A practical guide for the design and implementation of the double-spike technique for precise determination of molybdenum isotope compositions of environmental samples (original) (raw)
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Geochemistry, Geophysics, Geosystems, 2001
1] Abstract: Molybdenum isotopic compositions are precisely determined by MC-ICP-MS measurements using a Mo double spike. The double spike is added prior to chemical purification, so that laboratory and instrumental mass fractionations are separated from natural mass-dependent fractionation. Fractionation is determined on four Mo mass ratios, providing an internal consistency check. The external standard reproducibility is at 0.06 per mil on the 98 Mo/ 95 Mo ratio (2 standard deviation)). Using a normal microconcentric nebuliser with a cyclonic spray chamber, the minimum quantity of Mo is $1 mg for high-precision results. A hydrothermal molybdenite shows fractionation of À0.3 per mil on the 98 Mo/ 95 Mo ratio relative to our standard (Johnson Matthey, 1000 mg/mL (0.3%) ICP standard solution, lot 602332B). Fine-grained sediments show fractionation of 0.1 and À0.3 per mil on the 98 Mo/ 95 Mo ratio. The observed Mo isotope fractionation is small but resolvable with the presented high-resolution technique. , 2001. Determination of molybdenum isotope fractionation by doublespike multicollector inductively coupled plasma mass spectrometry,
Determination of Molybdenum Isotope Fractionation by Double Spike MC-ICP-MS
1] Abstract: Molybdenum isotopic compositions are precisely determined by MC-ICP-MS measurements using a Mo double spike. The double spike is added prior to chemical purification, so that laboratory and instrumental mass fractionations are separated from natural mass-dependent fractionation. Fractionation is determined on four Mo mass ratios, providing an internal consistency check. The external standard reproducibility is at 0.06 per mil on the 98 Mo/ 95 Mo ratio (2 standard deviation)). Using a normal microconcentric nebuliser with a cyclonic spray chamber, the minimum quantity of Mo is $1 mg for high-precision results. A hydrothermal molybdenite shows fractionation of À0.3 per mil on the 98 Mo/ 95 Mo ratio relative to our standard (Johnson Matthey, 1000 mg/mL (0.3%) ICP standard solution, lot 602332B). Fine-grained sediments show fractionation of 0.1 and À0.3 per mil on the 98 Mo/ 95 Mo ratio. The observed Mo isotope fractionation is small but resolvable with the presented high-resolution technique. , 2001. Determination of molybdenum isotope fractionation by doublespike multicollector inductively coupled plasma mass spectrometry,
Molybdenum isotope ratio measurements on geological samples by MC-ICPMS
International Journal of Mass Spectrometry, 2005
A method using multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS) for the precise measurement of Mo isotopic composition in geological samples has been developed. Purification of Mo for isotope ratio measurements was realized by ionexchange chromatography using the chelating resin Chelex-100. This technique allows an efficient separation of Mo from an excess of Fe in samples and at the same time provides quantitative recovery of Mo. Instrumental mass discrimination is corrected by using Pd spiking and normalization to the 105 Pd/ 104 Pd ratio. Mo isotope ratios of samples are expressed in per mil relative to those of the bracketing in-house Mo standard. The long-term reproducibility at the two standard deviation level is 0.04, 0.06, 0.08 and 0.14‰ for 96 Mo/ 95 Mo, 97 Mo/ 95 Mo, 98 Mo/ 95 Mo and 100 Mo/ 95 Mo ratio measurements, respectively. The technique has been applied to measurement of the Mo isotopic composition of freshwater sediments and molybdenites. Mass-dependent variations in the isotopic composition of Mo spanning the range of ∼2.2‰ in terms of the 97 Mo/ 95 Mo ratio for two sediment columns from different redox environments have been resolved. These results show that Mo isotope effects induced by geochemical processes operating during weathering and transport of Mo to the oceans should be quantified in order to interpret global Mo isotope budget and make use of stable Mo isotopes as proxy for redox conditions in the geological past.
Geostandards and Geoanalytical Research, 2014
A novel preconcentration method is presented for the determination of Mo isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) in geological samples. The method is based on the separation of Mo by extraction chromatography using N-benzoyl-N-phenylhydroxylamine (BPHA) supported on a microporous acrylic ester polymeric resin (Amberlite CG-71). By optimising the procedure, Mo could be simply and effectively separated from virtually all matrix elements with a single pass through a small volume of BPHA resin (0.5 ml). This technique for separation and enrichment of Mo is characterised by high selectivity, column efficiency and recovery (~100%), and low total procedural blank (~0.18 ng). A 100 Mo-97 Mo double spike was mixed with samples before digestion and column separation, which enabled natural mass-dependent isotopic fractionation to be determined with a measurement reproducibility of < 0.09‰ (d 98/95 Mo, 2s) by MC-ICP-MS. The mean d 98/95 Mo SRM 3134 (NIST SRM 3134 Mo reference material; Lot No. 891307) composition of the IAPSO seawater reference material measured in this study was 2.00 ± 0.03‰ (2s, n = 3), which is consistent with previously published values. The described procedure facilitated efficient and rapid Mo isotopic determination in various types of geological samples. Une nouvelle m ethode de pr e-concentration est pr esent ee pour la d etermination des rapports isotopiques du Mo par spectrom etrie de masse a source plasma et multi-collection (MC -ICP-MS) dans des echantillons g eologiques. La m ethode est bas ee sur la s eparation du Mo par Chromatographie d'extraction en utilisant du Nbenzoyle-N-ph enylhydroxylamine (BPHA) support e par une r esine polym ere d'ester acrylique microporeuse (Amberlite CG-71). En optimisant la proc edure, le Mo peutêtre simplement et efficacement s epar e de la quasitotalit e des el ements de la matrice avec un seul passage a travers un petit volume de r esine BPHA (0,5 ml). Cette technique de s eparation et d'enrichissement du Mo est caract eris ee par une grande s electivit e, une grande efficacit e et une grande r ecup eration de la colonne (~100%), et un faible total de la proc edure de blanc (~0,18 ng). Un double spike Mo 100 -Mo 97 a et e m elang e avec les echantillons avant la digestion et la s eparation sur colonne, ce qui a permis la d etermination du fractionnement isotopique naturel d ependant de la masse avec une reproductibilit e de mesure de < 0,09 ‰ ( d98/95 Mo, 2s) par MC -ICP-MS. La composition moyenne d 98/95 Mo SRM3134 (mat eriau de r ef erence NIST SRM 3134 Mo; Lot n°891307) de l'eau de mer de r ef erence IAPSO mesur ee dans cette etude est de 2,00 ± 0,03 ‰ (2s, n = 3), ce qui est coh erent avec les valeurs pr ec edemment publi ees. La proc edure d ecrite facilite une d etermination efficace et rapide des rapports isotopiques du Mo dans divers types d' echantillons g eologiques.
Resolution of inter-laboratory discrepancies in Mo isotope data: an intercalibration
Journal of Analytical Atomic Spectrometry, 2013
The molybdenum (Mo) stable isotope system has been applied to a variety of geochemical and environmental problems. In the absence of a universally accepted zero-delta reference material, different groups report their data relative to their adopted in-house standards. Rigorous comparison of results generated in different laboratories using different analytical approaches is only possible if the inhouse standards are of identical Mo isotope composition. To determine potential isotopic differences among various standards, the d 98 Mo ( 98 Mo/ 95 Mo) values of ten Mo standard solutions were measured as part of this study. For six of these solutions, four laboratories carried out an intercalibration. In contrast to previous results, d 98 Mo of various in-house standards were found to differ by up to 0.37&. Renormalisation of our new and published Mo-isotope data available for seawater taken from various sites and the USGS rock reference material SDO-1 relative to NIST-SRM-3134, provides a much better agreement among reported d 98 Mo values for these samples. Relative to NIST-SRM-3134, the d 98 Mo of SDO-1 is 0.80 AE 0.14& (2s), while oxic, open-ocean seawater is characterised by an average d 98 Mo of 2.09 AE 0.10& (2s). This intercalibration provides a solid platform for comparing and amending existing d 98 Mo values. In addition, we recommend that future Mo isotope studies adopt NIST-SRM-3134 as a universal zero-delta reference material.
Proposal for an International Molybdenum Isotope Measurement Standard and Data Representation
Geostandards and Geoanalytical Research, 2013
Molybdenum isotopes are increasingly widely applied in Earth Sciences. They are primarily used to investigate the oxygenation of Earth's ocean and atmosphere. However, more and more fields of application are being developed; e.g. magmatic and hydrothermal processes, planetary sciences or the tracking of environmental pollution. Here we present a proposal for a unifying presentation of Mo isotope ratios in studies of mass dependent isotope fractionation. We suggest that the δ 98/95 Mo of the NIST SRM3134 be defined as +0.25‰. The rationale is that the vast majority of published data are presented relative to reference materials that are similar, but not identical, and
Molybdenum isotope records as a potential new proxy for paleoceanography
New high-precision isotope ratios of dissolved Mo in seawater from different ocean basins and depths show a homogeneous isotope composition ('mean ocean water 98 Mo/ 95 Mo' (MOMO)), as expected from its long ocean residence time (800 kyr). This composition appears to have been constant for the past 60 Myr at a 1^3 Myr time resolution as indicated from thick sections of Fe^Mn crusts from the Atlantic and Pacific. These records yield a constant offset from MOMO (average of 33.1 and 32.9x). They are similar to our new data on recent oxic Mo sinks: pelagic sediments and six Fe^Mn crust surface layers range from 32.7 to 32.9x and 32.7 to 33.1x, respectively. Recent suboxic Mo sinks from open ocean basins display heavier and more variable isotope ratios (30.7 to 31.6x relative to MOMO). Crustal Mo sources were characterized by measuring two granites (and a mild acid leach of one granite), seven volcanic rocks and two clastic sediments. All show a narrow range of compositions (32.0 to 32.3x). These data indicate that isotope fractionation by chemical weathering and magmatic processes is insignificant on a global scale. They therefore represent good estimates of the composition of dissolved Mo input to the oceans and that of the average continental crust. Thus, the Mo input into the oceans appears to be distributed into lighter oxic sinks and heavier reducing sinks. This is consistent with steady-state conditions in the modern ocean. The constant isotope offset between oxic sediments and seawater suggests that the relative amounts of oxic and reducing Mo removal fluxes have not varied by more than 10% over the last 60 Myr. An equilibrium fractionation process is proposed assuming that Mo isotope fractionation occurs between (dominant) MoO 23 4 and (minor) Mo(OH) 6 species in solution, of which the latter is preferentially scavenged. ß
A novel preconcentration method is presented for the determination of Mo isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) in geological samples. The method is based on the separation of Mo by extraction chromatography using N-benzoyl-N-phenylhydroxylamine (BPHA) supported on a microporous acrylic ester polymeric resin (Amberlite CG-71). By optimising the procedure, Mo could be simply and effectively separated from virtually all matrix elements with a single pass through a small volume of BPHA resin (0.5 ml). This technique for separation and enrichment of Mo is characterised by high selectivity, column efficiency and recovery (~100%), and low total procedural blank (~0.18 ng). A 100 Mo-97 Mo double spike was mixed with samples before digestion and column separation, which enabled natural mass-dependent isotopic fractionation to be determined with a measurement reproducibility of < 0.09‰ (d 98/95 Mo, 2s) by MC-ICP-MS. The mean d 98/95 Mo SRM 3134 (NIST SRM 3134 Mo reference material; Lot No. 891307) composition of the IAPSO seawater reference material measured in this study was 2.00 ± 0.03‰ (2s, n = 3), which is consistent with previously published values. The described procedure facilitated efficient and rapid Mo isotopic determination in various types of geological samples. Une nouvelle m ethode de pr e-concentration est pr esent ee pour la d etermination des rapports isotopiques du Mo par spectrom etrie de masse a source plasma et multi-collection (MC -ICP-MS) dans des echantillons g eologiques. La m ethode est bas ee sur la s eparation du Mo par Chromatographie d'extraction en utilisant du Nbenzoyle-N-ph enylhydroxylamine (BPHA) support e par une r esine polym ere d'ester acrylique microporeuse (Amberlite CG-71). En optimisant la proc edure, le Mo peutêtre simplement et efficacement s epar e de la quasitotalit e des el ements de la matrice avec un seul passage a travers un petit volume de r esine BPHA (0,5 ml). Cette technique de s eparation et d'enrichissement du Mo est caract eris ee par une grande s electivit e, une grande efficacit e et une grande r ecup eration de la colonne (~100%), et un faible total de la proc edure de blanc (~0,18 ng). Un double spike Mo 100 -Mo 97 a et e m elang e avec les echantillons avant la digestion et la s eparation sur colonne, ce qui a permis la d etermination du fractionnement isotopique naturel d ependant de la masse avec une reproductibilit e de mesure de < 0,09 ‰ ( d98/95 Mo, 2s) par MC -ICP-MS. La composition moyenne d 98/95 Mo SRM3134 (mat eriau de r ef erence NIST SRM 3134 Mo; Lot n°891307) de l'eau de mer de r ef erence IAPSO mesur ee dans cette etude est de 2,00 ± 0,03 ‰ (2s, n = 3), ce qui est coh erent avec les valeurs pr ec edemment publi ees. La proc edure d ecrite facilite une d etermination efficace et rapide des rapports isotopiques du Mo dans divers types d' echantillons g eologiques.