Anal. Chem. 2002, 74, 67-73
Combined Chemical Separation of Lu, Hf, Sm, Nd,
and REEs from a Single Rock Digest: Precise and
Accurate Isotope Determinations of Lu-Hf and
Sm-Nd Using Multicollector-ICPMS
Ilka C. Kleinhanns,*,† Katharina Kreissig,‡ Balz S. Kamber,§ Thomas Meisel,| Thomas F. Na
1 gler,† and
Jan D. Kramers†
Gruppe Isotopengeologie, Mineralogisch-Petrographisches Institut, Universität Bern, Erlachstrasse 9a, CH-3012 Bern,
Switzerland, Department of Earth Sciences, University of Bristol, Queens Road, Bristol, BS8 1RJ, U.K., Department of Earth
Sciences, University of Queensland, Qld 4072 Brisbane, Australia, and Institut für allgemeine und analytische Chemie,
Universität Leoben, Franz-Josef-Strasse 18, A-8700 Leoben, Austria
A combined procedure for separating Lu, Hf, Sm, Nd, and
rare earth elements (REEs) from a single sample digest
is presented. The procedure consists of the following five
steps: (1) sample dissolution via sodium peroxide sintering; (2) separation of the high field strength elements
from the REEs and other matrix elements by a HF-free
anion-exchange column procedure; (3) purification of Hf
on a cation-exchange resin; (4) separation of REEs from
other matrix elements by cation exchange; (5) Lu, Sm,
and Nd separation from the other REEs by reversed-phase
ion chromatography. Analytical reproducibilities of
Sm-Nd and Lu-Hf isotope systematics are demonstrated
for standard solutions and international rock reference
materials. Results show overall good reproducibilities for
Sm-Nd systematics independent of the rock type analyzed. For the Lu-Hf systematics, the reproducibility of
the parent/daughter ratio is much better for JB-1 (basalt)
than for two analyzed felsic crustal rocks (DR-N and an
Archaean granitoid). It is demonstrated that this poorer
reproducibility of the Lu/Hf ratio is truly caused by
sample heterogeneity; thus, results are geologically reasonable.
The combination of Sm-Nd and Lu-Hf isotope systematics
with rare earth element (REE) patterns provides a powerful tool
for understanding Earth’s differentiation. Single mineral phases,
such as zircon and garnet, which play an important role in mantlecrust-related processes, reveal dissimilar behavior with respect
to the Sm-Nd and Lu-Hf systematics and to REE pattern. For
example, Hf is a major element in zircon with concentrations of
up to 3 wt %, whereas the concentration of Lu in this mineral phase
is 2 orders of magnitude lower, resulting in extremely low Lu/Hf
ratios. In contrast, both Sm and Nd are just trace elements in
* Corresponding author: (e-mail) ilka@mpi.unibe.ch; (fax) + 41 (0)31 631
49 88; (tel) +41 (0)31 631 85 33.
† Universität Bern.
‡ University of Bristol.
§ University of Queensland.
| Universität Leoben.
10.1021/ac010705z CCC: $22.00
Published on Web 11/20/2001
© 2002 American Chemical Society
zircon. Differing amounts of zircon in separate powder aliquots
of the same rock produce a strong variability in the measured
Lu/Hf ratios of the rock but do not significantly influence the Sm/
Nd ratios. Garnet, on the other hand, has very high partition
coefficients for heavy REEs, resulting in very high Lu/Hf and
moderately elevated Sm/Nd ratios. Hence, garnet influences the
overall budget and pattern of the REEs in rocks and effects the
Lu-Hf as well as the Sm-Nd isotope systematics. The same is
true for other mineral phases with high partition coefficients for
REE such as pyroxene, amphibole, or monazite. Total dissolution
of the rock powder aliquot is therefore essential if geological
interpretations are to be made by comparison of REE pattern with
Lu-Hf and Sm-Nd isotope systematics.
To develop a combined technique analyzing Sm-Nd and LuHf systematics as well as REEs (unspiked except for Nd, Sm, and
Lu), we adopted the method of sintering with sodium peroxide,
which is already in use for REE analyses on whole-rock samples.1
Sodium peroxide sintering is not only capable of dissolving even
very resistant mineral phases such as zircon, garnet, titanite, and
osmiridium2 but is also a very rapid digestion method. Further,
the method avoids the use of HF during sample digestion and
prior to separation of high field strength elements (HFSEs) and
REEs. This is favorable as problems in combined Sm-Nd and
Lu-Hf isotope as well as REE analyses may result from the
formation of fluorides3 or fluoride gels.4 These hinder complete
sample dissolution as well as complete spike-sample homogenization and risk strongly fractionating REEs. Indeed, problems with
spike-sample homogenization for the Lu-Hf isotope system were
mentioned,5,6 and low reproducibilities of the Lu/Hf ratio were
explained by fluoride precipitation.5 HFSE analyses problems
(1) Robinson, P.; Higgins, N. C.; Jenner, G. A. Chem. Geol. 1986, 55, 121137.
(2) Seelye, F. T.; Rafter, T. A. Nature 1950, 165, 317.
(3) Nägler, Th. F.; Kamber, B. S. Schweiz. Mineral. Petrogr. Mitt. 1996, 76,
75-80.
(4) Cohen, A. S.; O’Nions, R. K.; Siegenthaler, R.; Griffin, W. L. Contrib. Mineral.
Petrol. 1988, 98, 303-311.
(5) Blichert-Toft, J.; Albarède, F. Earth Planet. Sci. Lett. 1997, 148, 243-258.
(6) Scherer, E. E.; Cameron, K. L.; Johnson, C. M.; Beard, B. L.; Barovich, K.
M.; Collerson, K. D. Chem. Geol. 1997, 142, 63-78.
Analytical Chemistry, Vol. 74, No. 1, January 1, 2002 67
related to acid digestion were evaluated by Münker7 and Le Fèvre
and Pin.8
Variabilities in present-day isotope compositions of daughter
elements and parent/daughter ratios are well-known effects of
sample heterogeneity.6,9-13 However, if all mineral phases are in
isotopic equilibrium, the influence on initial daughter isotope ratios
by sample heterogeneity is zero. Heterogeneous distribution of
phases that are not in isotopic equilibrium, on the other hand,
can cause inconsistency between different isotope systems and
REEs when these geochemical tracers are determined on different
sample powder aliquots. This is due to different parent/daughter
ratios in different mineral phases of the sample and, hence,
different amounts of radiogenic ingrowth. To circumvent this
problem and allow direct comparison of REE pattern, Lu-Hf and
Sm-Nd isotope systematics of a single rock sample, the technique
presented here is based on chemical separation from a single
sample digest.
EXPERIMENTAL SECTION
Chemicals. Ultrapure water with a resistivity of 18.2 MΩ/cm
was used (Milli-Q). All acids were doubly distilled with the
exception of 12 M HCl, which has been cleaned using an anionexchange column. Pure sodium peroxide was purchased from
Fluka (Na2O2; purum g95%). Certified Johnson Matthey ICP
standard solutions (1000 ( 3 µg/mL; Hf solution Lot No.
5011537B; Lu solution Lot No. 601782M) were used to gravimetrically prepare standard solutions with known concentrations. These
solutions were used to calibrate the spike solution via multiple
MC-ICPMS measurements of spiked standard solutions.
Caution! HCl is toxic and corrosive even when diluted. HCl
gas is toxic and highly irritating the respiratory system. Handle
with great care!
Caution! HF is highly toxic and corrosive even when diluted.
It emits highly toxic HF gas. It irritates the skin and mucous
membranes of the body. Handle with great care!
Caution! Na2O2 is an oxidizing and corrosive substance. In
contact with combustible material, it may cause fire. Na2O2 is
strongly hygroscopic; keep container dry. Handle with great care!
Step 1: Sample Digestion. Finely ground sample powder
(100 mg) is weighed into glassy carbon vessels (Sigradur G)
together with 176Lu-180Hf mixed spike stabilized in 1 M H2SO4
and 149Sm-150Nd mixed spike stabilized in 1.6 M HCl. (The
stability of the Lu/Hf spike was tested over a three-month period.
The Lu/Hf spike ratio thereby remained stable within 0.4% (2 SD),
showing no indication of a variation with time). The suspension
is completely dried on a hot plate, and the powder is mechanically
desegregated with a spatula. Sodium peroxide is added as
sintering reagent. A sodium peroxide/sample ratio of 6:1 is
sufficient to ensure total decomposition of zircons in zircon-rich
rock powders. In zircon-poor or finer-grained materials, lower
(7) Münker, C. Chem. Geol. 1998, 144, 23-45.
(8) Le Fèvre, B.; Pin, C. Anal. Chem. 2001, 73, 2453-2460.
(9) Pettingill, H. S.; Patchett, P. J. Earth Planet. Sci. Lett. 1981, 55, 150-156.
(10) Na, C. N.; Nakano, T.; Tazawa, K.; Sakagawa, M.; Ito, T. Chem. Geol. 1995,
123, 225-237.
(11) Kane, J. S. Analyst 1997, 122, 1289-1292.
(12) Meisel, T.; Moser, J.; Wegschneider, W. Fresenius J. Anal. Chem. 2001,
370, 566-572.
(13) Scherer, E. E.; Cameron, K. L.; Blichert-Toft, J. Geochim. Cosmochim. Acta
2000, 64, 3413-3432.
68
Analytical Chemistry, Vol. 74, No. 1, January 1, 2002
sodium peroxide/sample ratios are adequate, and the procedural
blank is reduced. The spike-sample mixture and the sintering
reagent are carefully mixed with a spatula and finally covered with
a thin layer of sodium peroxide. Sintering is achieved by heating
in a muffle furnace at 480 ( 10 °C for 0.5 h.
After the sample is cooled to room temperature, water is
carefully added in small amounts, resulting in a vigorous exothermal reaction. Water is added until the reaction has fully
ceased. The result of this reaction is a suspension of precipitated
cation hydroxides in strong NaOH. The suspension is centrifuged
and the NaOH supernate, containing silica, is discarded. Addition
of water to the precipitate followed by centrifuging is repeated,
but this time the supernate liquid is transferred into a second vial.
HCl is added to the decanted liquid to test whether silica gel is
still evolving, which results in blurring the liquid. Water addition,
centrifugation, and HCl addition to the decanted supernate liquid
are repeated until no more silica gel forms (normally after one
repetition).
Step 2: Separation of HFSEs and REEs. The remaining
precipitates from the sample digestion are dissolved in 4 mL of
12 M HCl and loaded onto an anion-exchange column (3 mL of
Dowex AG1-X8, 200-400 mesh). Strong (>8 M) HCl is required
for loading the sample onto the column, because Ti, Zr, and Hf
do not adhere to anion-exchange resin in weaker HCl media. REEs
and other matrix elements are eluted into a vial for further REE
purification (step 4) using 19 mL of 12 M HCl. Ti is reduced in
the HFSE fraction and washed out with 2 mL of 6 M HCl. Finally,
the HSFEs are eluted together with Fe and Cr with 15 mL of 2.5
M HCl. Hf is separated from this cut in step 3.
Step 3: Purification of Hf. The HFSE solution from step 2
is dried to a small droplet and redissolved in 2 mL of 2.5 M HCl.
Addition of 100 µL of H2O2 to the sample solution forms yellow
chromium and iron peroxide complexes, which do not adhere to
cation-exchange resin. The solution is loaded onto a cationexchange column (4 mL of Dowex AG50W-X8, 200-400 mesh).
Ti, Cr, and Fe are eluted with 10 mL of 2.5 M HCl or until the
eluate is colorless. Purified Hf is eluted with 4 mL of 5 M HF and
dried. At this point, the sample is ready for mass spectrometry.
The use of HF in this step ensures high yields for Hf. There is no
risk of REE fractionation by fluoride precipitation, because the
REEs have already been separated from the HFSE during step 2.
Step 4: Purification of REEs. REE purification is performed
using a conventional cation-exchange column technique (3 mL
of Dowex AG50W-X8 resin, 200-400 mesh). The REE solution
from step 2 is evaporated, redissolved in 4 mL of 2.5 M HCl, and
loaded onto the column. Matrix elements are washed out with 11
mL of 2.5 M HCl, and the purified REE-fraction is eluted with 20
mL of 6 M HCl. Before further processing in step 5, a 0.5-mL
aliquot of the eluate is separated for determination of REE
concentrations for REE patterns.
Step 5: Separation of Nd, Sm, and Lu. Pure Nd, Sm, and
Lu fractions are obtained by reversed-phase chromatography
(modified after Richard14) (4 mL of HDEHP-coated Teflon in
quartz-glass columns). The REE solution from step 4 is evaporated,
redissolved in 300 µL of 0.18 M HCl, and loaded onto the column.
La, Ce, and Pr are washed out with 20 mL of 0.18 M HCl. Nd is
(14) Richard, P; Shimizu, N.; Allégre, C. J. Earth Planet. Sci. Lett. 1976, 31,
269-278.
collected in the next 6 mL of 0.18 M HCl. The remaining Nd is
fully washed out with 8 mL of 0.4 M HCl, which allows collection
of a Nd-free Sm fraction in the succeeding 7 mL 0.4 M HCl. A
Nd-free Sm fraction is favored to preclude any possible matrix
effect. Medium to heavy REEs, including Yb, are stripped off with
73 mL of 2.5 M HCl. Lu is collected in the following 15 mL of 2.5
M HCl. Complete separation of Yb and Lu is beneficial,15,16 as it
reduces corrections related to isobaric interference of 176Yb (13%
of natural Yb) on 176Lu (2.6% of natural Lu). Otherwise, these
corrections would be important, as Yb in geological samples is
general 4-7 times more abundant than Lu.
Mass Spectrometry. REE concentrations of unspiked solutions were measured on quadrupole ICPMS (HP4500, HewlettPackard) at the University of Leoben, following the procedures
of Meisel et al.17 Determination of Lu, Hf, Sm, and Nd isotope
ratios were carried out in static mode on Faraday collectors on
the Nu instruments multicollector ICPMS at the University of
Bern. Sample aspiration was performed using an Aridus desolvating nebulizer. Desolvating nebulizers have the advantage of
producing “dry” aerosols, which minimizes plasma fluctuations.
Apart from measuring all isotopes of a certain element simultaneously, the 12-Faraday collector array of the MC-ICPMS also
allows simultaneous monitoring of other elements with possible
interfering isotope masses. Isotopes monitored during Hf isotope
measurements were 173Yb (to correct for the 176Yb isobaric
interference on 176Hf), 175Lu (176Lu on 176Hf), 181Ta (180Ta on
180Hf), and 183W (180W on 180Hf). Monitored isotopes during Lu
isotope measurements were 178Hf (176Hf on 176Lu) and 174Yb
(176Yb on 176Lu), and during Nd isotopic measurements, 147Sm
(144Sm on 144Nd) and 140Ce (142Ce on 142Nd) were checked. During Sm isotope measurements (masses 147, 149, and 152), 156Gd
(152Gd on 152Sm) was monitored.
All uncertainties given in the following text are 2σ standard
deviations. Further, they comprise measurements with different
sample uptake systems (Aridus and Micromist with microcyclonic
spray chamber) over a long period of time. All Hf isotope ratios
are internally corrected for fractionation using a value of 0.7325
for 179Hf/177Hf and the exponential law. Measured values of
176Hf/177Hf, 178Hf/177Hf, and 180Hf/177Hf ratios of an in-house Hf
standard solution are 0.282 165 ( 12, 1.467 29 ( 8, and 1.8868 (
5, respectively for the period between November 1999 and
December 2000. Measured values of 176Hf/177Hf, 178Hf/177Hf, and
180Hf/177Hf ratios of the JMC 475 standard solution during the
same time period are 0.282 169 ( 16, 1.467 29 ( 8, and 1.8868 (
3, respectively. Remarkably, these two Hf standard solutions are
isotopically indistinguishable.
Assuming that instrumental mass bias follows the exponential
law, uncorrected 178Hf/177Hf and 176Hf/177Hf ratios should fit a
linear array in a ln(178Hf/177Hf) versus ln(176Hf/177Hf) plot. The
theoretical slope of this linear array can be calculated with eq 1:
slope )
ln(M176/M177)
(M178/M177)
) -1.0070
(1)
where M176, M177, and M178 are the exact atomic masses of 176Hf,
(15) Patchett, P. J.; Tatsumoto, M. Contrib. Mineral. Petrol. 1980, 75, 263-267.
(16) Gruau, G.; Cornichet, J.; Le Coz-Bouhnik, M. Chem. Geol. 1988, 72, 353356.
177Hf,
and 178Hf, respectively. Thus, the validity of exponential
fractionation can be tested by comparing the slope obtained from
uncorrected Hf ratios in the ln(178Hf/177Hf) versus ln(176Hf/177Hf)
plot with their respective calculated theoretical slope. Figure 1A
illustrates that within uncertainties the slopes obtained for
Hf in-house (i.e., -1.0085 ( 68) and JMC 475 (i.e. -1.0098 ( 68)
standard solutions are indistinguishable from each other and
equal to the calculated theoretical slope (see eq 1). As expected
from these observations, mass bias-corrected ratios of both
the Hf in-house standard solution and those of the JMC 475
standard solution plot within analytical uncertainty of the theoretical fractionation line (Figure 1B). Published mass biascorrected ln(178Hf/177Hf) and ln(176Hf/177Hf) ratios of the JMC 475
standard solution are also plotted in Figure 1B for comparison
with our results. Despite some variations in the 178Hf/177Hf values,
all laboratories report within uncertainties the same 176Hf/177Hf
ratio.
Lu has only two naturally occurring isotopes, which makes
internal mass bias correction impossible. The method of element
doping is applied to correct for mass bias, using W of known
isotope composition as a reference element. Tungsten is ideal as
doping agent for Lu measurements, since its range in isotope
masses is close to that of Lu, but it does not isobarically interfere.
The applicability of W doping for mass bias correction of the
175Lu/176Lu ratio was tested with the same approach that was used
for internal mass bias correction of Hf isotopes. We found a strong
linear correlation between uncorrected ln(175Lu/176Lu) and ln(182W/184W) ratios. Within uncertainty, the slope of the linear array
of 0.5358 ( 146 equals the theoretically calculated one of 0.5217,
indicating identical fractionation behavior of W and Lu. Relative
to a 182W/184W ratio of 0.864 98,18 our mass bias-corrected value
for 175Lu/176Lu is 37.72 ( 2. This value is 0.2% higher than the
one given by Scherer et al.19 (37.63 ( 2) using Re as doping agent
or Blichert-Toft et al.20 (37.65, no error cited) using Yb. However,
all quoted 175Lu/176Lu ratios are directly related to the applied
isotope composition of the respective doping agents. The problem
of unknown absolute Lu isotope composition is however demagnified for Lu isotope dilution analyses, if spike calibration and
sample measurement follow the same protocol. The relation of
the W ratio to the Lu ratio remained constant on the Nu
instruments multicollector ICPMS over the whole period (February to December 2000). Thus, no empirical corrections had to be
applied.
The measured 143Nd/144Nd and 145Nd/144Nd ratios of our inhouse Nd standard solution, between February and December
2000, were 0.511 066 ( 18 and 0.348 414 ( 26, respectively,
corresponding to a 143Nd/144Nd La Jolla value of 0.511 856. All
Nd isotope ratios were internally corrected for mass bias using a
value of 0.7219 for 146Nd/144Nd and the exponential law. Perfect
agreement between the theoretically calculated slope (see eq 1)
of -1.0048 and the slope defined by uncorrected Nd ratios of
-1.0024 ( 25 in the ln(143Nd/144Nd) versus ln(145Nd/144Nd) space
confirms the applicability of exponential mass bias correction.
(17) Meisel, T.; Schöner, N.; Paliulionyte, V.; Kahr, E. Geostand. Newsl., in press.
(18) Lee, D.-C.; Halliday, A. Nature 1995, 378, 771-774.
(19) Scherer, E. E.; Münker, C.; Rehkämper, M.; Mezger, K. Eos, Trans. 1999,
80, 1118.
(20) Blichert-Toft, J.; Chauvel, C.; Albarède, F. Contrib. Mineral. Petrol. 1997,
127, 248-260.
Analytical Chemistry, Vol. 74, No. 1, January 1, 2002
69
Figure 1. (A) Plot of ln(176Hf/177Hf) vs ln(178Hf/177Hf) showing strong
linear correlation for uncorrected ratios of the Hf in-house (filled
diamonds) and JMC 475 (crosses) standard solutions. (B) Detailed
view of the mass bias-corrected averages of the Hf in-house and JMC
475 standard (same symbols as in (A)). A comparison of our data
with that of other laboratories for the JMC 475 standard solution shows
that all laboratories measure similarly and are within uncertainty of
the theoretical fractionation line. The following symbols indicate the
Hf values presented in the references noted: 9,32 4,33 3,20 O,6 b,34
and ].13
RESULTS AND DISCUSSION
Yield and Blank Levels. For Hf, a yield of 90% was obtained,
which is comparable to published recoveries.6,15,20 Recoveries of
Sm and Nd are deliberately held around 90% and for Lu around
60%. The loss occurs during REE separation (step 5), since high
levels of Ce in Nd, Nd in Sm, and Yb in Lu fractions have to be
avoided to minimize isobaric interferences as well as possible
matrix effects during measurements. The low recovery for Lu is
comparable to that of Patchett and Tatsumoto21 with 50% and that
of Gruau et al.16 with 65%, who also aimed for low Yb levels in the
Lu fraction. However, with complete spike-sample homogenization, the somewhat lower Lu yield does not affect the accuracy of
Lu concentration determinations or Lu/Hf ratios.
The chemistry blank for Nd is below 20 pg, suggesting
negligible overall REE blanks. For Hf, a chemistry blank of 90 pg
was determined. The total procedural blanks for Nd and Hf,
including sample digestion, are 370 and 330 pg, respectively,
corresponding to a blank contribution of Hf and Nd to the sample
(21) Patchett, P. J.; Tatsumoto, M., Geophys. Res. Lett. 1980, 7, 1077-1080.
70
Analytical Chemistry, Vol. 74, No. 1, January 1, 2002
analyte of below 0.1%, respectively. The main blank contribution
can be related to the flux reagent sodium peroxide, which cannot
be especially cleaned. However, as Scherer et al.6 pointed out,
the effect of the blank on the measured Hf ratios is negligible as
long as the blank contribution to the sample Hf is below 0.24%.
Reproducibility of Natural Rock Samples. Two international
rock reference materials (basaltic JB-1 and dioritic DR-N) were
measured for Sm-Nd and Lu-Hf systematics on a MC-ICPMS
(using isotope dilution for concentration determinations), as well
as for REE concentrations on a quadrupole ICPMS (using external
calibration for concentration determinations) to check the reliability of the developed technique for different rock types.
Additionally, a sample from the Archaean Dalmein pluton, Barberton Mountain Land (South Africa) was analyzed to quantify
the accuracy and reproducibility of age-corrected Nd and Hf
isotope ratios and Nd and Hf mantle extraction model ages. The
Dalmein pluton is a medium-grained biotite-granodiorite with a
well-constrained age of 3216+2/-1 Ma (U/Pb-zircon22). Several
100-mg aliquots of JB-1 and DR-N were digested with sodium
peroxide sintering. Separation of Lu, Hf, Sm, Nd, and REEs on
all sample solutions was carried out with the chemical separation
procedure described above. For comparison, 100-mg powder
aliquots of both reference materials were digested with conventional acid attack for Sm-Nd systematic and REE. All REE
measurements are given in Table 1 and Lu-Hf and Sm-Nd
isotope results in Table 2.
Independent of the digestion method used, Sm/Nd as well as
Nd/Lu ratios of JB-1 determined by isotope dilution were
consistent. The same holds true for DR-N. In addition, the obtained
values of both rock reference materials agree well with those
reported in the literature (Table 1). Quadrupole ICPMS results
of Sm/Nd and Nd/Lu ratios of sintered powder aliquots are equal
to those obtained by isotope dilution on MC-ICPMS and thus to
literature values. Interestingly, Sm/Nd and Nd/Lu ratios determined by external calibration on quadrupole ICPMS from samples
digested by acid attack are slightly different (Table 1). However,
Eu anomalies (eq 2; N denotes chondrite-normalization) are
Eu/Eu* )
EuN
x(SmN × GdN)
(2)
identical and correspond to literature values (Table 1), independent of the digestion method and measuring technique used.
It would be rather speculative to explain why acid-digested
aliquots reveal a slight discrepancy from literature values in Sm/
Nd and Nd/Lu ratios when determined by external calibration;
however, this is not the aim of the study. The major observation
concerning the reliability of our chemical separation procedure
and that of the sodium peroxide sintering is the excellent
reproducibility of the Sm/Nd and Nd/Lu ratios, independent of
the measuring technique.
The 147Sm/144Nd and 143Nd/144Nd ratios reproduce well regardless of the rock type analyzed and the digestion technique used
(Table 2). Mean Nd mantle extraction ages of JB-1 and DR-N are
consistent for both digestion techniques, respectively. Additionally,
Sm and Nd concentrations of DR-N using the sintering digestion
(22) Kamo, S. L.; Davis, D. W. Tectonics 1994, 13, 167-192.
Table 1. Comparison of the Elemental Ratios Sm/Nd,
Nd/Lu, and Eu/Eu*a for Reference Materials JB-1 and
DR-Nb
sinter 1
sinter 2
HF-HNO3 1
HF-HNO3 2
JB-1
ID-MC-ICPMS
Quad. ICPMS
ID-MC-ICPMS
Quad. ICPMS
ID-MC-ICPMS
Quad. ICPMS
ID-MC-ICPMS
Quad. ICPMS
XRF
INAA
ID-MS
sinter 1
sinter 3
HF-HNO3 1
HF-HNO3 2
ICP-AES
ICPMS
HPLC-ID-MS
DR-N
ID-MC-ICPMS
Quad. ICPMS
ID-MC-ICPMS
Quad. ICPMS
ID-MC-ICPMS
Quad. ICPMS
ID-MC-ICPMS
Quad. ICPMS
Sm/Nd
Nd/Lu
0.192
0.192
0.193
0.197
0.194
0.202
0.193
0.201
0.196
0.188
0.189
81.2
85.3
77.1
82.1
0.223
0.228
0.223
0.226
0.224
0.236
0.224
0.236
0.228
0.224
0.211
Eu/Eu*
0.93
0.94
87.5
0.93
86.7
109.2
82.1
87.1
0.94
0.89
0.96
0.95
63.2
62.5
62.9
62.0
0.86
0.85
61.6
0.86
60.5
60.3
66.2
56.1
0.86
0.85
0.88
0.89
a See text for calculation. b ID-MC-ICPMS, this work, isotope dilution
multicollector ICP-mass spectrometry, Bern; Quad. ICPMS, this work,
external calibration, quadrupole ICP-mass spectrometry, Leoben; XRF,1
X-ray fluorescence spectrometry, sinter digestion; INAA, see references
in ref 1, instrumental neutron activation analysis; ID-MS, see references
in ref 1, isotope dilution mass spectrometry; ICP-AES,27 ICP-atomic
emission spectrometry; ICPMS,25 ICP-mass spectrometry; HPLC-IDMS,28 high-performance liquid chromatography-isotope dilution-mass
spectrometry.
are 5.25 and 23.6 µg/g, respectively, values that are identical to
those of 5.22 µg/g Sm and 23.3 µg/g Nd reported by Pin and
Zalduegi.23 However, these authors reported 143Nd/144Nd ratios
of 0.512 425 ( 7 and 0.512 428 ( 8 for DR-N (Table 2), values
that are somewhat higher than ours. Comparison with their SmNd systematics via mantle extraction ages, on the other hand,
reveals ages identical to our results (Table 2). The five sintered
aliquots of the Dalmein pluton yield the highest uncertainty level
for Sm-Nd systematics ((0.5 units for the 143Nd/144Nd ratio
and 1.4% for the 147Sm/144Nd ratio); however, they exhibit wellconstrained mantle extraction ages (mean age, 3.35 ( 0.02 Ga).
The reproducibility for age-corrected 143Nd/144Nd ratios of the
Dalmein pluton is much better than that for its present-day
143Nd/144Nd ratios, which indicates a correlated variation of Nd
isotope and Sm/Nd ratios that is due to sample heterogeneity.
Reproducibility of Lu-Hf whole-rock data is strongly dependent on total sample decomposition as mentioned above. The ability
of sodium peroxide sintering to dissolve zircon was tested using
a “synthetic sample” composed of 80 mg of chalcedony powder
and 20 mg of zircon crystals (30-60-µm grain size). The full
decomposition of zircon crystals was verified by dissolving the
remaining precipitates after centrifugation (step 1) in 12 M HCl
and checking for undissolved matter under a binocular microscope. No detectable grains or gels remained even though the
surface/mass ratio in the “synthetic sample” was smaller than in
whole-rock powders.
(23) Pin, C.; Zalduegi, J. F. S. Anal. Chim. Acta 1997, 339, 79-89.
Mean values obtained for three powder aliquots of JB-1 are
) 0.0147 ( 0.8% and 176Hf/177Hf ) 0.282 974 ( 11. Our
elemental Lu/Hf ratios are close to the average of published values
that were determined with different analytical techniques (Figure
2) but higher than those determined by Patchett and Tatsumoto21
and Patchett.24 The latter difference is, however, positively
correlated with variations in the Hf isotope composition determined during this study and in Patchett and Tatsumoto21 and
Patchett,24 thus indicating sample heterogeneity. Indeed, sample
heterogeneity in different batches of JB-1, caused by irregular
distribution of Hf- or Lu-bearing phases, would perfectly account
for the correlated variations observed, as revealed by the respective mantle extraction ages of JB-1 in both studies: These are
identical within uncertainties (mean age, 0.62 ( 0.02 Ga and 0.64
( 0.12 Ga, respectively).
Compared to JB-1, the dioritic reference material DR-N shows
poorer reproducibilities for 176Lu/177Hf and 176Hf/177Hf ratios of
4.1% and (2 units, respectively. However, determined concentrations for Lu and Hf agree well with reported literature values (e.g.,
Garbe-Schönberg:25 Lu, 0.34 µg/g; Hf, 3.56 µg/g). Since DR-N is
coarser grained than JB-1 and it is rich in zircons, poorer
reproducibilities for its Lu-Hf analytical data were expected due
to greater sample heterogeneity. A recently published26 value for
the Hf isotope composition of DR-N of 0.282 860 ( 6 (2 SE) is
higher than those reported in this study. Unfortunately, the author
did not report the Lu/Hf ratio, and therefore, heterogeneity within
the different batches cannot be accessed via Hf isotope composition versus Lu/Hf correlations. To further evaluate the influence
and dependence of sample heterogeneity with respect to Lu-Hf
systematics, five powder aliquots from the Archaean Dalmein
pluton were also analyzed. The effect of sample heterogeneity
should increase with the age of the sample due to variable
radiogenic ingrowth in different phases. The reproducibility of the
176Lu/177Hf ratio of the Dalmein pluton is (4.0%, which is similar
to that of DR-N ((4.1%). The measured present-day 176Hf/177Hf
ratios, on the other hand, are well reproducible. If poorer
reproducibilities in 176Lu/177Hf ratios for felsic crustal rocks are
truly caused by sample heterogeneity, reproducibility of agecorrected 176Hf/177Hf ratios should stay at the same level or
diminish, compared to that of present-day 176Hf/177Hf ratios.
Indeed, mantle extraction ages (3.34 ( 0.06 Ga) and age-corrected
176Hf/177Hf (0.280 694 ( 34) are highly reproducible (Table 2).
Effect of Zircon on Sm-Nd and Lu-Hf Systematics.
Re-Os is another isotope system that is highly sensitive to
heterogeneous phase distribution in sample powders.12 The
influence on Re-Os systematics by irregular distribution of
osmiridium in powder aliquots of the same rock sample, the so176Lu/177Hf
(24) Patchett, P. J. Lithos 1983, 16, 47-51.
(25) Garbe-Schönberg, C.-D. Geostand. Newsl. 1993, 17, 81-97.
(26) Blichert-Toft, J. Geostand. Newsl. 2001, 25, 41-56.
(27) Watkins, J. P.; Nolan, J. Geostand. Newsl. 1990, 14, 11-20.
(28) Verma, S. P. Geostand. Newsl. 1991, 15, 129-134.
(29) Nägler, Th. F.; Kramers, J. D. Precambrian Res. 1998, 91, 233-252.
(30) Nir-el, Y.; Lavi, N. Appl. Radiat. Isot. 1998, 49, 1653-1655.
(31) Kramers J. D.; Kleinhanns, I. C.; Kreissig, K., Naegler, Th. F. EUG 11 Abst.
Vol. 2001, p 421.
(32) Patchett, P. J. Geochim. Cosmochim. Acta 1983, 47, 81-91.
(33) Stevenson, R. K.; Patchett, P. J. Geochim. Cosmochim. Acta 1990, 54, 16831697.
(34) Amelin, Y.; Lee, D.-C.; Halliday, A. N. Geochim. Cosmochim. Acta 2000,
64, 4205-4225.
Analytical Chemistry, Vol. 74, No. 1, January 1, 2002
71
Table 2. Sm-Nd and Lu-Hf Data for JB-1, DR-N, and the Dalmein Plutona
Sm
(ppm)
Nd
(ppm)
147Sm/
143Nd/
144Nd
144Nd
TDM(Nd)b
(Ga)
sinter 1
sinter 2
sinter 3
5.25
5.34
5.20
27.32
27.69
27.09
0.1162
0.1166
0.1161
0.512754 ( 07
0.512731 ( 08
0.512742 ( 07
0.61
0.64
0.62
average
2 SD
5.27
0.14
27.37
0.61
0.1163
0.0005
0.512743
0.000023
0.62
0.04
HF-HNO3 1
HF-HNO3 2
HF-HNO3 3
5.19
5.22
5.15
26.85
27.04
26.82
0.1170
0.1168
0.1161
0.512744 ( 06
0.512754 ( 06
0.512743 ( 06
0.63
0.61
0.62
average
2 SD
5.19
0.07
26.90
0.24
0.1166
0.0009
0.512747
0.000013
0.62
0.02
Hf
(ppm)
176Lu/
176Hf/
177Hf
177Hf
TDM(Hf)c
(Ga)
0.337
0.359
0.331
3.25
3.44
3.20
0.0147
0.0147
0.0146
0.282980 ( 07
0.282970 ( 07
0.282972 ( 07
0.61
0.63
0.63
0.34
0.03
3.30
0.26
0.0147
0.0001
0.282974
0.000011
0.62
0.02
0.303
0.313
0.303
3.56
3.61
3.76
0.0121
0.0123
0.0114
0.282956 ( 47
0.282895 ( 63
0.282939 ( 89
0.60
0.71
0.62
Lu
(ppm)
143Nd/
144Nd
(t)d
176Hf/
177Hf
(t)d
JB-1
HF-HCl24
HF-HNO321
HF-HNO321
sinter 1
sinter 2
sinter 3
sinter 4
5.26
5.25
5.23
5.27
23.63
23.48
23.46
23.70
0.1346
0.1352
0.1346
0.1344
0.512405 ( 08
0.512404 ( 08
0.512407 ( 06
0.512407 ( 07
1.33
1.34
1.33
1.33
DR-N
0.374
0.378
0.373
0.376
3.43
3.57
3.46
3.61
0.0154
0.0150
0.0153
0.0147
0.282752 ( 11
0.282809 ( 12
0.282743 ( 11
0.282755 ( 12
1.09
0.96
1.11
1.06
average
2 SD
5.25
0.04
23.57
0.23
0.1347
0.0007
0.512406
0.000003
1.33
0.02
0.375
0.004
3.52
0.17
0.0151
0.0006
0.282765
0.000060
1.06
0.13
HF-HNO3 1
HF-HNO3 2
HF-HNO3 3
5.24
5.26
5.26
23.42
23.50
23.54
0.1353
0.1352
0.1351
0.512406 ( 08
0.512403 ( 07
0.512412 ( 06
1.34
1.35
1.33
average
2 SD
5.25
0.02
23.49
0.12
0.1352
0.0002
0.512407
0.000009
1.34
0.02
HClO4-HF-HNO323
HClO4-HF-HNO323
5.22
5.22
23.3
23.3
0.1355
0.1356
0.512425 ( 07
0.512428 ( 08
1.31
1.31
sinter 1
sinter 2
sinter 3
sinter 4
sinter 5
8.26
8.73
7.96
8.74
8.51
52.44
54.06
49.34
54.56
53.48
0.0964
0.0976
0.0975
0.0968
0.0961
0.510460 ( 10
0.510483 ( 08
0.510482 ( 09
0.510481 ( 07
0.510464 ( 08
Dalmein Pluton
3.35
0.230
3.36
0.244
3.35
0.223
3.33
0.246
3.34
0.232
4.35
4.73
4.39
4.66
4.35
0.0075
0.0073
0.0072
0.0075
0.0075
0.281163 ( 09
0.281133 ( 09
0.281163 ( 13
0.281138 ( 13
0.281150 ( 10
3.32
3.35
3.29
3.36
3.35
0.508412
0.508409
0.508410
0.508423
0.508420
0.280702
0.280683
0.280720
0.280679
0.280685
average
2 SD
8.46
0.64
52.78
4.15
0.0969
0.0013
0.510474
0.000022
4.49
0.37
0.0074
0.0003
0.281149
0.000027
3.34
0.06
0.508415
0.000013
0.280694
0.000034
3.35
0.02
0.235
0.020
a In-run precisions given as 2 standard errors in the last decimal places; 143Nd/144Nd 0.511066 ( 18 corresponding to La Jolla 143Nd values of
Pin and Zalduegi;23 JMC 475 176Hf/177Hf of 0.282169 ( 16 during this study; quoted values of Patchett and Tatsumoto.21 b Calculated after Nägler
and Kramers.29 c Calculated with the 176Lu decay constant30 of 1.858 × 10-11 yr-1 and after Kramers et al.31 d Calculated using the zircon age of
Kamo and Davis.22
Figure 2. Reproduced Lu/Hf ratios of JB-1 obtained by sodium
peroxide sintering and MC-ICPMS measurements (triangles) compared to published Lu/Hf ratios: TIMS, 9,21,24 (recalculated from
original isotope ratios); INAA, (; SIMS, 2; ICPSM, b. SIMS, and
ICPMS data compiled by the Geological Survey of Japan (available
on www.aist.go/GSJ)). Data points displaying ∼60% scatter (excluding
three most extreme values ∼30%) indicating sample heterogeneity
within different batches of JB-1.
called “nugget effect”, is similar to the effect zircon has on the
Lu-Hf systematics. Poor reproducibilities for Zr concentrations
of zircon-bearing samples are explained by sample heterogeneity
with respect to the distribution of zircon throughout the whole72
Analytical Chemistry, Vol. 74, No. 1, January 1, 2002
rock powder.11 Since Hf and Zr display similar geochemical
behavior, poor reproducibilities of the 176Lu/177Hf ratios in felsic
crustal rocks are no surprise. Zircon, an accessory phase in felsic
crustal rocks, displays Hf concentrations 4 orders of magnitude
higher than whole rock, whereas the concentration difference for
Lu is only 2 orders of magnitude. In conclusion, reproducibility
of the 176Lu/177Hf ratio depends mainly on the distribution of Luand Hf-bearing phases throughout powdered whole-rock samples.
However, 147Sm/144Nd ratios are much less affected by heterogeneous phase distribution. Sm/Nd ratios are more evenly distributed throughout different mineral phases, and differences in the
order of that described for zircon with respect to the Lu-Hf
system do not occur. Model calculations reveal that a 4% variation
in the Lu/Hf ratio of felsic crustal rocks, as obtained for aliquots
of DR-N and Dalmein pluton, can be caused by only 1.5 µg of
additional zircon relative to an aliquot size of 100 mg.
CONCLUSIONS
Using a time-efficient analytical approach to combined
Lu-Hf, Sm-Nd, and REE determinations, as presented here,
demagnifies problems related to sample heterogeneity. The latter
was found to be important even in homogenized international rock
reference materials.
The principal cause of sample heterogeneity can be traced to
irregular distribution of mineral phases, with large concentration
differences relative to whole rock of one of the respective
elements. In particular, zircon strongly affects the Lu-Hf systematics of powder aliquots, whereas its effect on Sm-Nd
systematics is much smaller.
The perfect reproducibility in age-corrected 176Hf/177Hf ratios
and Hf mantle extraction ages of the powdered reference rock
materials is the strongest evidence that the observed variability
of (4% for the 176Lu/177Hf ratio in felsic crustal rocks is due to
the above-mentioned feature. This variability therefore ultimately
limits the reproducibility of Lu/Hf ratios.
As this type of heterogeneity is significantly more important
in different batches of the same geological material, comparison
of separated Lu-Hf, Sm-Nd, and REE determinations should be
avoided. Direct comparison of Lu-Hf systematics with Sm-Nd
systematics and REE pattern therefore requires separation and
determination of these geochemical tracers to be done on a single
rock powder aliquot.
ACKNOWLEDGMENT
This study was supported by the Swiss National Science
Foundation, Grant 20-61933-00. Ronny Schoenberg, Barbara Seth,
and Igor Villa are thanked for fruitful discussions and constructive
criticism on an earlier version of the manuscript. Two anonymous
reviewers are thanked for thoughtful comments.
Received for review June 25, 2001. Accepted September
19, 2001.
AC010705Z
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73