Isobaric Interference Correction Research Articles

LA-ICP-Q-MS/MS Re[sbnd]Os geochronology: A comparison of N2O and CH4 reaction gases

The ReOs isotope system can directly date sulphide formation, making it useful for ore deposit studies. Recent work has demonstrated that laser ablation inductively coupled tandem mass spectrometry (LA-ICP-MS/MS) can be used to effectively separate 187Re from 187Os during analysis by reacting Os with CH4 gas, allowing for in situ ReOs age determination of molybdenite. However, the age calculation often requires a significant interference correction of 187ReCH2+ on 187OsCH2+. Here, we demonstrate that N2O gas is a viable alternative reaction gas for in situ ReOs geochronology. In this new method, Os forms a tetra-oxide complex, while Re shows very low reactivity with the N2O reaction gas (∼0.15 %), reducing the isobaric interference correction requirement relative to the CH4 method. We compare results from both reaction gases across a range of molybdenite samples of different ages (spanning ca. 1700–300 Ma), demonstrating that the N2O method achieves greater precision and accuracy for young molybdenite samples (ca. 300 Ma) compared to CH4. In addition, we demonstrate that in situ ReOs is capable of dating high-Re pyrite (i.e., >10 ppm).

In situ Lu–Hf dating of allanite by LA-ICP-MS/MS: Implications for geochronology

Allanite is a common REE-rich accessory mineral found in various igneous and metamorphic rocks, and can record a variety of geological processes. Therefore, allanite geochronology has the potential to answer a range of important geological questions. Allanite U–Th–Pb geochronology is hampered by common open-system behavior in the system. In this study, we demonstrate the feasibility of in situ allanite Lu–Hf dating by LA–ICP–MS/MS. A total of nine allanite samples from different rock types (e.g., granite, pegmatite) were investigated. These allanite samples have ages ranging from ca. 2650 to ca.100 Ma, and Lu contents ranging from several to hundreds of μg g−1 levels and relatively high Lu/Hf ratios (> 30). At a mass shift of +82, the isobaric interferences 176Lu and 176Yb have extremely low reaction rates of ∼0.003 % and ∼ 0.0003 %, respectively, indicating the isobaric interference corrections are insignificant for the allanite samples (mean 175Lu/177Hf = ∼814; mean 172Yb/177Hf = ∼719). A two-step calibration strategy was proposed for the 176Lu/176Hf and 177Hf/176Hf ratio corrections using NIST SRM 610 (for instrument drift) and LE2808 (for matrix effect). The nine allanite samples contain common Hf contents (f176Hf) of ∼5 % to >90 %, and the data are plotted in inverse isochron diagrams. Unanchored inverse isochron ages exhibit a large deviation in accuracy (5–10 %), whilst anchored isochron ages have a better accuracy of <5 %. The uncertainty of anchor initial 176Hf/177Hf values was investigated and, in general, was insignificant (< 2.8 %) for samples with f176Hf < 80 %. Our results demonstrate that in situ allanite Lu–Hf dating by LA-ICP-MS/MS is feasible and can yield precise and accurate ages (< 5 %). Lu–Hf geochronometer captures the high-temperature process and may be more resistant during the late thermal event. Thus, it provides an alternative solution for those samples which are suffered by open-system behavior in U-Th-Pb system.

In situ Fe isotope analysis of Cr-rich iron oxides using pure chromium metal for isobaric interference corrections by femtosecond LA–MC–ICP–MS

Iron oxide minerals, such as hematite and magnetite, are commonly found in a wide range of geological environments. Their Fe isotopic composition acts as a potent geochemical tracer, finding applications across various realms of Earth sciences. However, natural iron oxide minerals often have a high Cr content up to percentile levels, necessitating correction of isobaric interference caused by 54Cr+ on 54Fe+ to ensure accurate and precise in situ Fe isotopic compositions. In this study, a pure chromium metal with homogeneous isotopic compositions was examined within the analysis sequence to obtain the fractionation factor of Cr (βCr) for isobaric interference correction. A femtosecond laser ablation system combined with wet plasma conditions was used to decrease the matrix effect. We synthesized a series of magnetite and hematite samples with simple matrix as well as natural magnetite samples with complex matrix to evaluate the feasibility of Cr interference correction. By employing our proposed correction method, the deviation caused by the isobaric interference of 54Cr+ was effectively eliminated. The corrected δ56Fe values for hematite and magnetite samples, even with a Cr/Fe ratio of as high as 1.27, exhibited good agreement with the reference values within the long-term reproducibility uncertainty of 0.10‰. These results indicate the robustness of Cr interference correction in obtaining accurate Fe isotopic compositions of Cr-rich iron oxides.

A method for background correction in 10Be detection: Evaluation of indirect isobaric interference by 7Be generated at the entrance window of a gas counter

This report presents a procedure for background correction of indirect isobaric interference by 10B in accelerator mass spectrometry of cosmogenic 10Be. A gas counter with an absorber cell for 10B is used as a detector. Injected ions are detected by two anode plates aligned in the main ionization chamber to plot the signals on a two-dimensional spectrum of loss and residual energies. Using this configuration, the tail of 10B events that manage to pass through the absorber cell can be separated from the 10Be events, but the total counts in the 10Be region are increased by 7Be generated from the reaction of 10B(1H,4He)7Be due to hydrogen attached on the surface of the entrance window of the absorber cell. Since the number of 7Be events are proportional to the counts of 4He events, we can evaluate the interference via statistical analyses for correlations between counting data for multiple regions of interest on the two-dimensional spectra. This correction results in an increase in uncertainty for the counting statistics, but improves the accuracy of the maximum likelihood value of the 10Be/9Be isotopic ratios.

Determination of the Isotopic Composition of Ytterbium by MC-ICP-MS Using an Optimized Regression Model.

In this study, we measure the absolute isotope ratios of ytterbium (Yb) by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using an optimized regression model for mass bias correction. A rhenium (Re) reference material (NIST SRM 3143), which has been characterized previously, is selected as a primary calibrator to calibrate the absolute Yb isotope ratios for three Yb materials (GSB, Alfa Yb, and GBW). The three-isotope plot for all collected data indicates that the results of Yb isotope ratios obtained are not affected by any polyatomic interferences and the mass-independent isotopic fractionation. Furthermore, the recalibrated Hf historical isotope ratios by using the absolute Yb isotopic composition obtained in this study for the isobaric interference correction on Hf isotopes are in agreement with the original historical values. This work has further demonstrated the applicability of the regression model for the calibrated measurements of absolute isotope ratios using MC-ICP-MS. The three mono-elemental Yb standard solutions are thus proposed as the reference materials for Yb isotope ratio measurements in environmental and geoscience applications.

Interferences and Matrix Effects on Iron Isotopic Composition Measurements by 57Fe-58Fe Double-Spike Multi-Collector Inductively Coupled Plasma Mass Spectrometry; the Importance of Calcium and Aluminum Interferences

Multi-collector inductively coupled plasma mass spectrometers (MC-ICPMS) are widely used for Fe isotope measurements. The latter may be perturbed by interferences (notably from Cr and Ni) and matrix effects (notably from major elements), caused by elements remaining in the samples after purification. We quantified some of these perturbations and our ability to correct them whenever possible, using Thermo Neptune and Neptune Plus MC-ICPMS with a 57-58Fe double-spike mass bias correction. 54Cr and 58Ni isobaric interference corrections were found to be extremely efficient up to Cr/Fe=0.12 and Ni/Fe=0.04 (g/g natural Fe). Matrix effects were found negligible up to at least Na/Fe=175, Mg/Fe=10, K/Fe=1.5, and Mo/Fe=75 (g/g natural Fe). 28Si2+ interference was found negligible up to Si/Fe=50. Finally, we found that calcium and aluminum could cause significant interferences (e.g., 40Ca16O and 27Al2+), for Ca/Fe ≥ 2.5 and Al/Fe ≥ 2.5. The perturbation intensity relative to the Ca/Fe ratio was found dependent on the measurement conditions (plateau width). While working with samples with potentially high calcium or aluminum contents (such as calcite minerals or tests, bones and teeth, or marine samples and crustal rocks), we recommend to carefully take into account Ca and Al while tuning the instrument and checking the measurement accuracy with isotopic standards (i.e., doping the isotopic standard with Ca and Al levels comparable to those of the samples).

In situ Fe isotopic analyses of fourteen reference materials using a synthetic Cr standard for mass bias and isobaric interference corrections by femtosecond LA-MC-ICP-MS

A new method for the direct determination of Fe isotopic compositions in silicate rock samples by fs LA-MC-ICP-MS.

Precise δ88/86Sr determination on a MC-ICP-MS by an improved method combining Zr-empirical external normalization isobaric interference correction and 84Sr–87Sr double spike

Zr-EEN isobaric interference correction coupled with the 84Sr–87Sr double spike method allows highly accurate and precise δ88/86Sr determination on a MC-ICP-MS.

Isobaric Spike Method for Absolute Isotopic Ratio Determination by MC-ICP-MS.

Absolute isotopic ratios are required for isobaric interference corrections, spike calibrations, and isotopic analysis by external normalization methods. However, high-precision natural isotopic abundance data are lacking for many elements, particularly those with less than four isotopes or having isobaric isotopes with other elements. In this study, we developed a method for absolute isotope ratio analysis, which integrates the concept of the double-spike method with isotopic analysis of element pairs that have isobaric isotopes. Using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS), the isotopic composition of a sample can be derived by measuring a series of mixtures of the sample and a spike element that has an isobaric isotope with the element being analyzed. We applied this method to five pairs of elements (Ca-Ti, V-Ti, Cr-Ti, Ni-Zn, and In-Sn) and obtained the absolute isotopic ratios for Ca, V, Cr, Ni, and In, as well as the relative Ca isotopic composition. By simultaneous measurement of Ti and Ca isotopes, a quantitative relationship between the instrumental mass fractionation factors and element masses was developed. After correcting for the difference in instrumental mass fractionation factors, the obtained absolute ratios agree well with the literature data and have per mil level accuracy. This method has considerable potential in measuring the absolute isotopic ratios of elements that have isobaric isotope with other elements. Such precisely determined absolute isotopic ratios and the relationship between the instrumental mass fractionation factors and elemental masses will improve isobaric interference corrections, particularly when chemical purification is imperfect or during laser ablation analysis.

Improved in-situ Determination of Sr Isotope Ratio in Silicate Samples Using LA-MC-ICP-MS and Its Wider Application for Fused Rock Powder

The in-situ Sr isotope determination of solid samples has the advantages of high spatial resolution and convenient and rapid sample preparation. However, due to the lack of column chemistry separation of matrix elements from Sr, the interference correction (especially the isobaric interference from 87Rb on 87Sr) becomes a big issue for high precise in-situ Sr isotope analytical results. In this study, we evaluated the influence of isobaric interference systematically and adopted an improved strategy for isobaric interference correction of Rb. Specifically, as an external standard for data calibration, an in-house silicate standard (Rb-std) was fused from pure oxide powders. The new standard (Rb-std) shows very low contents of Sr (<1 ppm), Yb (<0.09 ppm) and Er (<0.05 ppm), which directly avoid the trouble of interference of doubly charged ions and isobar, when we determinate the mass fractionation factors of Rb (βRb). Our improved method can provide more accurate data than previous researches, in which the mass fractionation were calculated from an external reference material StHs6/80-G with high Rb (30.07 ppm), Sr (482 ppm), Yb (1.13 ppm) and Er (1.18 ppm). Then, these βRb from Rb-std were applied by linear interpolation to the unknown samples for correction of 87Rb on 87Sr. The analytical results of serial international reference materials (BIR-1G, BCR-2G, BHVO-2G, T1-G and ATHO-G) demonstrate that our improved method can raise the upper limit of Rb/Sr for in-situ Sr isotope determination and reduce the relative standard deviation of results. This improvement of the upper limit of Rb/Sr (<0.33) will expand not only range of microanalysis for silicate minerals, but also bulk Sr isotope determination of volcanic rock combining with rapid fusion technique.

A new practical isobaric interference correction model for thein situHf isotopic analysis using laser ablation-multi-collector-ICP-mass spectrometry of zircons with high Yb/Hf ratios

An isobaric interference correction model was proposed for thein situHf isotopic analysis of zircons with high Yb/Hf ratios using LA-MC-ICP-MS.

Simple and cost-effective methods for precise analysis of trace element abundances in geological materials with ICP-MS

Inductively coupled plasma mass spectrometry (ICP-MS) is the most commonly used technique to determine the abundances of trace elements in a wide range of geological materials. However, incomplete sample digestion, isobaric interferences and instrumental drift remain obvious problems that must be overcome in order to obtain precise and accurate results. For this reason, we have done many experiments and developed a set of simple, cost-effective and practical methods widely applicable for precise and rapid determination of trace element abundances in geological materials using ICP-MS. Commonly used high-pressure digestion technique is indeed effective in decomposing refractory phases, but this inevitably produces fluoride complexes that create new problems. We demonstrate that the fluoride complexes formed during high-pressure digestion can be readily re-dissolved using high-pressure vessel at 190°C for only 2h for 50mg sample. In the case of isobaric interferences, although oxide (e.g., MO+/M+) and hydroxide (e.g., MOH+/M+) productivity is variable between runs, the (MO+/M+)/(CeO+/Ce+) and (MOH+/M+)/(CeO+/Ce+) ratios remain constant, making isobaric interference correction for all other elements of interest straightforward, for which we provide an easy-to-use off-line procedure. We also show that mass-time-intensity drift curve is smooth as recognized previously, for which the correction can be readily done by analyzing a quality-control (QC) solution and using off-line Excel VBA procedure without internal standards. With these methods, we can produce data in reasonable agreement with recommended values of international rock reference standards with a relative error of <8% and precision generally better than 5%. Importantly, compared to the widely used analytical practice, we can effectively save >60% of time (e.g., <24h vs. >60h).

High-precision measurement of (186)Os/(188)Os and (187)Os/(188)Os: isobaric oxide corrections with in-run measured oxygen isotope ratios.

We present a novel method for high precision measurement of (186)Os/(188)Os and (187)Os/(188)Os ratios, applying isobaric oxide interference correction based on in-run measurements of oxygen isotopic ratios. For this purpose, we set up a static data collection routine to measure the main Os(16)O3(-) ion beams with Faraday cups connected to conventional 10(11) amplifiers, and (192)Os(16)O2(17)O(-) and (192)Os(16)O2(18)O(-) ion beams with Faraday cups connected to 10(12) amplifiers. Because of the limited number of Faraday cups, we did not measure (184)Os(16)O3(-) and (189)Os(16)O3(-) simultaneously in-run, but the analytical setup had no significant influence on final (186)Os/(188)Os and (187)Os/(188)Os data. By analyzing UMd, DROsS, an in-house Os solution standard, and several rock reference materials, including WPR-1, WMS-1a, and Gpt-5, the in-run measured oxygen isotopic ratios were proven to present accurate Os isotopic data. However, (186)Os/(188)Os and (187)Os/(188)Os data obtained with in-run O isotopic compositions for the solution standards and rock reference materials show minimal improvement in internal and external precision, compared to the conventional oxygen correction method. We concluded that, the small variations of oxygen isotopes during OsO3(-) analytical sessions are probably not the main source of error for high precision Os isotopic analysis. Nevertheless, use of run-specific O isotopic compositions is still a better choice for Os isotopic data reduction and eliminates the requirement of extra measurements of the oxygen isotopic ratios.

Re-evaluation of interferences of doubly charged ions of heavy rare earth elements on Sr isotopic analysis using multi-collector inductively coupled plasma mass spectrometry

We re-evaluate the interference of doubly charged heavy rare earth elements during Sr isotopic analysis using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). A series of mixed solutions of standard reference material SRM 987, rare earth elements, and Sr separated from rock reference materials are measured to assess the influence of isobaric interferences on the MC-ICP-MS analysis of Sr isotopes. After sample dissolution, conventional cation-exchange chromatography is employed for Sr purification of rock reference materials prior to MC-ICP-MS measurement. It has been demonstrated that if the natural abundances of Er and Yb are used to correct for doubly charged ion interferences on Sr, an overcorrection results. In contrast, the use of measured doubly charged ion ratios results in an accurate and precise correction of isobaric interference. This finding is confirmed by analytical results for several certified reference materials from mafic (basaltic) to felsic (granitic) silicate rocks. It is noteworthy that, because Er is more prone to doubly charged ion formation, it dominates over Yb doubly charged ions as an interference source.

Study of Isobaric Interference in Quantification of Citrulline by Parallel Fragmentation Monitoring.

Parallel Fragmentation Monitoring (PFM), which is an analogue of selected reaction monitoring (SRM), is a recently developed method for quantification of small molecules by MALDI-TOF/TOF mass spectrometry (MS). It is well known that isobaric interference substances can be occasionally present in complex biological samples, and affect the accuracy of measurement by SRM. Unfortunately, by design it is not possible to assess whether isobaric interference happens in a SRM analysis. In contrast, the unique design of PFM should allow quick inspection for isobaric interference and subsequent correction. In this study, using arginine as an example, interference effect of isobaric structural analogs on the quantification of citrulline by PFM was evaluated. Our results showed that the presence of arginine affected the measured concentrations of citrulline standard solutions in a concentration dependent manner. Such interference could be observed readily in the MS/MS spectra, and contributed by [arginine+H-NH3](+) fragment ion. Because of having highly similar mass, (13)C-isotope of [arginine+H-NH3](+) fragment ion overlapped with monoisotope of [citrulline+H-NH3](+) fragment ion, which was used as the report ion for quantification. However, such interference could be mathematically eliminated or minimized through estimation of the signal intensity of the (13)C-isotopic peak of [arginine+H-NH3](+) from the intensity of the corresponding monoisotopic peak according to isotope distribution of elements. Furthermore, the presence of interfering fragment ions could be avoided by optimizing MALDI ionization condition. In conclusion, isobaric interference can happen in PFM, but can be easily identified in the mass spectra and eliminated (minimized) with simple methods.

Guidelines for reporting zircon Hf isotopic data by LA-MC-ICPMS and potential pitfalls in the interpretation of these data

Technical Paper High quality analytical data are essential for the development of sound scientific interpretations. To ensure the quality of the data published in Chemical Geology, a new type of contribution has been introduced - the Invited Technical Paper. When a particular technical issue needing discussion or clarification is identified, specialists in the technique will be invited to share their expertise. As is true for all articles published in the journal, these contributions will be subject to peer review before publication. The first topic to be treated concerns in situ Hf isotopic measurements in zircon by laser ablation inductively coupled plasma mass spectrometry. This is an extremely powerful and promising technique that has been adopted by many laboratories throughout the world. However, if insufficient care is taken during analysis and data processing, inaccurate results can be obtained, notably because of the existence of very large isobaric interferences on the isotope of interest. To address this issue, we have asked Christopher Fisher, Jeffery Vervoort and John Hanchar to provide a set of guidelines that can be adopted to assure that reliable Hf isotopic data are obtained by this technique. Abstract Over the past decade, the Hf isotope composition of zircon, as determined in situ by laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS), has been applied increasingly to a wide range of geological problems and has proven to be a valuable analytical tool. There has been no uniformity, however, in the reporting of in situ Hf isotopic data and, quite often, reviewers and readers of papers are not provided with sufficient information to assess data quality. The goal of this invited contribution is to provide the non-specialist with a brief outline and explanation of what is required for proper presentation and documentation of in situ Hf isotopic data from zircon, including details of how the challenging large isobaric interference corrections have been made. In addition, we discuss a number of potential pitfalls vis-a-vis the assignment of the incorrect age to the measured Hf isotope composition. Non-specialists should be aware of these important issues when doing their own analyses and evaluating the analyses done by others.

Sm-Nd isotopic analysis of mixed standard solutions by multi-collector inductively coupled plasma mass spectrometry: evaluations on isobaric interference correction of Nd isotopic composition and external calibration of Sm/Nd ratio

Abstract Background The Sm-Nd isotope system has long been used to provide information on the age and geochemical evolution of terrestrial rocks and extraterrestrial objects. Traditional thermal ionization mass spectrometry requires a refined chemical separation of Sm and Nd. Here, we present multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) Sm-Nd isotopic results for a series of mixed standard solutions with different Sm/Nd ratios to test the validity of isobaric interference corrections of Nd isotopic composition and external calibration of Sm/Nd inter-elemental ratio. Findings Reliable 143Nd/144Nd and 145Nd/144Nd ratios of the mixed solutions were obtained by using the exponential law and selected Sm isotopic compositions. The Sm/Nd ratios of the mixed solutions corrected by the standard bracketing method were consistent with the gravimetric values mostly within 1% difference. Conclusions This study provides a simple and high-throughput technique that can simultaneously measure Nd isotopic composition and Sm/Nd ratio without chemical separation between Sm and Nd.

Hafnium isotope analysis of mixed standard solutions by multi-collector inductively coupled plasma mass spectrometry: an evaluation of isobaric interference corrections

Abstract Background The Lu-Hf isotope system is widely used to decipher the crustal evolution and mantle differentiation of the Earth. The most critical point in obtaining accurate Hf isotope data is to correct the isobaric interferences of Yb and Lu imposed on the 176Hf peak. In this study, we tested the validity of within-run correction protocol using MC-ICP-MS analysis of Hf standard solutions doped with Yb and Lu. Findings We found that the use of carefully selected Yb isotopic composition in the literature resulted in more reliable 176Hf/177Hf ratio. The 176Hf/177Hf ratios analyzed for a series of mixed Hf+Yb+Lu standard solutions could be quite accurately corrected for the mass bias and isobaric interferences. The systematic decreasing trend in the corrected 176Hf/177Hf ratios with increasing Yb/Hf ratios, however, indicates that the mass bias effect cannot be completely removed by the exponential law for samples high in Yb. Conclusions A close correlation of the calculated 176Yb/177Hf and 176Lu/177Hf ratios with the gravimetric values sheds light on the direct determination of inter-elemental isotope ratios without chemical purification.

Selenium isotope analysis of organic-rich shales: advances in sample preparation and isobaric interference correction

Selenium has a complex biogeochemical cycle with many similarities to that of sulfur. Fractionations of selenium isotopes induced in bacterial respiration reactions have been recognized as potential recorders of environmental oxidation states, opening up the possibility of further constraining bioproductivity and the redox evolution of the Earth's atmosphere and ocean over time. However, analyses of selenium isotopes are complicated by interferences with organic compounds as well as a number of isobaric interferences. Application of existing sample preparation protocols to geological samples replete with organic carbon can result in incomplete extraction yields and incomplete removal of isobarically interfering germanium and arsenic. We present measurements of three different organic-rich shales of varying ages prepared with eight different sample preparation protocols and identify a method with which high selenium yields are obtained for all three samples while the concentration of germanium is greatly reduced. We further investigate the quantitative importance of isobaric interferences and present new post-analytical data correction protocols. If selenium concentrations in standards and samples are matched to within 5%, the ratios of five isotopes of selenium (74Se, 76Se, 77Se, 78Se and 82Se) can be measured with precisions better than 0.2‰ for δ76/78Se, δ77/78Se and δ82/78Se and 0.5‰ for δ74/78Se, allowing analytical accuracy to be monitored with three-isotope diagrams and thus enabling the detection of any mass-independent isotopic fractionation.

Simultaneous Determination of143Nd/144Nd and147Sm/144Nd Ratios and Sm–Nd Contents from the Same Filament Loaded with Purified Sm–Nd Aliquot from Geological Samples by Isotope Dilution Thermal Ionization Mass Spectrometry

Isotope dilution thermal ionization mass spectrometry (ID-TIMS) is the standard technique used to achieve precise (143)Nd/(144)Nd and (147)Sm/(144)Nd isotope ratios and accurate elemental concentrations of Sm-Nd. However, in previous studies, purified Sm and Nd fractions must be individually loaded onto different filaments for their accurate determination using TIMS because of severe isobaric interferences. Thus, the classical ID-TIMS technique is time consuming and laborious. In this study, a new method is proposed, which is able to acquire both ratios of (143)Nd/(144)Nd and (147)Sm/(144)Nd and concentrations of Sm-Nd simultaneously on the same filament arrangement. The measurement time and filament consumption are reduced by 50% with the current method, and therefore, the operation cost of TIMS is significantly reduced. A mixed (152)Sm-(148)Nd spike was employed to achieve accurate results after spike subtraction and isobaric interference corrections. Results obtained from a series of standard rock samples are in good agreement with recommended values, within ±0.003% for the (143)Nd/(144)Nd ratio and ±1% for the (147)Sm/(144)Nd ratio.