Dual Inlet System Research Articles

Revision of an open-split-based dual-inlet system for elemental and isotope ratio mass spectrometers with a focus on clumped-isotope measurements

Abstract. In this work, we present a revision of an open-split-based dual-inlet system for elemental and isotope ratio mass spectrometers (IRMSs), which was developed by the division of Climate and Environmental Physics of the University of Bern 2 decades ago. Besides discussing the corresponding improvements we show that with this inlet system (NIS-II, New Inlet System II) external precisions can be achieved that are high enough to perform measurements of multiply substituted isotopologues (clumped isotopes) on pure gases. For clumped-isotope ratios 35/32 and 36/32 of oxygen, we achieved standard deviations of 3.4×10-9 and 4.9×10-9, respectively, that we calculated from 60 interval means (20 s integration) of pure-oxygen gas measurements. Moreover, we report various performance tests and show that delta values of various air components can be measured with precisions of the order of tens of per meg and higher with the NIS-II. In addition, we demonstrate that our new open-split-based dual-inlet system allows us to measure some of these delta values with significantly higher precisions than an NIS-I (precursor of the NIS-II) and conventional changeover-valve-based dual-inlet systems (tests performed with two dual-inlet systems built by Elementar and Thermo Finnigan). Especially, our measurements point out that our inlet system provides reliable results at short idle times (20 s) and that the corresponding data do not need to be corrected for non-linearity. However, the sample consumption of our open-split-based dual-inlet system is several orders of magnitude higher than that of changeover-valve-based ones (0.33 sccm versus 0.005 sccm; standard cubic centimetres per minute). Due to the successful preliminary tests regarding measurements of clumped-isotope ratios, we will continue our work in this area to perform clumped-isotope studies according to common practices.

Isotope fractionation during capillary leaking in an isotope ratio mass spectrometer.

When isotope composition is measured in dual-inlet mode with an isotope ratio mass spectrometer (IRMS), reference gas may be gradually enriched in heavy isotopes due to preferential loss of light ones from the bellows over time. Quantifying the degree of isotopic enrichment of the reference gas is imperative for high-precision isotopic analysis (i.e. at per meg level). O2 and CO2 leaking experiments were performed with the dual-inlet system of an IRMS (Thermo Fisher® MAT 253 Plus). During each experiment, the drop of gas pressure in the bellows with time was recorded and isotope ratios of residual gas at various time intervals were analyzed. Isotopic enrichment of residual O2 gas could be as large as 1‰ for δ18 O when a large fraction (>75%) of initial gas was lost. The evolution of isotope compositions of the remaining gas can be well described by a pressure-dependent Rayleigh fractionation equation. When the pressure in the bellows is within 10-50 mBar, the isotope fractionation factor (α18 O) for O2 leaking ranges from 0.99911 to 0.99982 and the characteristic relationship of α17 O and α18 O is from 0.5123 to 0.5124. Isotope fractionation associated with capillary leaking from bellows is pressure-dependent. We recommend that the reference gas should be reloaded frequently, especially after a measurement with a low analyzing pressure for the analysis of small amounts of sample.

Stable carbon isotopic compositions and source apportionment of the carbonaceous components in PM2.5 in Taiyuan, China

To determine the stable carbon isotopic compositions (δ13C) and source apportionment of carbonaceous components in Taiyuan, PM2.5 samples were collected using medium flow samplers (TH-150C) during 4 months in 2014. The δ13C values of organic carbon (OC) and elemental carbon (EC) in PM2.5 were determined using an MAT-251 gas mass spectrometer with a dual inlet system. Moreover, δ13CEC values from industrial and domestic coal combustion were synchronously measured. In March, May, August, and December, the mean δ13COC values were −23.9 ± 0.9‰, −25.2 ± 0.2‰, −25.3 ± 0.6‰, and −22.9 ± 1.0‰, respectively; the corresponding δ13CEC values were −23.8 ± 0.8‰, −24.2 ± 0.5‰, −25.3 ± 0.4‰, and −23.8 ± 0.3‰; and the corresponding δ13CTC values were −23.8 ± 0.7‰, −24.8 ± 0.2‰, −25.3 ± 0.4‰, and −23.2 ± 0.6‰. Notable differences were observed in temporal distributions of stable carbon isotopic compositions of OC, EC, and total carbon (TC). The heavier δ13CEC values in December and March was caused by increased coal combustion and C4 plant burning during the heating season. The δ13CEC value was heavier than the δ13COC value in May, whereas the opposite was true in December. The δ13COC value may have been changed in atmospheric reactions during secondary organic aerosols formation in May and photochemical aging in December. There was almost no difference between δ13COC and δ13CEC in March and August. Source apportionment suggest that the EC sources in Taiyuan during the 4 months were different. EC in March and December was mainly due to fossil fuels (93.8%) and C4 plant burning (6.2%), EC in May was mainly affected by industrial coal combustion (50.0%) and vehicle exhaust (50.0%), and EC in August was the comprehensive result of fossil fuels (63.6%) and charcoal burning (36.4%). These results may enhance understanding of the sources of carbonaceous components in fine particles and may provide valuable data for environmental management.

Influences of Small Jet-to-Wall Spacings on Heat Transfer Characteristics and Flow-Field Entrainment Effects of Microscale Jets

Abstract Detailed heat transfer distributions of multiple microscaled tapered jets orthogonally impinging on the surface of a high-power density silicon wall is presented. The tapered jets issued from two different impingement setup are studied—(a) single circular nozzle and (b) dual circular nozzles. Jets are issued from the inlet(s) at four different Reynolds numbers {Re = 8000, 12,000, 16,000, 20,000}. The spacing between the tapered nozzle jets and the bare die silicon wall (z/d) is adjusted to be 4, 8, 12, and 16 jet nozzle diameters away from impinging influence. The impact of varying the nozzle to the silicon wall (z/d) standoff spacing up to 16 nozzle jet diameters and its effects on flow fields on the surface of the silicon, specifically the entrainment pattern on the silicon surface, is presented. Heat transfer characteristics of impinging jets on the hot silicon wall is investigated by means of large eddy simulations (LES) at a Reynolds of 20,000 on each of the four z/d spacing and compared against its equivalent Reynolds-averaged Navier–Stokes (RANS) cases. Highest heat transfer coefficients are obtained for the dual inlet system. A demarcation boundary region connecting all the microvortices between impinging jets is prominently visible at smaller z/d spacing—the region where the target silicon wall is within the sphere of influence of the potential core of the jet. This research focuses on the underlying physics of multiple tapered nozzles jet impingement issued from single and dual nozzles and its impact on turbulence, heat transfer distributions, entrainment, and other pertinent flow-field characteristics.

Performance of a Woodchip Bioreactor for the Treatment of Nitrate-Laden Agricultural Drainage Water in Northeastern Germany

Reactive barriers, such as denitrifying bioreactors, have been identified as a clean-up option for nutrient-laden agriculture runoff. Here we tested a 20 m long, 3.75 m wide and 2.2 m deep woodchip bioreactor receiving tile drainage water from a 5.2 ha field site, aiming at testing the hydraulic functioning of a dual-inlet system and quantifying its impact on nutrient loads (nitrogen, reactive phosphorus, organic carbon) in a region with a drainage season taking place in the hydrological winter (November to April). The hydraulic conditions in the dual-inlet bioreactor system developed differently than expected; asymmetric flow rates led to long average hydraulic retention times and a highly dispersed residence time distribution, which was revealed by a bromide tracer test. With a nitrate load reduction of 51 to 90% over three drainage seasons, the woodchip bioreactor proved at the same time to be very effective under the winter conditions of northeastern Germany. The bioreactor turned from an orthophosphate source in the first year of operation into an orthophosphate sink in the second and third year, which was not expected because of anoxic conditions (favorable for denitrification) prevailing within the woodchips. Besides an efficient nutrient retention, the woodchip bioreactor contributed to the total organic carbon load of receiving waters, which impairs the overall positive role of bioreactors within intensively agriculturally used landscapes. We consider this promising low-maintenance biotechnology particularly suitable for single drainage pipes with high discharge and high nitrate concentrations.

Ratio of naturally retained 15N to 13C in rat brain regions as a marker of brain function and activity

Our aim in the present study was to clarify the activity-dependent and function-associated retention of stable isotopes (SIs) in rat brain regions. We measured regional distributions of the natural stable isotopes 15N and 13C in brain using a mass spectrometer with a dual inlet system and a double collector for ratiometry, and compared them with distributions obtained from internal organs and skeletal muscle. Although levels of 15N and 13C were very high in brain regions of prenatal rats, and robustly decreased after birth, developmental changes in brain regions became obvious when the ratio of 15N to 13C (abbreviated as 15N/13C) in each brain region was compared. A high correlation was observed between free motor activity and 15N/13C in the hippocampus, cerebrum, and striatum. A significantly higher 15N/13C was also observed in the hippocampus and striatum of rats with higher intelligence, which was evaluated by radial maze learning. Furthermore, 15N/13C in brain regions of trained rats were significantly higher than those of untrained age-matched rats. Our study suggests that the 15N/13C in a specific brain region may reflect the physiological feature of the region. This ratio may hence be applicable as a maker for pathological research on undiagnosed brain diseases.

Improved validation for single particle ICP-MS analysis using a pneumatic nebulizer / microdroplet generator sample introduction system for multi-mode nanoparticle determination

This study reports on the development of a single-particle (sp) inductively coupled plasma mass spectrometry (ICP-MS) technique suitable for the multi-mode determination of nanoparticle (NP) metal mass fraction and number concentration. The described technique, which is based on a dual inlet system consisting of a pneumatic nebulizer (PN) and a microdroplet generator (MDG), allows for the sequential introduction of ionic metal calibrant solutions and nanoparticle suspensions via all combinations of the two inlets; thus allowing for a combination of three independent modes of analysis. A novel interface, assembled using standard analytical components (a demountable quartz ICP-MS torch, flexible non-conducting silicon tubing and various connectors), was used to interface the dual inlet system to an ICP-MS. The interface provided improved functionality, compared to a previous design. It is now possible to conveniently exchange and introduce standard solutions and samples via all inlet combinations, analyze them, and also wash the sample inlet systems while the whole setup is still connected to an operating ICP-MS. This setup provided seamless and robust operation in a total of three analysis modes, i.e. three ways to independently determine the metal mass fraction and NP number concentration. All three analyses modes could be carried out within a single analytical run lasting approximately 20 min. The unique feature of the described approach is that each analysis mode is based on a different calibration principle, thus constituting an independent way to determine metal mass fractions and nanoparticle number concentrations. Conducting the three independent state-of-the-art analysis, within a single analytical run, improves substantially the validation capabilities of sp-ICP-MS for NP analysis. To assess the technique’s analytical performance, Au, Ag and CeO2 nanoparticles were analyzed. The determined average diameters for Au (56.7 ± 1.5 nm), Ag (72.8 ± 3.4 nm) and CeO2 (69.0 ± 6.4 nm) NPs were in close agreement for all three modes of analysis, as well as with the values provided by suppliers’ for Au and Ag NPs (56.0 ± 0.5 for Au, 74.6 ± 3.8 nm for Ag). However, the determined average value for CeO2 was much higher than the expected 28.4 ± 10.4 nm, possibly due to NP agglomeration and the inability to detect NPs existing within the lower size range. The determined NP number concentrations, using analysis modes –I and –II, gave recoveries between 91 and 100% for the Au and Ag NP number concentrations. Whereas analysis mode –III showed a recovery of 70–88% for the same materials. Because of the polydispersity, the small size and polyhedral shape of the CeO2 NPs it was not possible to make NP number concentration comparisons for this material.

Combined high-precision ∆48 and ∆47 analysis of carbonates

High-precision analysis of the excess abundance (relative to the stochastic distribution) of mass 48 isotopologues in CO2 evolved from acid digestion of carbonates (∆48) has not been possible until recently due to the relatively low natural abundance of 18O. Here we show that the 253 Plus™ gas source mass spectrometer equipped with Faraday cups and 1013 Ω resistors can perform combined ∆47 and ∆48 analyses on carbonates with external reproducibilities (1SD) of 0.010 ‰ and 0.030 ‰, respectively.~10 mg aliquots of five carbonate reference materials (ETH 1, ETH 2, ETH 3, ETH 4, and Carrara) are digested with phosphoric acid at 90 °C using a common acid bath. The evolved CO2 is purified using an automated gas preparation system (including cryotraps and a GC) and analyzed for its ∆47 and ∆48 compositions using the dual inlet system of a 253 Plus™ gas source mass spectrometer. Raw ∆47 and ∆48 values are finally normalized to the Carbon Dioxide Equilibrium Scale (CDES).In ∆47, CDES 90°Cvs. ∆48, CDES 90°C space, calcite reference materials Carrara, ETH 3 and ETH 4 agree with the equilibrium curve for calcite after adding semi-empirically determined 90 °C acid fractionation factors of 0.196 ‰ (for ∆47) and 0.136 ‰ (for ∆48) to theoretical ∆63 and ∆64 data. Agreement between measured and theoretically expected ∆48, CDES 90°C highlights the accuracy of our high-precision clumped isotope analytical setup. Combined analysis of the abundances of mass 47 and mass 48 isotopologues in CO2 evolved from acid digestion of natural carbonates has excellent potential for the determination of accurate and highly precise paleotemperatures as well as for the identification of rate-limiting kinetic processes involved in biomineralization. A formation temperature of 15(±2) °C is obtained on the 95 % confidence level for the Upper Cretaceous chalk sample ETH 3.

A new negative and positive gas ion source for isotope ratio mass spectrometry.

The goal of this research was to construct an effective gas ion source for isotope ratio mass spectrometry, which generates sufficiently strong and stable ion beams for multiple isotope ratio analysis of sulfur and oxygen from readily available gases such as SO2 , CO2 , CO, O2 and chlorine from CH3 Cl gas. By means of a 60° sector mass spectrometer equipped with a new type of sensitive ion source and with a dual-inlet system and triple collector assembly, we have measured 34 S/32 S and challenging 36 S/32 S isotope ratios using positive sulfur ions generated from SO2 gas. The new ion source differs from the Nier-type ones by the electron beam being replaced with a tungsten filament. The obtained isotope signals of 32 S+ , 34 S+ and 36 S+ were from 1 to 5V (depending on the pressure of admitted gas) on high-ohm resistors of 200MΩ, 5 GΩ and 500 GΩ, respectively. The variable 33 S peak was not recorded as useful due to interference from H32 S+ ions. Although the ionizing electrons in the new ion source have significant energy dispersion the obtained peak profiles are flat-topped and they lead to good resolving power for the mass spectrometer (M/∆M≈100). The achieved precision of δ34 S and δ36 S determination was better than ±0.01 and ±0.1‰, respectively. The determination of 37 Cl/35 Cl in a volatile organic compound CH2 Cl2 was easily achieved on Cl- negative ions with a precision of ±0.005‰. The new ion source has great potential in the quantitative analysis of gases on positive ion mass spectra as well as, in the case of gases with high electron affinity such as CH3 Cl, CH3 Br, SF6 , SiF4 , on negative ones. It usefulness was demonstrated on an example of multiple sulfur isotope analysis and 37 Cl/35 Cl ratio determination with great precision. A negative ion source of this type will probably be useful in a more complicated instruments used in SIMS or AMS. Copyright © 2017 John Wiley & Sons, Ltd.

Isotopic and geochemical characterization of invader tilapia fishes from water bodies of West Bengal and Karnataka, India.

The otoliths (N = 12) of freshwater invasive species tilapia (Tilapia mossambicus) collected from two water bodies located at Kolkata and Bangalore, India, were analyzed for stable isotopes (δ18O, δ14C) and major and trace elements in order to assess the suitability of using otoliths as a tracer of aquatic environmental changes. The stable isotope analysis was done using the dual inlet system of a Finnigan-MAT 253 isotope ratio mass spectrometer (Thermo-Fisher, Bremen, Germany). Concentrations of major and trace elements were determined using a Thermo X-Series II quadrupole mass spectrometer. The stable isotope composition in tilapia otolith samples from Bangalore and Kolkata water bodies are quite good agreeing with that of the respective lake/pond and rain water. Elemental composition revealed in a pattern of Ca>Fe>Na>Sr>K>Ba>Cr>Mg>As>Mn>Zn>Co>Cu>Cd>Pb. The otoliths from Kolkata pond water are more enriched in Ba, Zn, Pb, Mn, Se, Cu, Zn, Cd, and Ni whereas Cr and As were found to be higher in otolith samples from Bangalore lake. The enrichment factor (EF) values of Cr were higher for both the sampling location in comparison with other metals, although all the studied metals exhibited EF values>1. The PCA shows clustering of metals in the otolith which are related either with the metabolic and physiological attributes or waterborne source. The study demonstrated the potential of stable isotope techniques to distinguish otolith specimens from varied climatic zone, while elemental composition recorded the quality of water at both the locations. The role of climate driving the quality of water can be understood by detailed and continuous monitoring of otolith specimens in the future. Future method allows reconstruction of climate and water quality from old specimens from field exposures or museum collection.

The prospective development of Climate and Environmental Research Laboratory of AARI, Roshydromet, after gaining the grant of Russian Science Foundation

In November 2010 a new research unit was inaugurated in Arctic and Antarctic Research Institute (St. Petersburg) – Climate and Environmental Research Laboratory (CERL) – that became the first lab in Russia dedicated to the complex studies of ice cores, paleoclimate and subglacial environments in Antarctica. The total investments to construct the laboratory were 28.8 million rubles, provided by Roshydromet and AARI in frames of implementing the program of International Polar Year. The total area of the laboratory is about 300 m² that includes mass-spectrometric and gas analyses labs, cold chambers and utility rooms. The CERL’s equipment comprises laser stable water isotope analyzer Picarro L2120-i, IR mass-spectrometer Delta V Plus, system of gas extraction from ice, facilities for ice petrographic observations, for ice core treatment and storage. Before 2014 CERL was the head unit in the project “Complex studies of Lake Vostok and glaciological investigations of Antarctica” of the sub-program “Antarctica” of the FTP “World Ocean”. Now CERL is the leading organization in International Associated Laboratory “Ice archives of climatic and environmental data” that combines 4 French and 5 Russian scientific research groups. In 2014 the specialists of CERL won a grant of Russian Science Foundation for fundamental scientific works implemented by operating research laboratories. Project 14-27-00030 “Evolution of climate, glaciation and subglacial environments of Antarctica from the deep ice core and Lake Vostok water sample studies” (2014–2016) is intended to refine the reconstruction of Antarctic climate history over the past 400,000 years using the newly developed geochemical methods of ice core studies. Another goal is to develop the approaches to study the hydrological parameters of subglacial Lake Vostok using the samples of lake ice and water. The funding to be received through the grant (58.5 million rubles) will be mainly spent to develop the analytical infrastructure of the laboratory. In particular, we plan to equip the “Delta” with the dual inlet system and “Gas Bench II” device, as well as to purchase the new generation of laser isotope analyzer, Picarro L2140-i. This will allow us to measure precisely the concentrations of deuterium, oxygen 18 and 17 in water, snow and ice samples, to define the О₂/N₂ ratio in the gas probes, as well as to develop new methods of ice core analyses.

Morphodynamics of an anthropogenically altered dual-inlet system: John's Pass and Blind Pass, west-central Florida, USA

The morphodynamics of the John's Pass–Blind Pass dual inlet system were investigated based on hydrodynamic and morphology measurements, and numerical modeling. The co-existence of the dual inlets is realized by the dominance of mixed-energy John's Pass in terms of tidal prism and size of the ebb delta and the artificial maintenance of the wave-dominated migratory Blind Pass. Due to the secondary role of Blind Pass, the aggressive anthropogenic activities there do not seem to have a significant influence on the morphodynamics of John's Pass. On the other hand, the opening (in 1848) and subsequent evolution of John's Pass had substantial influence on Blind Pass, causing it to migrate rapidly to the south. In addition, anthropogenic activities had much more influence on the morphodynamics of the secondary Blind Pass than that of the dominating John's Pass.Results from numerical modeling provide a semi-quantitative understanding of the hydrodynamics and morphodynamics of John's Pass and Blind Pass in association with cold front passages, which have substantial influences on inlet morphology. Two large eddies are modeled from the interactions between the southward longshore current and John's Pass ebb and flood flow, respectively. These eddies are closely related to the morphodynamics of the channel margin linear bar and longshore transport divergence at the downdrift side. Both are key features of a mixed-energy inlet. The shallow water and wave-breaking-induced longshore current and elevated sediment suspension along the ebb delta terminal lobe provide the pathway for sediment bypassing. The morphodynamics of Blind Pass are dominated by wave forcing. The weak ebb jet is not capable of forming a sizable ebb delta and tends to be deflected by the strong longshore current, causing elevated longshore transport along the downdrift beach. The 90-degree turn of the inlet, which is common for wave-dominated migratory inlets, results in weak ebb flushing along the updrift (north) side of the inlet, and is responsible for the alongshore migration of the inlet before the artificial stabilization and sedimentation along the northern side of the inlet following stabilization.

Modeling Regional-Scale Sediment Transport and Medium-Term Morphology Change at a Dual-Inlet System Examined with the Coastal Modeling System (CMS): A Case Study at Johns Pass and Blind Pass, West-Central Florida

The Coastal Modeling System (CMS), developed by the US Army Engineer Research and Development Center's (ERDC) Coastal Inlets Research Program (CIRP), is applied to model morphology change at a dual-inlet system, the Johns Pass and Blind Pass system in West-Central Florida. The CMS combines computation of current, wave, and sediment transport, leading to the prediction of morphology change at tidal inlets and the surrounding beaches. Medium-term CMS runs, with simulated times of 1.2 to 1.6 years, were completed and compared with extensive field data. Stronger tidal flow through the dominating Johns Pass and weaker flow through the secondary Blind Pass were calculated, indicating that the model reproduced an essential aspect of this interactive two-inlet system. The complicated wave refraction and breaking over the ebb tidal deltas and along the adjacent shorelines were accurately modeled, leading to a realistic representation of the wave-current interaction. Wave-breaking induced elevated sediment suspension and transport were described by the model. The predicted morphology change agreed well with field data. The CMS captured several key spatial trends of morphology change, e.g., erosion along the downdrift beach and accretion at the attachment point. The computed 32,000 m3/yr sedimentation volume in the dredge pit at the updrift side of Blind Pass matched the measured value of 35,000 m3/yr with a similar spatial distribution pattern, suggesting that the calculated net longshore sediment transport rates are accurate. The computed sedimentation rate of 60,000 m3/yr at a designed dredge pit on Johns Pass ebb-delta agrees with the generally accepted gross longshore transport rate. Rapid and large morphology change in response to high wave-energy events is predicted and is consistent with field observations.

New isotope ratio mass spectrometric method of precise δ37Cl determinations

The most precise method of chlorine isotope analysis described to date is based on the isotope ratio mass spectrometry (IRMS) of chlorine quantitatively converted into chloromethane, CH(3)Cl. This gas can be produced from several chlorine-containing compounds and analyzed by IRMS. However, the mass spectrum of chloromethane is rather complicated and the ratio of the most abundant ions (mass-52/mass-50) differs from the (37)Cl/(35)Cl isotope ratio. This difference becomes significant when the delta37 Cl exceeds 10 per thousand. Moreover, the electron ionization source yields approximately 80% of all the ionic species at the useful masses 50 and 52. To overcome these drawbacks, we have devised a negative ion mass spectrometer which retains all the best features of IRMS, including a dual-inlet system with changeover valve, dual collector assembly and CH(3)Cl gas as analyte. In the modified ion source we have replaced the ionization chamber with an electron beam by a metal tube with a hot metal filament inside it. Within this tube the (35)Cl(-) and (37)Cl(-) ions are produced with an efficiency dependent on the filament material and its temperature. No other ionic species were found in the mass spectrum except of traces at masses 26 and 28 at ppm levels, probably due to the formation of CN(-) and CO(-). The minimal amount of Cl used in our method is of the order of 5 micromol (3 mg AgCl) and the precision is better than 0.005 per thousand (1sigma).

Cross contamination in dual inlet isotope ratio mass spectrometers

Since the early days of geochemical isotope ratio mass spectrometry there has always been the problem of cross contamination, i.e. the contamination of the sample gas with traces of reference gas (and vice versa) in a dual inlet system and the analyzer itself. This was attributable to valve leakages and could be corrected for. In modern leak-free machines this problem still influences the measurements by scale contraction. It limits the interlaboratory comparability to values unacceptable for, e.g. global carbon cycle investigations on atmospheric δ 13CO 2, with the need to integrate global datasets at a 0.01‰ precision level. No matter what the reason of apparent cross contamination (physical leakage, low pump efficiency, gas–wall interactions), we present a method to measure the actual cross contamination as well as algorithms to correct for it. By using isotopically enriched sample gas the effect on the reference gas is directly shown. Especially for biomedical applications, employing highly enriched materials, the nonlinear correction has to be applied. A long-time record of two machines shows the influence of vacuum breakage and the inlet system setup. We present a survey of cross contamination in some of the frequently used machines. The relatively poor raw results of two recent interlaboratory comparison experiments are explained in terms of cross contamination. Whereas the linear two-point normalization procedure considered by itself may be appropriate for some routine applications at natural isotope abundances, it always relies on relative δ values of two reference materials. There is an urgent need to establish absolute values for all scale-determining reference materials. We recommend the use of cross contamination measurements to at least determine the isotopic composition of all normalization materials as long as absolute measurements are not available. In principle, the cross contamination measurements should be used as a diagnostic tool on a regular basis.

European interlaboratory comparison of breath13CO2 analysis

The BIOMED I programme Stable Isotopes in Gastroenterology and Nutrition (SIGN) has focused upon evaluation and standardisation of stable isotope breath tests using 13C labelled substrates. The programme dealt with...

Profiles of transitions in Ar VIII

The gas-liner pinch has been developed into a well-diagnosed plasma device most suitable for line shape studies of multiply ionized atoms. One special feature is the dual gas inlet system, which allows one to seed the final dense plasma column along its axis with test gas ions of interest at variable concentration. Temperatures and densities of electrons, main and test gas ions are measured by collective Thomson scattering employing a ruby laser. Reliable comparisons with theoretical line profiles are thus possible stimulating refined calculations. Furthermore, macroscopic instabilities can be induced by high test gas concentrations offering the possibility of line shape studies under such conditions. In this report line shape measurements of two Ar VIII lines embedded in dense hydrogen plasmas are presented at stable plasma conditions and compared with theoretical calculations.

Use of nitrous oxide as a purge gas for automated nitrogen isotope analysis by the Rittenberg technique

An apparatus that operates with an isotope-ratio mass spectrometer to automatically perform nitrogen isotope analyses by the Rittenberg technique was modified to permit the use of nitrous oxide (N2O) instead of Freon (CCl2F2 or CHClF2) for the purging of air prior to hypobromite oxidation of ammonium-N to N2 in a plastic microplate. Analytical performance was unaffected by the modifications. Up to 768 samples can be processed in a single loading, at a rate of 6 to 12 samples/h. Within the range of 0.2 to 20 atom % 15N, isotope-ratio analyses of 50 to 200 μg of N using the automated Rittenberg apparatus (ARA) with a double-collector mass spectrometer were accurate to within 0.7%, as compared to manual Rittenberg analyses of 1 mg of N using the same mass spectrometer with a dual-inlet system. Automated analyses of 20μg of N were accurate to within 2%, and automated analyses of 10 μg of N were accurate to within 7%. The relative standard deviation for measurements at the natural abundance level (10 analyses, 20-200 μg of N) was < 0.04 %.

Dual-Inlet Chemical Amplifier for Atmospheric Peroxy Radical Measurements

The state-of-the-art of peroxy radical measurements using the technique of chemical amplification has matured in recent years. The NCAR chemical amplifier has been improved over previous versions by employing a dual-inlet system that allows more rapid switching between measurement and background modes. Further improvement is realized by the use of two NO(2) detectors. The dual-inlet chemical amplifier (DICHAMP) employs two identical glass inlet reactor-NO(2) detector combinations, one of which is operated in the background, while the other operates in the radical measurement mode. This instrument is less sensitive to fluctuations in ambient ozone than the single-channel version because of the continuous monitoring of the background and background plus radical signals. The single-inlet, dual-inlet with single-detector, and DICHAMP instruments are compared through theoretical calculations of the effect of noise at a given frequency and amplitude on retrieved radical levels. Laboratory experiments were conducted to support the theoretical results. Ambient radical concentrations were determined using these configurations to evaluate the performance under actual measurement conditions.

New Methods for Fully Automated Isotope Ratio Determination from Hydrogen at the Natural Abundance Level

Abstract A variety of methods for measurement of (2)H/(1)H from H(2) are evaluated for their ability to be fully automated and for applicability to automated isotopic analysis of water and organic compounds. Equilibration of water with H(2) gas with the aid of a platinum catalyst has been commercialized into a fully automated sample preparation device. A second and newer technique, involving injecting water, methane, or other volatile organic compounds onto hot chromium in a reactor attached to the dual inlet system of a gas isotope ratio mass spectrometer, can be integrated with a conventional GC-autosampler to allow automated analysis of a variety of substrates. Both techniques result in precisions around 1‰ (δ notation) on the VSMOW scale, and are fast and accurate, and with appropriate mass spectrometers require only negligible scaling for the SLAP/VSMOW difference. Several experimental methods which show considerable promise employ "isotope ratio monitoring" (irm) inlet systems, in which a carrier gas is used for transport of H(2) to the mass spectrometer. Any such method has to address the problem of He ions corrupting the measurement of the H(2) ions. One such approach uses a heated palladium membrane for selective introduction of H(2) into the mass spectrometer, and a second involves modifications to the ion optics to control the stray helium ions. Both approaches have significant limitations that must be overcome before irm techniques can be used in routine applications, in particular for measuring hydrogen isotopes from GC effluents (irm-GCMS).