) garnet. For apatite, the Ti elution step is unnecessary. Column yields and separation efficiencies are not dependent on the rock
matrix.
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[16] On the basis of Patchett and Tatsumoto
[1980], we explored the partitioning behavior
of Ti, Zr, and Hf on Ln-Spec resin in mixtures
of HNO
3
, citric acid (HCit), and H
2
O
2
.In
contrast to their behavior on AG50W-X8 cation
resin, all HFSE stick as citrate complexes to
Ln-Spec resin in 0.09 M HCit and 0.45 M
HNO
3
. By adding H
2
O
2
to this mixture, Ti is
selectively eluted as an orange peroxide com-
plex, while Zr and Hf remain on the column.
The amount of HCit-HNO
3
-H
2
O
2
that is
needed (typically 30 v per mg Ti) increases
with the amount of Ti present and decreases
with HNO
3
molarity (minimum at 0.1 M).
With increasing HNO
3
molarity, more Nb and
Ta are co-eluted with Ti.
[17] For the single-column Lu-Hf chemistry
(Figure 3 and Table 1), a typical 100 mg sample
is loaded in 5mLof3M HCl. The sample
must be essentially HF-free (i.e., HF molarity
of <0.03). Fe-rich samples are loaded in 3 M
HCl-0.1 M ascorbic acid, in which Fe is
reduced to Fe
2+
and passes through the column.
Peridotite samples are typically loaded in 10–
20 mL 2 M HCl-0.05 M ascorbic acid, where,
in contrast to 3 M HCl, sufficient Lu is retained
on the column. Rinsing with 10 v of 3 M HCl
removes most matrix elements while leaving
behind a HREE fraction (Lu + Yb ± Tm). This
fraction is eluted in 6 M HCl. Titanium is then
eluted with 10–50 v of 0.09 M HCit-0.45 M
HNO
3
-1 wt.% H
2
O
2
. To avoid partial loss of
the HFSE in HCl-H
2
O
2
mixtures, the column is
rinsed with H
2
O before the Ti elution and with
H
2
O
2
-free 0.09 M HCit-0.45 M HNO
3
after the
Ti elution. Next, Nb and most of the Zr are
eluted in 50 v of 6 M HCl-0.06 M HF and Hf
is subsequently eluted in 6 M HCl-0.2 M HF.
The Zr/Hf in the Hf cut is decreased from 35
to 1. Hafnium yields are typically >95% and
are largely independent of the bulk matrix
composition (Figure 3). Individual elution
schemes for phosphates, garnets, and perido-
tites are shown in Figure 3.
3.4. Combined Separation of Lu, Zr-Nb,
Hf, and Ta
[18] The Lu, Zr-Nb, Hf and Ta separation
scheme (Table 2) combines our procedures
for the Zr and Hf separations. Because no
isotopic tracer for Nb exists, Nb and Zr (+Ti)
are quantitatively recovered from the sample.
1 2 3 4 5
HCl molarity
0
2
4
6
8
10
12
14
Yb/Lu in
HREE cut
a)
basalt BB
Yb/Lu ca. 8
1 2 3 4 5
HCl molarity
0
10
20
30
40
50
60
yields
(%)
b)
Yb
Lu
Figure 4. Dependence of the Ln-Spec Yb-Lu separation on the HCl molarity that is used for loading of the
sample. (a) Optimum separation is achieved at HCl molarities between 3 and 3.5. (b) Both Yb and Lu yields
decrease with increasing HCl molarity. At 3 N HCl, the Lu yield is 20%, which, in most cases, is still
sufficiently high for isotope dilution measurements.
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The absence of Cr in the Ti-Zr-Nb cuts rules
out any systematic error caused by the possible
53
Cr
40
Ar interference on
93
Nb; so Nb can be
measured as Zr/Nb, using the Zr concentration
obtained by isotope dilution. In contrast to
earlier anion exchange methods, where some
Zr is coprecipitated during the HF-based load-
ing procedure, a fully quantitative Zr-Nb recov-
ery is achieved using Ln-Spec. To correct for
the
180
Hf interference on
180
Ta, which only has
a natural abundance of 120 ppm relative to
181
Ta, a virtually complete separation of Hf
from Ta is needed. This is particularly impor-
tant if a combined
180
Ta-
180
Hf tracer is used.
[19] Three column steps are required for the
combined separation procedure (Table 2). Col-
umn I and III are identical to the Ln-Spec Hf
column and column II is an anion column.
After loading the sample and rinsing in 3 M
HCl, Lu is eluted in 6N HCl. A complete HFSE
fraction (Ti-Zr-Nb-Hf-Ta) is then eluted with
12 v of 2 M HF. This cut contains virtually all
of the Zr and Nb in the sample, thus permitting
direct measurements of Zr/Nb. After the
optional removal of a 10–20% aliquot from
the HFSE fraction for Zr/Nb measurements, the
remaining solution is loaded directly onto col-
umn II (BIORAD AG-1-X8). In 2 M HF, all
HFSE are retained on the column [Faris,
1960]. A fraction containing Ti-Zr-Nb-Hf is
subsequently eluted with 12 v 6 M HNO
3
-0.2
M HF while Ta remains on the column [Huff,
1964]. Complete Hf-Ta separation is accom-
plished by repeated rinsing with 6 M HNO
3
-0.2
M HF (Table 2). The Ta fraction is best eluted
with 12 mL of 6 M HNO
3
-0.2 M HF-1 wt.%
H
2
O
2
. After the Ti-Zr-Nb-Hf cut from column
Table 2. Three-Column Separation Procedure for Combined Separation of Lu, Hf, Ta, and a Quantitatively
Recovered Zr-Nb Fraction
a
Three column Lu-HFSE Ln Spec (1mL, ca. 3.80.6 cm) AG-1-X8 (4 mL, ca. 8.70.8 cm)
Step Column Volumes Acid
Column I (Ln Spec)
Load sample 5 v 3 M HCl
Rinse matrix 10 v 3 M HCl
HREE (Lu-Yb)
b
10 v 6 M HCl
Ti-Zr-Hf-Nb-Ta
b, c
12 v 2 M HF
Column II (AG-1- 8)
Load Ti-Zr-Hf-Nb-Ta cut 2.5 v 2 M HF
Rinse 2.5 v 2 M HF
Ti-Zr-Hf (Nb)
b
1+1+1 v 6 M HNO
3
-0.2 M HF
Rinse remaining Hf 4 v 6 M HNO
3
-0.2 M HF
Ta
b
1.5+1.5 v 6 M HNO
3
-0.2 M HF-1 wt % H
2
O
2
Column III (Ln Spec = Column I)
Load Ti-Zr-Hf (Nb) 5 v 3 M HCl
Rinse 10 v 6 M HCl
Washout HCl 2+2 v H
2
O
Ti Variable 0.09 HCit-0.4N HNO
3
-1wt % H
2
O
2
Rinse H
2
O
2
5 v 0.09 HCit-0.4N HNO
3
Zr 50 v 6 M HCl-0.06 M HF
Hf
b
12 v 2 M HF
a
Here v refers to resin volumes. Note that all solutions containing H
2
O
2
need to be freshly prepared.
b
These particular element-cuts are collected for further analysis (as discussed in text).
c
2 mL Zr/Nb aliquot, 10 mL are directly loaded onto column II.
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II is evaporated down, it is dissolved in 3 M
HCl and loaded onto column III (identical to
Ln-Spec column I). Titanium is again eluted as
an orange peroxide complex in 0.09 M HCit-
0.45 M HNO
3
-1 wt.% H
2
O
2
. Following Zr-Nb
elution in 50 v of 6 M HCl-0.06 M HF, a clean
Hf fraction is recovered in 2M HF.
[20] Accuracy and precision of the Zr/Nb ratios
were tested by replicate digestions and Zr/Nb
analyses of reference materials (Figure 5). Zr/
Nb was measured at a typical internal precision
of ±0.1% (2s) by MC-ICPMS against a stand-
ard prepared from 99.9% pure AMES Zr and
Nb metals. Better than ±5% (2s) external
precision was obtained for multiple digestions
of peridotite and basalt samples. To measure
HFSE yields, low-HFSE samples (e.g., perido-
tites) were doped with our mixed AMES HFSE
standard (Zr-Nb-Hf-Ta) so that their HFSE
concentrations were known to better than
±1%. The Ti-Zr-Nb cuts from these samples
were spiked with the mixed HFSE tracer, and
Zr-Nb concentrations were measured as
described. Zirconium and Nb yields were
>98% for basalts (100 mg samples) and
>90% for peridotites (1 g samples) (Table 3),
demonstrating nearly quantitative recovery for
Zr and Nb.
4. Zr and Hf Isotope Measurements
by MC-ICPMS
[21] The Micromass Isoprobe at Mu¨nster is a
new, second generation ICP-source magnetic
sector mass spectrometer with a multiple col-
lector configuration (nine Faraday collectors,
four channeltron ion counters, and a Daly ion
counter, Table 4). Elements having high first
24
26
28
3.0
3.2
3.4
3.6
basalt BB
Zr/Nb=3.29±4%
USGS BIR-1
Zr/Nb=25.2±2%
Zr/Nb
Figure 5. Zr/Nb obtained for different digestions of the rock standards USGS BIR-1 (14 ppm Zr, 0.55 ppm
Nb) and BB (in-house standard; 192 ppm Zr, 58 ppm Nb) after separation of a Ti-Zr-Nb cut using Ln-Spec
resin. Zr/Nb can be measured at an external precision of better than ±5% (2s) against a Zr/Nb standard that
was prepared from 99.9% pure AMES metals.
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ionization potentials, such as Zr and Hf, are
ionized at much higher efficiencies than with
thermal ionization mass spectrometers (TIMS).
In contrast to all other MC-ICPMS instru-
ments, which require an electrostatic analyzer
before the magnetic sector, the Isoprobe is a
single-focusing mass spectrometer, wherein a
hexapole collision cell reduces the energy
spread of the extracted ions from 20–30 V
to 1 V. Argon (1.2 mL/min) is typically
used as the collision gas for masses >40. A
Cetac MCN-6000 desolvating nebulizer yields
higher sensitivities than those achieved with
conventional glassware systems. Isotope com-
position measurements can be routinely per-
formed on as little as 5 ng (200 amu mass
range) to 10 ng (100 amu mass range) of the
element with typical external precisions of
better than 50 ppm.
[22] During the measurement period (late
1999–2001), the Isoprobe has operated at an
abundance sensitivity of 10–15 ppm (U), cor-
responding to an analyzer vacuum of 2
10
8
mbar. Peak tails on
181
Ta were 50–70
ppm at mass 180.5 and 16 ± 2 ppm for 181.5.
For Hf measurements, this abundance sensitiv-
ity level precludes baseline measurements at
half masses between peaks, which would result
in 100–200 ppm shifts for measured Hf iso-
tope ratios (Table 5). Hence baselines were
measured at half masses below the Hf isotope
array (i.e., at masses 168.5–172.5 for masses
176–180). Baseline tests at other half mass
arrays located both below and above the Hf
array gave Hf isotope compositions that are
indistinguishable from the ‘‘off-array’’ values
(Table 5). Owing to the wider distance between
the Zr peaks (masses 90–96), Zr baselines at
Table 3. Recovery of HFSE for a Doped Basalt, a Doped Peridotite Matrix, and Pure AMES Metal
Standard Using Eichrom Ln-Spec
a
Basalt BIR-1
(100 mg, Doped)
Peridotite BP7-Pe
(1 g, Doped)
Mixed Shelf
Yields in percent
Zr 98 93 -
Hf 91 80 -
Nb 101 89 -
Ta 91 84 -
Deviation in percent
Zr/Nb 3+4+1
a
Concentrations of HFSE in the doped samples were known to better than ±1%.
Table 4. Cup Configurations for Zr and Hf Isotope Measurements Using the Micromass Isoprobe in
Mu¨nster
Configuration L3 L2 (L1)Ax H1 H2 H3 H4 H5 H6
Zr-1 87 Sr
(Rb)
88 Sr 90 Zr 91 Zr 92 Zr
(Mo)
93 Nb 94 Zr
(Mo)
95 Mo 96 Zr
(Mo, Ru)
Zr-2 90 Zr 91 Zr 92 Zr
(Mo)
93 Nb 94 Zr
(Mo)
95 Mo 96 Zr
(Mo, Ru)
97 Mo 99 Ru
Hf 173 Yb 175 Lu 176 Hf
(Yb, Lu)
177 Hf 178 Hf 179 Hf 180 Hf
(Ta, W)
181 Ta 182 W
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half masses are not significantly affected by
tails. The most critical interferences for Zr and
Hf isotope measurements are listed in Table 6.
Because the mass bias of the Isoprobe MC-
ICPMS (0.5% at >200 amu and 2.5% at 100
amu) is typically 10 times higher than that of
TIMS (0.1%), we apply a mass bias correction
to the interference correction ratios (see Figure
6, Zr). In contrast to instruments equipped with
an electrostatic analyzer, mass bias in the Iso-
probe not only depends on the cone interface
but also varies with hexapole parameters and
Table 5. Isotopic Compositions Obtained for Zr (AMES Metal) and Hf (AMES Metal, Isotopically
Indistinguishable From JMC-475) Compared to Literature Values
a
Method Author(s)
91
Zr/
90
Zr
92
Zr/
90
Zr
96
Zr/
90
Zr
TIMS Minster and Alle`gre [1982] 0.21799 0.33338 0.054390
Nomura et al. [1983] 0.21819 0.33339 0.054474
Harper [1996] 0.21797 0.33337 0.054381
Sahoo and Masuda [1997] 0.21798 0.33336 0.054386
MC-ICPMS Hirata [2001] 0.21797 0.33341 0.054373
Sanloup et al. [2000] 0.21798 0.33341 0.054333
Yin et al. [2000] 0.21800 0.33338 0.054376
Rehka¨mper et al. [2001] - 0.33338 -
this study 0.21795 0.33339 0.054347
Method Author(s)
176
Hf/
177
Hf
178
Hf/
177
Hf
180
Hf/
177
Hf
TIMS Patchett and Tatsumoto [1980] 0.282195 - 1.88651
Patchett [1983a, 1983b] 0.282142 1.46710 1.88651
Nowell et al. [1998] 0.282155 - -
Scherer et al. [2000] 0.282165 1.46717 1.88679
Hot-SIMS Salters [1994] 0.282207-37 1.46714 -
MC-ICPMS Blichert-Toft et al. [1997] 0.282160 1.46717 1.88667
Halliday et al. [2000] 0.282161 - -
this study (half mass baseline) 0.282126 1.46743 1.88699
this study (off array baseline) 0.282151 1.46718 1.88652
a
Hf isotope values obtained using the Isoprobe (cup efficiencies set to unity) agree well with literature values if baselines are measured
outside the Hf array. All Zr isotope ratios (including values from other laboratories) are normalized to
94
Zr/
90
Zr = 0.3381 [Minster and
Alle`gre, 1982], Hf isotope values are normalized to
179
Hf/
177
Hf = 0.7325. Note that Blichert-Toft et al. [1997] and Sanloup et al. [2000]
report TIMS averages reproduced within error by MC-ICPMS. Zr isotope ratios obtained in Mu¨nster relative to
90
Zr/
91
Zr of 4.584
[Nomura et al., 1983] are
90
Zr/
91
Zr = 1.53110,
94
Zr/
91
Zr = 1.55528, and
96
Zr/
91
Zr = 0.25047.
Table 6. Important Interferences on Zr and Hf Isotope Measurements
a
Zr-Isotope Measurements Hf-Isotope Measurements
Isotope Interference Isotope Interference
90
Zr
50
Ti
40
Ar,
180
Hf
++ 56
Fe
35
Cl,
40
Ar
35
Cl
16
O,
173
Yb
157
Gd
16
O
91
Zr
182
W
++ 175
Lu
159
Tb
16
O
176
Yb,
176
Lu,
144
Nd
16
O
2
,
92
Zr
92
Mo,
52
Cr
40
Ar,
184
W
++ 176
Hf
160
Gd
16
O
93
Nb
53
Cr
40
Ar,
186
W
++ 177
Hf
161
Dy
16
O
94
Zr
94
Mo,
40
Ar
2
14
N
178
Hf
162
Dy
16
O
95
Mo
79
Br
16
O
179
Hf
163
Dy
16
O
96
Zr
96
Mo,
96
Ru,
40
Ar
2
16
O
180
Hf
180
W,
180
Ta
97
Mo
81
Br
16
O
a
Using the separation procedures as described and clean acids, these interferences are absent or typically less than 0.1% of the
interfered isotope (Mo on Zr, Figure 6).
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the collision cell gas flow rate. From 1999 to
2001, uncorrected
90
Zr/
91
Zr and
179
Hf/
177
Hf
ranged from 4.452 to 4.481 (2.3–2.9% mass
bias per amu) and from 0.7344 to 0.7475 (0.15–
1% mass bias per amu), respectively. Typical
drifts in mass bias were 500 ppm over one
measurement session. No dependence of expo-
nential law-normalized isotope ratios on chang-
ing mass bias was observed.
4.1. Zirconium Isotope Measurements
[23] Zirconium isotope ratios were normalized
to both
90
Zr/
91
Zr = 4.584 and
94
Zr/
90
Zr =
0.3378 [Nomura et al., 1983] using the expo-
nential law. The
90
Zr/
91
Zr value was confirmed
by our measurements of
90
Zr/
91
Zr normalized
to the
87
Sr/
88
Sr of NBS 987 (4.584 ± 4 (2s), 15
measurement sessions, Zr cup configuration 1,
Table 4). Normalizing Zr isotope ratios to both
90
Zr/
91
Zr and
94
Zr/
90
Zr ensures identification of
interferences on
94
Zr and
91
Zr. A normalization
solely to
94
Zr/
90
Zr, as previously used by TIMS
workers [Harper, 1996; Minster and Alle`gre,
1982; Sahoo and Masuda, 1997], might be
severely affected by (1) an inaccurate
94
Mo
interference correction and (2)
40
Ar
2
14
N
+
inter-
ferences generated in the plasma (Table 6).
Important potential interferences on
91
Zr
include
56
Fe
35
Cl
+
and
40
Ar
35
Cl
16
O
+
.Ironis
usually removed during our separation proce-
dure described above, and ArOCl interferences
In-run mass bias corrected Mo ratios
(MB+I mode)
Raw Mo ratios
0.0001 0.001 0.01 0.1 1
Mo/Zr
-10
-5
0
5
10
15
20
Zr
Offline mass bias corrected Mo ratios
0.0001 0.001 0.01 0.1 1
Mo/Zr
-10
-5
0
5
10
Zr
zircons
rutiles
basalts,meteorites
92
max Mo/Zr
for Zr, Zr
94
96
Zr (MB+I)
92
Zr (MB+I)
94
Zr (MB+I)
92
a)
b)
max.Mo/Zr
for Zr
96
ε
ε
maximum Mo/Zr
Figure 6. Zr isotope compositions obtained for AMES metal Zr solutions that were doped with variable
amounts of Mo. Results are reported in e-units relative to a Mo-free AMES Zr solution. (a) The most accurate
92
Mo interference correction is achieved by in-run correction of each measured ratio, where a mass bias
correction is also applied to the interference correction itself (see text). (b) An accurate Mo correction for
92
Zr
and
94
Zr is possible up to Mo/Zr of 1 10
2
, whereas for
96
Zr an accurate correction is only possible up to
Mo/Zr of 1 10
3
. These Mo/Zr ratios are far below typical values in basalts, meteorites, and Ti minerals
(0.01–1), thus requiring the separation of Mo from Zr by ion exchange chromatography as described in the
text.
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were negligible in most cases (ArCl levels at
mass 75 were monitored).
[24] Long-term values of
92
Zr/
91
Zr = 1.53110 ±
15 and
92
Zr/
90
Zr = 0.33324 ± 3 (2s, n = 20 aver-
ages of measurement sessions) were obtained
for AMES Zr. Typical external precisions for n
> 10 measurements during one measurement
session were ±0.6e (2s) for
92
Zr/
91
Zr and ±0.4e
(2s) for
94
Zr/
90
Zr. The external reproducibility
for samples was determined with 20 measure-
ments of the zircon NZ-159, which was pro-
cessed through chemistry. These measurements
gave values of 0.1 ± 0.7e (2s) for
92
Zr/
91
Zr
and 0.0 ± 0.5e (2s) for
94
Zr/
90
Zr relative to
AMES Zr, reflecting the true external reprodu-
cibility rather than just the daily within-run
reproducibility of the AMES solution.
[25] Molybdenum interferences on
92
Zr and
96
Zr were corrected using
95
Mo as an interfer-
ence monitor (Table 6) and the Mo abundances
of Lee and Halliday [1995]. Since
95
Mo and
97
Mo are both free of monatomic isobaric
interferences, it is possible to check for polya-
tomic peaks at mass 95 by monitoring
95
Mo/
97
Mo (1.66). The
79
Br
16
Oand
81
Br
16
O interferences may occur on masses
95 and 97 (Table 6) but in a ratio of 1. Oxide
rates and bromine levels (masses 79 and 81)
were therefore checked before each measure-
ment. The
96
Ruthenium interferences on
96
Zr
were corrected using
99
Ru as an interference
monitor and the Ru abundances of de Bie`vre
and Taylor [1993]. As determined by measure-
ments of Mo-doped Zr standards (Figure 6),
accurate
92
Zr measurements are possible at Mo/
Zr below 10
2
. Likewise, Mo/Zr below 1
10
3
and Ru/Zr below 1 10
2
are required
for accurate
96
Zr measurements.
4.2. Hf and Lu Measurements
[26] Measured Hf isotope values were cor-
rected for mass bias relative to
179
Hf/
177
Hf =
0.7325 [Patchett and Tatsumoto, 1980] using
the exponential law. A long-term
176
Hf/
177
Hf
value of 0.282151 ± 13 (2s, off-array base-
line, Table 5) was obtained for our AMES Hf,
which is isotopically indistinguishable from
the JMC-475 standard. The
176
Yb and
176
Lu
interferences on
176
Hf were corrected using
173
Yb and
175
Lu as interference monitors
(Table 4) and the isotope compositions of
Blichert-Toft et al. [1997] (Lu) and of Scherer
et al. [1999; unpublished data, 2001]
(
176
Yb/
173
Yb = 0.7939). Typically, no detect-
able amounts of sample rare earth elements
(REE) were observed in the Hf cuts. Isobaric
180
Ta and
180
W interferences on
180
Hf were
corrected using
181
Ta and
182
W as interference
monitors (Table 4) and the isotope composi-
tions of Lee and Halliday [1995] (W) and
Weyer et al. [2001] (
180
Ta/
181
Ta, 0.0001198 ±
6). The
176
Hf/
177
Hf and Lu/Hf for interna-
tional reference materials (Table 7) show good
agreement with literature data. Lu/Hf ratios
obtained for JB-1 and the Allende meteorite
agree with those reported by Patchett and
Tatsumoto [1980] and Blichert-Toft et al.
[1997] within ±1% (present 2s error), demon-
strating interlaboratory consistency of spike
calibrations. Lu-Hf concentrations were deter-
mined using a mixed
176
Lu-
180
Hf tracer that
has been calibrated against pure (99.9%)
AMES metal standards.
[27] Although previous MC-ICPMS proce-
dures for Lu measurement by isotope dilution
require a large correction for the isobaric
interference of
176
Yb on
176
Lu, a precision of
±1% has been achieved by normalization to
naturally occurring Yb in the Lu cut [Blichert-
Toft et al., 1997]. This precision is sufficient
for most applications, including calculation
of initial
176
Hf/
177
Hf for low-Lu/Hf samples.
In Mu¨nster, Lu ID measurements are made
using the method of Scherer et al. [1999],
where
176
Lu/
175
Lu is normalized to the
187
Re/
185
Re [de Bie`vre and Taylor, 1993] of
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admixed Re. For applications that require Lu/
Hf precisions better than 1%, the large Yb
interference correction is eliminated by pro-
cessing the sample through alpha-hydroxyiso-
butyric acid (aHIBA) chemistry [Gruau et
al., 1988] to remove Yb. This additional step
lowers the Lu/Hf uncertainties to ±0.2% (2s
external reproducibility [Scherer et al.,
2001]). The isotope compositions used for
the interference corrections of
176
Hf and
176
Yb on
176
Lu are
176
Hf/
177
Hf = 0.28216
[Blichert-Toft et al., 1997] and
176
Yb/
173
Yb =
0.7939 [Scherer et al., 1999; unpublished
data, 2001]. Like our
176
Lu/
175
Lu measure-
ments, this Yb isotope composition was cor-
rected for mass bias using admixed Re, thus
providing an internally consistent interference
correction.
5. Conclusions
[28] Our new HFSE separation procedures ena-
ble precise measurements of Nb/Ta and Zr/Hf
by isotope dilution, using a mixed
94
Zr-
176
Lu-
180
Hf-
180
Ta tracer. Lu-Hf separations
can be performed on a single column. This
procedure facilitates separation of Hf from
peridotites, garnets, and phosphates, opening
fundamentally new perspectives in Lu-Hf geo-
chronology. Using the Isoprobe MC-ICPMS, it
is possible to perform Hf isotope measurements
Table 7. The
176
Hf/
177
Hf and Lu/Hf Obtained for International Rock Reference Samples
a
Sample
176
Hf/
177
Hf eHf ppm Hf ppm Lu
176
Lu/
177
Hf Reference
JB-1 0.282946 ± 10 6.2 3.536 0.308 0.0124 this study
0.282966 ± 7 6.9 - - - this study
0.282941 ± 7 6.0 - - - this study
0.282904 ± 75 4.7 3.612 0.313 0.0123 Patchett and Tatsumoto [1980] average
0.282933 ± 44 5.7 3.559 0.303 0.0121 Patchett [1983b]
BCR-1 0.282892 ± 6 4.2 4.993 - - this study
0.282879 ± 8 3.8 - - - Blichert-Toft [2001]
BIR-1 0.283255 ± 9 17.1 0.572 0.244 0.0604 this study
0.283248 ± 8 16.8 - - - this study
0.283266 17.5 - - - Blichert-Toft [2001] average
BE-N 0.282939 ± 4 5.9 5.812 - - this study
0.282923 ± 9 5.3 5.808 0.246 0.00600 this study
0.282921 ± 6 5.3 - - - this study
0.282921 ± 5 5.3 - - - Blichert-Toft [2001]
AUG-7 0.283223 ± 11 15.9 2.511 0.340 0.0192 this study
0.283227 ± 6 16.1 - - - this study
0.283219 ± 12 15.8 - - - this study
0.283219 15.8 - - - Salters [1994] average
0.283200 15.1 - - - Blichert-Toft et al. [1997] average
KIL-19 0.283096 ± 7 11.5 4.514 0.279 0.00875 this study
0.283116 ± 4 12.2 - - - Blichert-Toft et al. [1999]
DR-N 0.282752 ± 7 -0.7 3.203 0.379 0.0168 this study
0.282761 ± 6 -0.4 - - - this study
0.282860 ± 6 3.1 - - - Blichert-Toft [2001]
Allende-MS 0.282855 ± 14 2.9 0.1970 0.0468 0.0337 this study
Allende (Cph) 0.282776 ± 15 0.1 0.2109 0.0498 0.0335 Blichert-Toft and Albare`de [1997]
Allende (SI) 0.282825 ± 11 1.9 0.1920 0.0461 0.0341 Blichert-Toft and Albare`de [1997]
a
All
176
Hf/
177
Hf data are reported relative to 0.282160 for JMC-475. Note that DR-N (zircon-rich) was digested by flux fusion (see
text), possibly explaining the deviation from the data of Blichert-Toft [2001] (acid digestion).
Geochemistry
Geophysics
Geosystems
G
3
G
3
mu¨ nker et al.: separation of high field strength elements 2001GC000183
on as little as 5 ng of Hf, thus permitting
176
Hf/
177
Hf measurements on small amounts
of low-abundance samples. Using a combined
anion resin and Ln-Spec procedure, it is possi-
ble to recover both a clean Zr cut and a quanti-
tative Zr-Nb cut from a single sample. Even
without a Nb tracer, a precision of ±5% (2s)is
achieved for Zr/Nb, thus enabling the routine
application of
92
Nb-
92
Zr chronometry to mete-
orite samples that contain as little as 10 ng Zr.
Acknowledgments
[29] This work was supported by grants Me 1717/1-1 and
ZG 3/16 of the Deutsche Forschungsgemeinschaft. Stefan
Weyer acknowledges support by the Max-Planck-Institut
fu¨r Chemie in Mainz. H.M. Baier is thanked for lab
support. M. Langer (Eichrom Paris) provided unpublished
information on Eichrom Ln-Spec resin. During the early
stages, this work benefited from fruitful discussions with
Mark Rehka¨mper. We thank J. Blichert-Toft and V. M.
Salters for helpful reviews.
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