Positive Thermal Ionization Mass Spectrometry Research Articles

Determination of Stable Chlorine Isotopes by Isotopic Preparative Chromatography (IPC) with Positive–Thermal Ionization Mass Spectrometry (P-TIMS)

A novel approach to chlorine isotope analysis is presented to overcome many drawbacks of existing methods. Contemporary methods often require several laborious off-line procedures prior to instrumental determination; interfering ions (SO4 2- and NO3 -) in real samples are difficult to completely remove, especially when the concentrations of those ions are equal to that of the Cl- ion. This study was aimed to develop an automatic sample preparation method with chromatographic purity for determination of chlorine isotopes using isotopic preparative chromatography (IPC), which was a modified ion chromatograph and a fraction collector. An AS19 chromatographic column was employed to separate chlorine from interference ions using an eluent, flow rate, and suppressor current of 30 mM NaOH, 1 mL/min, and 70 mA, respectively. After the original solutions introduced into the IPC, eluted pure chlorine in the form of HCl was collected in an automated procedure from the outlet of the detector for 6 to 10 mins. The recoveries of chlorine were more than 95% with the relative standard deviation (RSD) of the separation less than 1.8%. After transforming the HCl into CsCl with a resin and concentration in a super-clean laboratory, the samples were sent to the thermal ionization mass spectrometer. The present method was validated by certified reference materials and real samples. The precision of 37Cl/35Cl ratio value was generally below 0.20 ‰. This method provides a potential approach for the analysis of samples with low chlorine concentrations.

Study on effect of sodium based buffers on the isotopic measurement of boron using Na2BO2+ by thermal ionization mass spectrometry

Alkali metaborate ions are usually monitored for the isotopic measurement of boron by positive thermal ionization mass spectrometry. Large variations in the of 10B/11B isotopic ratios are observed with the change in the mole ratios of B/Na when sodium carbonate solutions are added when compared with solution of neutral salt of sodium (NaCl). To understand the reason for the variations observed in the isotopic ratio of 10B/11B with the change in the mole ratio of B/Na, various sodium containing buffers effective in the pH range 3–9 were employed in the present studies instead of the conventionally used sodium carbonate for formation of Na2BO2+ ions in the ion source. NIST SRM-951 having certified 10B/11B ratio 0.2473 ± 0.0002 was used for all isotopic measurements by TIMS. It could be concluded that irrespective of the pH, the foremost reason for variations in the isotopic ratio of 10B/11B is the amount of Na present as Na2O on the filament.

Determination of boron content and isotopic composition in gypsum by inductively coupled plasma optical emission spectroscopy and positive thermal ionization mass spectrometry using phase transformation

As a stable isotope, boron plays an important role in hydrogeology, environmental geochemistry, ore deposit geochemistry and marine paleoclimatology. However, there is no report of boron isotopic composition in gypsum. This is mainly confined to complete dissolution of Gypsum by water or acid. In this study, gypsum was converted to calcium carbonate (CaCO3) with ammonium bicarbonate(NH4HCO3) by two steps at 50°C. In every step, the mass ratio of NH4HCO3/CaSO4·2H2O was twice, and conversion rate reached more than 98%. Converted CaCO3 was totally dissolved with hydrochloric acid (the dissolution rate was over 99%). In order to overcome the difficulties of the matrix interference and the detection limit of Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), we use Amberlite IRA 743 resin to purify and enrichment the boron at first, then eluting boron from the resin with 10mL 0.1mol/L hydrochloric acid at 75°C. The boron isotopic composition of natural gypsum samples was determined using positive thermal ionization mass spectrometry (P-TIMS). The boron isotopic composition of gypsum may be an excellent indicator for the formation environment.

High Precise Determination of Bromine Isotopic Ratios by Positive Thermal Ionization Mass Spectrometry Using Static Multicollection Based on Cs2Br+ Ions

Abstract A high precise determination of stable bromine (Br) isotopic ratios was achieved by thermal ionization mass spectrometer (TIMS) triton with 8 kV accelerating voltage using static multicollection of Cs2Br+ ions. The effect of B and Cl content on the measurement of Br isotope was studied. The static multicollection method had many advantages, such as high precision (external accuracy lies between 0.09‰–0.18‰), small amount of sample loading (10–20 μg Br) and short acquisition time (just 8 min for 100 cycles). The results showed that the effect of co-existing Cl on the measurement of Br isotope ratio increased with the increase of Cl content, and that the presence of B made the determined bromine isotope ratio lower than that without B. The effect of the sample loading sequence on the results of the determined Br isotopic ratio was insignificant. Meanwhile, the four bromide of Br isotopic composition were determined, its δ81Br was between 0.61‰–1.68‰, showing a significant Br isotope fractionation.

Separation and analysis of chlorine isotopes in higher plants

A novel chemical mass spectrographic method was used in the determination of chlorine (Cl) isotopes in plant tissues. The procedure includes dry ashing, three-step ion chromatographic separation of Cl isotopes, and isotope ratio determination based on Cs2Cl+ ion in positive thermal ionization mass spectrometry. The recovery of the method and the fractionation of Cl isotopes were validated using certified reference standard materials. The pretreatment strongly eliminated the effects of organic impurities and other anionic interferences, especially soluble nitrates and sulfates. The results show that there was severe fractionation of Cl isotopic composition in the tissues of plant samples, which might be caused by different molecular mechanisms of uptake and translocation of Cl within plants. The observed Cl isotopic variation is considered to be a useful isotope signature of living systems, which may be used to understand better the Cl cycling process in the environment.

Role of graphite in isotopic analysis of boron in metal boron alloys by Positive-Thermal Ionization Mass Spectrometry (P-TIMS)

Isotopic composition of boron in alloy samples was determined by Positive-Thermal Ionization Mass Spectrometry (P-TIMS) using Rb2BO2+. The titanium based boron alloy sample was treated with nitric acid to bring it to slurry form which was fused with rubidium carbonate on the high purity Rhenium filament for the formation of borate. Control of pH was found necessary to be necessary for both the formation of alkali borate compound as well as for obtaining good yield Rb2BO2+. Alkaline conditions were required for the formation of rubidium borate during fusion though neutral pH favored formation of Rb2BO2+ ions in the ion source. The sample loading procedure was suitably modified to obtain good ion intensities for Rb2BO2+ for high precision analysis. Steady ion beam was obtained when graphite was loaded on the filament after fusion of alloy carbonate mixture contrary to the reverse procedure that is normally followed. Sequence of graphite addition on the filament plays an important role in the formation of Rb2BO2+ ions. The paper gives the details of the investigations carried out.

Accurate and Precise Determination of Boron Isotopic Ratios at Low Concentration by Positive Thermal Ionization Mass Spectrometry Using Static Multicollection of Cs2BO2+ Ions

A static double-collector system for accurate, precise, and rapid boron isotope analysis has been established by employing a newly fixed Faraday H3 and H4 cup enabling simultaneously collected Cs2BO2(+) ion beams (m/z = 308 and 309) on a Finnigan-MAT Triton thermal ionization mass spectrometer of boron (Triton B). The experimental result indicated that Cs2BO2(+) ion beams (m/z = 308 and 309) were simultaneously collected using a fixed Faraday H3 and H4 cup without using the "Zoom Quad" function and reduced accelerating voltage. Furthermore, the method enabled the measurement of samples containing as little as 20 ng of boron. An analysis of the National Institute of Standards and Technology standard reference material (NIST SRM) 951 standard showed external reproducibility (2RSD) of ±0.013‰, ± 0.013‰, and ±0.019‰ for 100, 50, and 20 ng of boron, respectively. The present method of static multicollection of Cs2BO2(+) ions is applicable to a wide field of boron isotopic research that requires high precision and accuracy to analyze samples with low boron concentrations, including pore fluids, foraminifera, rivers, rainwater, and other natural samples.

The preparation and use of synthetic isotope mixtures for testing the accuracy of the PTIMS method for 10B/11B isotope ratio determination using boron mannitol complex and NaCl for the formation of Na2BO2+

The development of a method for determination of isotopic composition requires calibration of the method over a wide range of isotopic ratios. Further, validation of data obtained by the method requires isotopic reference materials spanning a wide range of ratios. In the present studies, gravimetric synthetic mixtures of boron with 10% 10B to 95% 10B were prepared by mixing solutions of enriched boron isotopes. The solutions of 10B and 11B enriched isotopes were calibrated using isotopic reference material NIST SRM-951 as a spike for isotope dilution. 10B/11B atom ratios in all the blends were determined by Positive Thermal Ionization Mass Spectrometry (PTIMS) using NaCl with mannitol for the formation of Na2BO2+. A measurement precision of about 0.03% was obtained from repetitive P-TIMS analyses of the mixtures with 10B content ranging from 10 to 70%. An instrument isotope fractionation factor (K-factor) of 0.99935 ± 0.00030 (1 s) was obtained for 10B/11B atom ratios of the different blends and this agreed with the K-factor determined from P-TIMS analysis of NIST SRM-951. The different isotopic blends prepared were also used in Inductively Coupled Plasma Quadrupole Mass Spectrometry, (ICP-QMS) employing NIST SRM-951 (10B/11B ratio of 0.2473) as a bracketing standard. An accuracy and precision of about 0.5% was obtained during ICP-QMS analyses of these mixtures. A novel and simple method for validation of analysis methodology with synthetic mixtures prepared using enriched isotopes is described in the present work.

Positive Thermal Ionization Mass Spectrometric Analysis of Boron Isotope on River/Rain Water with Low Content and Rich Organic Matter

A method for separation and isotopic determination of boron with low content and rich organic matter in the river/rain water samples was developed. Samples were concentrated by ion exchange Amberlite IRA-743 resin. The concentrated solution was subsequently micro-sublimated for 12 h to eliminate the organic matters. Then the boron isotope ratio was determined by measuring positive Cs(2)BO(2)(+) thermal ions. The average recovery was between 97. 5% and 101. 2%. The results that were determined by positive thermal ionization mass spectrometry were closed to those by MC-ICP-MS. The precision of isotopic measurement for boron in river/rain water was better than 0. 05 parts per thousand. The results demonstrated that this method was extremely effective for elimination organic matter interference during boron isotopic analysis with low sample size, high precision and accuracy.

Effective elimination of organic matter interference in boron isotopic analysis by thermal ionization mass spectrometry of coral/foraminifera: micro‐sublimation technology combined with ion exchange

In order to better estimate the effectiveness of micro-sublimation technology on the elimination of organic matter interference during boron isotopic analysis, a series of improved experiments was carried out using simple apparatus. Recovery rates after micro-sublimation were measured for boric acid solutions with different B contents or different B/organic matter ratios. The improved micro-sublimation procedure combined with ion-exchange technology was then used to test natural samples (coral and foraminifera) for the separation of boron. Our results show that the time taken for 100% recovery of different amounts of B differed and that the proportions of B/organic matter within the natural organic matter have little effect on the relationship between the recovery rates of B and the micro-sublimation times. The experiments further confirm that the organic matter does indeed have an effect on boron isotope analyses by positive thermal ionization mass spectrometry and that the use of micro-sublimation can effectively remove interferences from the organic matter during boron isotopic analysis.

Quantifying the pH ‘vital effect’ in the temperate zooxanthellate coral Cladocora caespitosa: Validation of the boron seawater pH proxy

Boron isotopic and elemental systematics are used to define the vital effects for the temperate shallow water Mediterranean coral Cladocora caespitosa. The corals are from a range of seawater pH conditions (pHT ~7.6 to ~8.1) and environmental settings: (1) naturally living colonies harvested from normal pH waters offshore Levanto, (2) colonies transplanted nearby a subsea volcanic vent system, and (3) corals cultured in aquaria exposed to high (700μatm) and near present day (400μatm) pCO2 levels. B/Ca compositions measured using laser ablation inductively coupled mass spectrometry (LA-ICPMS) show that boron uptake by C. caespitosa cultured at different pCO2 levels is independent of ambient seawater pH being mainly controlled by temperature-dependent calcification. In contrast, the boron isotope compositions (δ11Bcarb) of the full suite of corals determined by positive thermal ionisation mass spectrometry (PTIMS) shows a clear trend of decreasing δ11Bcarb (from 26.7 to 22.2‰) with decreasing seawater pH, reflecting the strong pH dependence of the boron isotope system. The δ11Bcarb compositions together with measurements of ambient seawater parameters enable calibration of the boron pH proxy for C. caespitosa, by using a new approach that defines the relationship between ambient seawater pH (pHsw) and the internally controlled pH at the site of calcification (pHbiol). C. caespitosa exhibits a linear relationship between pHsw and the shift in pH due to physiological processes (ΔpH=pHbiol−pHsw) giving the regression ΔpHClad=4.80−0.52×pHsw for this species. We further apply this method (“ΔpH–pHsw”) to calibrate tropical species of Porites, Acropora, and Stylophora reported in the literature. The temperate and tropical species calibrations are all linearly correlated (r2>0.9) and the biological fractionation component (ΔpH) between species varies within ~0.2 pH units. Our “ΔpH–pHsw” approach provides a robust and accurate tool to reconstruct palaeoseawater pHsw for both temperate and tropical corals, further validating the boron fractionation factor (αB3–B4=1.0272) determined experimentally by Klochko et al. (2006) and the boron isotope pH proxy, both of which have been the foci of considerable debate.

ChemInform Abstract: Boron Isotope Determinations in Waters and Other Geological Materials: Analytical Techniques and Inter‐Calibration of Measurements

AbstractReview: 69 refs.

High-precision isotopic analysis of boron by positive thermal ionization mass spectrometry with sample preheating

We present a methodology for the precise and accurate analysis of boron isotope ratios (11B/10B) by positive thermal ionization mass spectrometry (P-TIMS) using Cs2BO2+ ions. Samples in the form of caesium borate were loaded onto Ta filaments together with graphite and mannitol. The addition of mannitol to the samples is essential to suppress boron volatilization during acid treatment of the samples but is known to lower the performance of P-TIMS. Therefore, the prepared filaments were preheated in an oven at 240 °C to eliminate the mannitol thus stabilizing the chemical species of boron on the filament and increasing the ionization efficiency of Cs2BO2+, which enabled high-precision isotopic analysis of boron with small sample sizes. Analyses of NIST SRM 951 standard showed external reproducibility (2RSD) better than ±0.1‰ for 50–100 ng B and ±0.2‰ for 10 ng B. Ultrafiltration followed by cation- and anion-exchange chromatography was used to chemically separate boron from natural samples. Analyses of coral standard GSJ JCp-1 and seawater standard IRMM BCR-403 gave average δ11B values of +24.25 ± 0.08‰ and +39.58 ± 0.11‰ (2SD), respectively. The P-TIMS method developed in this study is applicable to a wide field of boron isotopic research that requires high precision and accuracy, including paleo-pH studies using marine carbonate samples.

High precision isotope ratio measurements on by thermal ionization mass spectrometry using ion.

Studies were carried out to determine the 10B/11B isotope ratio by positive thermal ionization mass spectrometry (P-TIMS) analyzing boron as rubidium borate ions. Of the 36 different ionic species formed, the boron and rubidium isotope ratios were obtained from the ion intensity ratios of the most suitable ion pairs corresponding to masses 212, 213 and 215, 213 respectively. The investigations were carried out to explore the possibility of correcting the observed isotope ratio of boron by using a modified internal normalization technique based on the observed Rb isotope ratio. The method is based on the relation of isotopic fractionation of boron as a function of the rubidium (natural isotopic composition) isotopes fractionation obtained during TIMS analysis from the same filament loading. The application of the methodology to improve the precision of the observed 10B/11B isotope ratio during analysis of irradiated boron alloy samples is demonstrated. Improvement in precision from 0.25% to better than 0.05% was demonstrated using this approach.

Measurement of chlorine stable isotopic composition by negative thermal ionization mass spectrometry using total evaporation technique

A total evaporation negative thermal ionization mass spectrometry (TE-N-TIMS) technique for the isotopic analysis of chlorine was developed. This technique provides fast and reliable way to determine the isotopic signature of chlorine samples as small as 100 ng. Compared to the conventional N-TIMS method, the precision of the Cl isotopic analysis is improved by a factor of up to 3 by minimizing the effect of mass fractionation. Using this method, reproducibility of 0.9‰ (R.S.D.: n = 25) can be achieved for 37Cl/35Cl ratio of 200 ng Cl. The analyzed results of the AgCl reagent expressed as a per-mil deviation (δ37Cl) relative to the Standard Mean Ocean Chloride showed good concordance with the value obtained by conventional positive thermal ionization mass spectrometry (P-TIMS).

Boron isotope determinations in waters and other geological materials: Analytical techniques and inter-calibration of measurements†

The 11B/10B ratio exhibits wide variations in nature; thus, boron isotopes have found numerous applications in geochemistry, hydrology, and environmental studies. The main analytical techniques used are as follows: positive thermal ionisation mass spectrometry is the most precise (about 0.2‰ of the boron isotope ratio), but requires complex and laborious sample preparation; negative thermal ionisation mass spectrometry is less precise (about 0.5‰), but rapid and suitable for water samples, whereas total evaporation-NTIMS allows for identification of the precise boron isotope composition of marine carbonates. It is expected that multi-collection system inductively coupled plasma mass spectrometry (MC-ICPMS) will eventually combine high precision with simple analytical procedures. Secondary ion mass spectrometry and laser ablation (LA)-MC-ICPMS allow in situ determinations on solid samples, but require the availability of calibration materials which are chemically and mineralogically similar to samples. These features of boron isotope measurement techniques were confirmed by the results of the first inter-laboratory comparison of measurements, organised by the Istituto di Geoscienze e Georisorse in Pisa. Finally, two examples of boron isotope applications in groundwater investigations are reported. †Updated paper: originally presented on the IAEA International Symposium “Quality Assurance for Analytical Methods in Isotope Hydrology” (August 2004, Vienna).

A robust methodology for high precision isotopic analysis of boron by thermal ionization mass spectrometry using Na 2BO 2+ ion

A detailed study to develop a robust methodology for determining 11B/ 10B isotope ratio using sodium metaborate (Na 2BO 2 +) in positive thermal ionisation mass spectrometry (P-TIMS) was performed. Different parameters of sample preparation and sample loading procedure, using single tantalum filament assembly, were optimized and their effects on ion intensity and precision in isotope ratio were evaluated. A comparative evaluation of precision achievable using Na 2CO 3 and NaCl to adjust the B/Na mole ratio in the sample was also carried out. This was done to confirm the robustness of the approach for analysing different kinds of sample matrices e.g., solids and solutions which require chemical purification and pre-concentration prior to TIMS analysis. NIST isotopic reference material SRM-951 with 11B/ 10B isotope ratio of 4.044 ± 0.003 was used for various experiments. Loading of boron in the form of boromannitol complex along with sodium carbonate (for solid samples) and with NaCl (for solutions) on the graphite coated single tantalum filament assembly was found to give high precision (better than 1‰) in the isotope ratios using 500 ng to 1 μg of boron. The results were not influenced by variations in the B/Na mole ratio, which is an important aspect of using this methodology for analyzing unknown samples. Robustness of the developed methodology is demonstrated by analyzing solid samples as well as solutions for boron isotopic composition.

Evidence for ocean acidification in the Great Barrier Reef of Australia

Geochemical records preserved in the long-lived carbonate skeleton of corals provide one of the few means to reconstruct changes in seawater pH since the commencement of the industrial era. This information is important in not only determining the response of the surface oceans to ocean acidification from enhanced uptake of CO 2, but also to better understand the effects of ocean acidification on carbonate secreting organisms such as corals, whose ability to calcify is highly pH dependent. Here we report an ∼200 year δ 11B isotopic record, extracted from a long-lived Porites coral from the central Great Barrier Reef of Australia. This record covering the period from 1800 to 2004 was sampled at yearly increments from 1940 to the present and 5-year increments prior to 1940. The δ 11B isotopic compositions reflect variations in seawater pH, and the δ 13C changes in the carbon composition of surface water due to fossil fuel burning over this period. In addition complementary Ba/Ca, δ 18O and Mg/Ca data was obtained providing proxies for terrestrial runoff, salinity and temperature changes over the past 200 years in this region. Positive thermal ionization mass spectrometry (PTIMS) method was utilized in order to enable the highest precision and most accurate measurements of δ 11B values. The internal precision and reproducibility for δ 11B of our measurements are better than ±0.2‰ (2 σ), which translates to a precision of better than ±0.02 pH units. Our results indicate that the long-term pre-industrial variation of seawater pH in this region is partially related to the decadal–interdecadal variability of atmospheric and oceanic anomalies in the Pacific. In the periods around 1940 and 1998 there are also rapid oscillations in δ 11B compositions equivalent changes in pH of almost 0.5 U. The 1998 oscillation is co-incident with a major coral bleaching event indicating the sensitivity of skeletal δ 11B compositions to loss of zooxanthellate symbionts. Importantly, from the 1940s to the present-day, there is a general overall trend of ocean acidification with pH decreasing by about 0.2–0.3 U, the range being dependent on the value assumed for the fractionation factor α (B3–B4) of the boric acid and borate species in seawater. Correlations of δ 11B with δ 13C during this interval indicate that the increasing trend towards ocean acidification over the past 60 years in this region is the result of enhanced dissolution of CO 2 in surface waters from the rapidly increasing levels of atmospheric CO 2, mainly from fossil fuel burning. This suggests that the increased levels of anthropogenic CO 2 in atmosphere has already caused a significant trend towards acidification in the oceans during the past decades. Observations of surprisingly large decreases in pH across important carbonate producing regions, such as the Great Barrier Reef of Australia, raise serious concerns about the impact of Greenhouse gas emissions on coral calcification.

Instability of seawater pH in the South China Sea during the mid-late Holocene: Evidence from boron isotopic composition of corals

We used positive thermal ionization mass spectrometry (PTIMS) to generate high precision δ 11B records in Porites corals of the mid-late Holocene from the South China Sea (SCS). The δ 11B values of the Holocene corals vary significantly, ranging from 22.2‰ to 25.5‰. The paleo-pH records of the SCS, reconstructed from the δ 11B data, were not stable as previously thought but show a gradual increase from the Holocene thermal optimal and a sharp decrease to modern values. The latter is likely caused by the large amount of anthropogenic CO 2 emissions since the Industrial Revolution but variations of atmospheric pCO 2 cannot explain the pH change of the SCS before the Industrial Revolution. We suggest that variations of monsoon intensity during the mid-late Holocene may have driven the sea surface pH increase from the mid to late Holocene. Results of this study indicate that the impact of anthropogenic atmospheric CO 2 emissions may have reversed the natural pH trend in the SCS since the mid-Holocene. Such ocean pH records in the current interglacial period can help us better understand the physical and biological controls on ocean pH and possibly predict the long-term impact of climate change on future ocean acidification.

Isotope fractionation studies of molybdenum

Mass spectrometric studies of the isotopic composition of molybdenum have become an active area of research in stable isotope geochemistry, biogeochemistry and cosmochemistry. The redox chemistry of Mo, together with its proclivity for covalent bonding, indicates its importance in isotope fractionation studies such as palaeoceanography. The measurement of the magnitude of isotope fractionation of Mo in natural systems is a challenging task, in that natural fractionation has to be carefully distinguished from chemical and instrumental isotope fractionation. An ion exchange chemical separation procedure has been developed with high efficiency and low blank, to ensure that the isobaric elements Zr and Ru are removed from the samples before mass spectrometric analysis. The isotope fractionation resulting from this procedure is 0.14‰ per u. The isotopic composition of Mo of a Laboratory Standard has been measured by positive and negative thermal ionization mass spectrometry (P-TIMS and N-TIMS, respectively), to give an isotope fractionation of 6.4‰ and 0.5‰ per u, respectively, with respect to the absolute isotope abundances of Mo. In both cases the lighter isotopes are enhanced with respect to the heavier isotopes. An ascorbic acid activator has enabled the sensitivity of P-TIMS to be improved as compared to traditional methods. The same experiment was repeated using a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) to give an isotope fractionation of approximately 17.0‰ per u. In this case the heavier isotopes are enhanced with respect to the lighter isotopes. The strengths and weaknesses of these three mass spectrometric techniques are evaluated. We conclude that MC-ICP-MS is the optimum mass spectrometric method for accurately measuring the isotope fractionation of Mo in natural materials, provided chemical and instrumental isotope fractionation can be resolved from naturally induced isotope fractionation. There is an urgent need for an internationally accepted calibrated reference material to be developed. Our Laboratory Standard has recently been calibrated at Curtin University by measurements of gravimetric mixtures of two enriched isotopes of Mo, to obtain the absolute isotope abundances of Mo. This Laboratory Standard can be made available to those laboratories in which isotopic studies of Mo are executed, to enable meaningful inter-laboratory comparisons to be conducted.