Accurate U–Th radioactive disequilibrium analyses of carbonate rock samples using commercially available U and Th reagents and multi-collector ICP-MS

This study aims at developing a new analytical procedure for U–Th radioactive disequilibrium of carbonate rock samples. The procedure utilizes commercially available U and Th reagents as spikes for isotope dilution analysis with a multiple-collector inductively coupled mass spectrometer (MC-ICP-MS). Uranium and thorium in a carbonate sample were purified by Fe-coprecipitation, anion exchange resin, and U/TEVA resin. Isotopic compositions of purified spiked and unspiked U and Th were measured respectively for abundance and isotopic analyses. The correction of mass fractionation and the Daly/Faraday gain factor for Th measurements is carried out with a U standard solution. Accuracy of our method was confirmed by analyses of a coral sample that had been dated with thermal ionization mass spectrometry (TIMS). Our results indicate that U–Th disequilibrium studies are possible using easily available U and Th reagents as spikes.     

A new variable dispersion double-focusing plasma mass spectrometer with performance illustrated for Pb isotopes

A new generation multiple collector plasma source mass spectrometer (PSMS) produced by Nu Instruments Ltd is evaluated. The instrument has a double-focusing Nier–Johnson analyser with laminated magnet and a novel variable dispersion ion optical arrangement, enabling all masses to be located in the centre of the Faraday collectors of a fixed static array. mThe performance of the instrument has been assessed through the analysis of NBS-981 Pb using a Tl doping technique with Faraday collector efficiencies and amplifier gains determined independently. A second method of analysis involves comparison of interspersed standard and sample Pb measurements with effective gains for each collector determined from the standards. In both cases the repetition of Pb isotope measurement is competetive with the thermal ionization mass spectrometry (TIMS) double-spike method.     

Simultaneous analysis of uranium and plutonium using thermal ionization mass spectrometry

Simultaneous isotopic analysis of uranium and plutonium using thermal ionization mass spectrometer coupled to a multi-collector detection assembly with 9 Faraday cups has been reported earlier. Subsequently investigations have been carried out (1) to understand the applicability of correction methodologies available to account for the contribution of²³⁸Pu at²³⁸U and (2) to evaluate the effectiveness of these methodologies on the accuracy of²³⁵U/²³⁸U atom ratio being determined, particularly when samples containing different U/Pu atom ratios. Isotopic fractionation for both U and Pu in the simultaneous isotopic analysis has been compared with the results of the individual analysis of these elements. The different isotopic fractionation factors observed for U were attributed to different conditions of analysis. There was no significant difference in the isotopic fractionation patterns for Pu. The consideration to extend this method to actual samples from our observations on synthetic samples with diferent U/Pu atom ratios containing U and Pu isotopic reference standards is described.     

Mitigating dead‐time effects during multivariate analysis of ToF‐SIMS spectral images

ToF‐SIMS spectra are formed by bombarding a surface with a pulse of primary ions and detecting the resultant ionized surface species using a time‐of‐flight mass spectrometer. Typically, the detector is a time‐to‐digital converter. Once an ion is detected using such detectors, the detector becomes insensitive to the arrival of additional ions for a period termed as the (detector) dead‐time. Under commonly used ToF‐SIMS data acquisition conditions, the time interval over which ions arising from a single chemical species reach the detector is on the order of the detector dead‐time. Thus, only the first ion reaching the detector at any given mass is counted. The event registered by the data acquisition system, then, is the arrival of one or more ions at the detector. This behavior causes ToF‐SIMS data to violate, in the general case, the assumption of linear additivity that underlies many multivariate statistical analysis techniques. In this article, we show that high‐mass‐resolution ToF‐SIMS spectral‐image data follow a generalized linear model, and we propose a data transformation and scaling procedure that enables such data sets to be successfully analyzed using standard methods of multivariate image analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Direct determination of δ44/42Ca isotope ratio by ion chromatography/low‐resolution multicollector ICPMS

High‐precision on‐line procedure for measurement of calcium isotopic ratio by coupling ion chromatography to multicollector inductively coupled plasma mass spectrometry was developed. Calcium separation from the sample matrix was achieved on an ion chromatography column—IonPac CS16—ID 3 mm connected with CERS 500 2 mm suppressor and followed by multicollector inductively coupled plasma mass spectrometry calcium isotopic ratio determination. Dry plasma mode was used with Aridus II desolvation system. To sustained samples with high level of total dissolved salts as well as account capacity of applied analytical column, the method has been optimized regarding calcium isotope ratio measurements with low‐resolution mass spectrometry. Mass discrimination and instrument drift were corrected by sample‐standard bracketing method using the ⁴⁴Ca/⁴²Ca isotope ratio of SRM 915a as a standard. Good accuracy and reasonable precision of calcium isotope ratio (generally 0.20‰ [2SD]) were achieved, which are comparable to off‐line Ca separation and continuous measurement. The reproducibility of the proposed analytical procedure was verified by measuring the SRM 915a standard as a sample randomly over 3 months (n = 56). Applicability of the protocol was demonstrated for matrix‐rich natural water samples, coral samples, and bone standard reference materials.     

A new method for calibrating the current gain of 1013 Ω amplifiers in thermal ionization mass spectrometry

We report a new method for calibrating the current gain of 10¹³ Ω amplifiers in both positive and negative mode used in thermal ionisation mass spectrometry (TIMS). This method uses any isotopic standard or sample to calibrate the gain factor as long as it can produce a stable current signal. It is simpler and more flexible than that recommended by Thermo‐Fisher (the manufacture of the TIMS). In these analyses, the gains of five 10¹³ Ω amplifiers were assessed. The precision of gain factors was better than 100 ppm (2 RSD) in a day, and the long‐term reproducibility was better than 300 ppm (2 RSD) within 2 to 8 months. After a gain was calibrated, the ratio accuracy and precision in the positive mode for ⁸⁷Sr/⁸⁸Sr of NIST 987 Sr and ¹⁴³Nd/¹⁴⁴Nd of La Jolla Nd were 0.710242 ± 60 (2 SD, n = 14) and 0.511842 ± 10 (2 SD, n = 22), respectively, at intensities of ⁸⁸Sr 0.3 V and ¹⁴²Nd 0.4 V, while in the negative mode for ¹⁸⁷Os/¹⁸⁸Os of Merck Os was 0.120229 ± 34 (2 SD, n = 23) at an intensity of ¹⁸⁷OsO₃ 0.01 mV. In addition, a difference in the gain factors between the negative mode TIMS (NTIMS) and positive mode TIMS (PTIMS) has been recognized. The values of the gain factor for NTIMS and PTIMS show a deviation of 0.54% on the Triton and 0.31% on the Triton Plus TIMS in this study; therefore, gain calibration should be carried out on both NTIMS and PTIMS. Moreover, a bias of ~ 1.5 × 10⁻⁵ between H and L Faraday cups for the same 10¹³ Ω amplifier has been detected, hinting that the efficiency of different Faraday cups may affect the gain factors, which can be eliminated through the new method of “cross‐calibration” discribed in this study.     

Accurate measurement of uranium isotope ratios in soil samples using thermal ionization mass spectrometry equipped with a warp energy filter

A chemical and mass-spectrometric procedure for uranium isotopic analysis using a thermal ionisation mass spectrometer equipped with a Wide Aperture Retardation Potential energy filter has been developed and applied to uranium isotopic measurements for various soil samples. Soil samples were digested using a microwave digestor. Uranium was isolated from soil samples by the chemical separation procedure based on the use of anion-exchange resin and UTEVA extraction chromatography column. The isotope ratios were measured for two certified reference materials by using a VG Sector 54-30 thermal ionisation mass spectrometer in dynamic mode with Faraday cup and Daly ion counting system. Replicates of standard reference materials showed excellent analytical agreement with established values supporting the reliability and accuracy of the method. Precision of the ²³⁵U/²³⁸U ratio was achieved by a correction factor of 0.22% amu as a function of ion-beam intensity with sample loads of around 250?ng of U. The resulting reproducibility for standards and soil samples was better than 0.2% at two standard deviations (SD). Uranium isotopic compositions have been determined in several reference soil samples such as Buffalo river sediment, NIST 2704, river sediment SRM 4350b and ocean sediment NIST-4357 and a Chernobyl soil sample. There was a significant deviation from the natural uranium in comparison with Chernobyl soil samples.     

色谱/原子吸收联用系统中卧管式微火焰原子化离子化同步检测器的研究与应用

 介绍了一种新型的卧管式微火焰原子化离子化同步检测器 ,对其结构、工作原理及性能进行了研究。将其应用到色谱 /原子吸收联用系统中 ,实现了有机金属化合物以及与其共存的有机化合物的同步检测。有机金属化合物 (二乙基汞 )的原子吸收信号检出限为 2 5× 10 -11g/s;有机化合物 (苯 )的离子化信号检出限为 1 0× 10 -11g/s。     

The statistics of ToF‐SIMS data revisited and introduction of the empirical Poisson correction

Generation of time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) data involves two overarching processes: secondary ion production and secondary ion detection. The interpretation of ToF‐SIMS data is facilitated if the intensities of the as‐measured mass spectra are proportional to the abundances of the species under investigation. While secondary ion yield is normally taken to be a linear process, ion detection is not owing to detector dead‐time effects. Consequently, methods have been devised that attempt to linearize, or correct, data that are affected by the dead time. In this article, we review the statistics of ToF‐SIMS data generation and confirm a report in the literature that abundance estimates from so‐called Poisson corrections are biased. We show that these corrections are only unbiased asymptotically and that a rigorous probabilistic analysis can quantitatively account for the observed bias. Two sources of bias are identified, one having a statistical basis and one due to the form of the correction equation at high ion detection rates. Based on insights gained from this analysis, we propose a new correction equation, the empirical Poisson correction, which largely eliminates the statistical bias. The performance of the proposed correction is illustrated by reanalyzing 14 experimentally measured datasets that suffer from varying levels of dead‐time effects. Copyright © 2016 John Wiley & Sons, Ltd.     

Precise isotope-ratio measurements of lead species by capillary gas chromatography hyphenated to hexapole Multicollector ICP-MS

The precision and accuracy of lead isotope-ratio determination on a short transient signal has been assessed by coupling capillary gas chromatography to the Isoprobe (Micromass, UK), a single-focusing inductively coupled plasma mass spectrometer with multicollector detection. A T-piece connecting the GC transfer line to the torch enabled continuous aspiration of thallium solution for mass-bias correction. The volatile lead species PbEt4 was derivatized from NIST isotopic certified lead standard SRM 981 and different amounts of PbEt4 dissolved in iso-octane were injected into the GC. Chromatograms were recorded in multicollection mode by use of Faraday cups; seven isotopes (204Pb, 206Pb, 207Pb, 208Pb,     

Calculation methods for direct internal mass fractionation correction of spiked isotopic ratios from multi-collector mass spectrometric measurements

It is difficult to do internal mass fractionation corrections for isotope dilution analysis by thermal ionization mass spectrometry (TIMS) or multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), especially for MC-ICP-MS. In this study, calculation methods for direct internal fractionation correction of spiked isotope analysis by TIMS or MC-ICP-MS cycle by cycle for elements having at least two internal reference isotopic ratios are presented. For TIMS, direct internal mass fractionation correction calculation methods, based on both power and exponential laws, are derived; whereas for MC-ICP-MS, due to larger mass fractionation effects, only exponential law is considered. These calculation strategies can be applied for both static and multi-dynamic measurements. For multi-dynamic measurements, the isotope fractionation effect, gain and cup efficiency effects of different collectors, as well as ion beam fluctuation effects are all simultaneously eliminated. The calculation methods were verified by Sr isotopic analyses of spiked NBS987 standard solutions by TIMS and Hf isotopic analyses of spiked geological reference materials by MC-ICP-MS. In addition, precise and accurate calibrations of isotopic ratios of the spikes, based on the calculation methods, are discussed.     

Polytetrafluoroethylene physisorption‐assisted emulsification microextraction as a cleanup and preconcentration step in the gas chromatography determination of aliphatic hydrocarbons in marine sediment samples

For the first time, the application of polytetrafluoroethylene powder as an extractant phase collector or holder in liquid‐phase microextraction has been developed. For this purpose, the analytical performances of two different ways of applying polytetrafluoroethylene powder in microextraction methods including polytetrafluoroethylene physisorption‐assisted emulsification microextraction and dispersive liquid‐phase microextraction via polytetrafluoroethylene extractant phase holders have been compared for analysis of aliphatic hydrocarbons in aqueous phases. Under the same conditions, the former showed better extraction efficiencies over the latter and as a result, it was applied as preconcentration and cleanup step in the analysis of aliphatic hydrocarbons in sediment samples followed by gas chromatography analysis. The linearity of the polytetrafluoroethylene physisorption‐assisted emulsification microextraction method was obtained over a range of 3.7 and 2000 ng/g (R ² > 0.993). The relative standard deviations were less than 6.5% (n = 3). The limits of detection and quantification obtained by this method were 1.1–9.0 and 3.7–30 ng/g, respectively, indicating that satisfactory results were achieved by the procedure.     

Radioactivity levels in peloids used in main Cuban spas

In this work, an approach for determining both the outer dead layer thickness of the p-type coaxial HPGe detector and the inner dead layer thickness of the n-type coaxial HPGe detector was proposed by using two full energy peak area count ratios of a X-ray and a gamma ray emitted from the same radioisotope of ¹³⁷Cs. Monte Carlo calculations and experimental measurements were conducted to determine these dead layer thicknesses. The results showed that the outer dead layer thickness reached 0.57 ± 0.03 mm on 06 Jan 2017 after nearly 3 years of use for the p-type detector. The inner dead layer thickness reached 1.21 ± 0.24 mm on 01 Aug 2016 after more than 3 years of operation for the n-type detector. Simulation model with the modified dead layer thicknesses was used to estimate full energy peak efficiencies and gamma spectra from seven radioactive sources. The results were in good agreement with the corresponding experimental values in the gamma energy region of interest.     

Empirical equations for the temperature dependence of calcite-water oxygen isotope fractionation from 10 to 70°C

Although the temperature dependence of calcite‐water oxygen isotope fractionation seems to have been well established by numerous empirical, experimental and theoretical studies, it is still being discussed, especially due to the demand for increased accuracy of paleotemperature calculations. Experimentally determined equations are available and have been verified by theoretical calculations (considered as representative of isotopic equilibrium); however, many natural formations do not seem to follow these relationships implying either that existing fractionation equations should be revised, or that carbonate deposits are seriously affected by kinetic and solution chemistry effects, or late‐stage alterations. In order to test if existing fractionation‐temperature relationships can be used for natural deposits, we have studied calcite formations precipitated in various environments by means of stable isotope mass spectrometry: travertines (freshwater limestones) precipitating from hot and warm waters in open‐air or quasi‐closed environments, as well as cave deposits formed in closed systems. Physical and chemical parameters as well as oxygen isotope composition of water were monitored for all the investigated sites. Measuring precipitation temperatures along with oxygen isotope compositions of waters and calcites yielded empirical environment‐specific fractionation–temperature equations: [1] 1000 · lnα = 17599/T – 29.64 [for travertines with a temperature range of 30 to 70°C] and [2] 1000 · lnα = 17500/T – 29.89 [for cave deposits for the range 10 to 25°C]. Finally, based on the comparison of literature data and our results, the use of distinct calcite‐water oxygen isotopic fractionation relationships and application strategies to obtain the most reliable paleoclimate information are evaluated. Copyright © 2010 John Wiley & Sons, Ltd.     

2H/H] Isotope ratio analyses of [2H5]cholesterol using high-temperature conversion elemental analyser isotope-ratio mass spectrometry: determination of cholesterol absorption in normocholesterolemic volunteers

This paper validates the use of high-temperature conversion elemental analyser isotope-ratio mass spectrometry (TC-EA/IRMS) for measuring the [(2)H/H] enrichment of plasma [(2)H(5)]cholesterol. From a molecular point of view, the free cholesterol is initially separated from plasma by thin-layer chromatography (TLC) and then injected onto the TC-EA reactor which converts cholesterol molecules into CO and H(2) gases. The slope of the curve of the experimental mole percent excess (MPE((exp.))) versus MPE((theor.)) was very close to 1, demonstrating that no significant isotopic fractionation was observed during all processing of the samples (i.e., isolation of plasma free cholesterol by TLC and pyrolysis in the TC-EA reactor). Excellent linearity (r(2) = 0.9994, n = 4) of delta ( per thousand ) of [(2)H/H] isotopic measurements versus mole percent (MP) was assessed over the range 0 to 0.1 MP. The precision of the [(2)H/H] measurement, evaluated with two calibration points processed with TLC, was delta(2)H(V-SMOW) = -192.5 +/- 3.4 per thousand and delta(2)H(V-SMOW) = -136.9 +/- 2.9 per thousand. The standard deviations of the within-assay and between-assay repeatabilities of the analytical process, evaluated using the quality control (QC) of plasma samples, were 4.6 and 6.1 per thousand, respectively. Plant sterols are known to reduce cholesterol absorption and therefore were used as a positive control in a clinical study performed with normocholesterolemic volunteers. This present method produces biological results consistent with those already reported in the literature.     

The accuracy and precision of the advanced Poisson dead‐time correction and its importance for multivariate analysis of high mass resolution ToF‐SIMS data

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) data collected in single ion counting mode suffers from dead‐time effects that lead to potentially confusing artefacts when common multivariate analysis (MVA) methods are applied to the data. These artefacts can be eliminated by applying an advanced Poisson dead‐time correction that accounts for the signal intensity in the dead‐time window preceding each time channel. Because this correction is nonlinear, it changes the noise distribution in the data. In this work, the accuracy of this dead‐time correction and the noise characteristics of the corrected data have been analysed for spectra with small numbers of primary ion pulses. A simple but accurate equation for estimating the standard deviation in the advanced dead‐time corrected data has been developed. Based on these results, a scaling procedure to enable successful MVA of advanced dead‐time corrected ToF‐SIMS data has been developed. The improvements made possible by using the advanced dead‐time correction and our recommended scaling are presented for principal components analysis of a ToF‐SIMS image of aerosol particles on polytetrafluoroethylene. Recommendations are made for using the advanced dead time correction and scaling ToF‐SIMS data in order optimize the outcomes of MVA. Copyright © 2014 John Wiley & Sons, Ltd.     

Automated stir plate (bar) sorptive extraction coupled to high‐performance liquid chromatography for the determination of polycyclic aromatic hydrocarbons

Automated methods of PDMS/β‐CD/divinylbenzene‐coated stir plate sorptive extraction (SPSE) coupled to HPLC‐fluorescence detector were reported for the first time. Three automation modes, static SPSE, circular flow SPSE and continuous flow SPSE, were evaluated and critically compared with stir bar sorptive extraction by using six polycyclic aromatic hydrocarbons as model analytes. It was found that the operable sample volume for circular flow SPSE and continuous flow SPSE was larger than that for static SPSE. Under the same extraction conditions, continuous flow SPSE exhibited the highest extraction efficiencies in all automated modes and manual stir bar sorptive extraction for the target compounds. Compared with the manual operation (approximately 5–10 min), automated SPSE required a relatively short time (117–180 s) to finish sampling, washing and sample loading. Besides being labor‐saving and time‐saving, automated SPSE has other advantages, such as no time limit and non‐attended operation. The proposed continuous flow PDMS/β‐CD/divinylbenzene‐coated SPSE‐HPLC‐fluorescence detector was successfully applied to environmental water analysis.     

Simplified batch equilibration for D/H determination of non‐exchangeable hydrogen in solid organic material

Hydrogen isotopic analysis of organic materials has been widely applied in studies of paleoclimate, animal migration, forensics, food and flavor authentication, and the origin and diagenesis of organic matter. Hydrogen bound to carbon (C‐H) generally retains isotopic information about the water present during organic matter synthesis and associated biosynthetic fractionations, but hydrogen bound to other elements (O, S, or N) can readily exchange with atmospheric water vapor and reflects recent exposure to water or vapor. These two pools must be separated to obtain meaningful information from isotope ratios of organic materials. Previously published analytical methods either replace exchangeable H chemically or control its isotopic composition, usually by equilibration with water or waters of known isotopic composition. In addition, the fraction of H that is exchangeable can vary among samples and is itself of scientific interest. Here we report an improved and automated double‐equilibration approach. Samples are loaded in a 50‐position autosampler carousel in an air‐tight aluminum equilibration chamber. Water vapor of known isotopic composition is pumped through the chamber at 115°C for at least 6 h. After flushing with dry N₂ and being cooled, the carousel is rapidly transferred from the equilibration chamber to a He‐purged autosampler attached to a pyrolysis elemental analyzer connected to an isotope ratio mass spectrometer. By equilibrating two aliquots of each sample with two isotopically distinct waters, it is possible to calculate both (1) the D/H ratio of non‐exchangeable H, and (2) the fraction of H that is exchangeable. Relative to previous double‐equilibration techniques, this approach offers significant reductions in sample size and labor by allowing simultaneous equilibration of several tens of samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Evaluation and correction of isotope ratio inaccuracy on inductively coupled plasma time-of-flight mass spectrometry

Isotope ratio measurements are found to have systematic bias when using the analog detection mode on an inductively coupled plasma time-of-flight (TOF) mass spectrometer. This bias is dependent upon the value of the ratio, the intensity of the signal, and the gain of the electron multiplier tube. The error should not appear if ion counting is employed instead of analog detection, although analog detection with time-of-flight has other distinct advantages. The cause of this isotope ratio inaccuracy is rooted in disproportionate recording of the analog signal because of the need to filter out noise by blocking analog signals below a threshold voltage. This attenuates smaller signals to a greater degree than larger signals. This variable “detection efficiency” causes a larger systematic error in the isotopic ratio as the isotopic abundances become more disparate. Ratios close to unity are generally accurate within the precision of the measurement. The use of an increased gain on the detector leads to improved ratio accuracy, but at the cost of decreased detector lifetime. This research presents a method of analyzing solutions using natural, known isotopic ratios to produce an efficiency correction curve. The average error of several isotope ratios for a 500 ng/mL solution of various elements with ratios between 3.4 and 10 was found to be 6.5% without correction, 3.0% with increased detector gain, 1.1% with efficiency correction and 0.6% with both increased gain and efficiency correction.     

Fabrication of well‐aligned electrospun nanofibrous membrane based on fluorinated polyimide

We have fabricated novel nanofibrous fluorinated polyimide membranes on a specially designed collector, which is composed of conductive aluminum plates and glass insulator materials and can be removed from the apparatus, using an electrospinning method. We describe the structure and water flux properties of the nanofibrous fluorinated polyimide membranes. The electrospun nanofibers were deposited across the plates and uniaxially aligned to the collector. In addition, the multi‐layer stacked nanofibrous membranes, consisting of three‐dimensionally ordered nanopores, were produced. The pure water fluxes for the stacked membranes were measured, using a stirred dead‐end filtration cell, and were linearly decreased with an increasing deposition time, indicating that the nanopores formed in the nanofibrous membrane were further narrowed due to the regularly accumulated nanofibers. Copyright © 2009 John Wiley & Sons, Ltd.