Microcombustion of ng Amounts of Carbon in Non-Volatile Materials for isotope Ratio Evaluation

Abstract

A novel microcombustion technique for carbon isotopic analysis of nanogram amounts of carbon in non-volatile materials based on isotope ratio monitoring (irm) mass spectrometry is described. Liquid or solid samples placed in a quartz sleeve are combusted at 1000°C in a continuous stream of helium and oxygen. CO₂ removed from the carrier gas stream by cryogenic trapping is transferred onto a GC column. Following GC separation, the CO₂ is transferred via an open split to the ion source of a gas isotope ratio mass spectrometer. Reproducibility for samples >25 nmol carbon is <1‰. Problems associated with blanks from various sources and with reproducible deposition of small sample amounts led to variable accuracy, which was dependent on the compound class being analysed. Minimum sample size was in the range from 5 to 10 nmol carbon. Measurements of dissolved organic carbon (DOC) of groundwater from Germany yielded consistent values of δ¹³C = -28.8‰.     

应用显微激光拉曼光谱测定CO_2气体碳同位素值δ~(13)C的定量方法研究

单个流体包裹体同位素在研究岩矿古流体成因、矿床、油气和大地构造演化动力学等多个领域具有十分重要的意义,激光拉曼光谱是一项可以分析单个流体包裹体同位素的有效方法。本文提出应用显微激光拉曼光谱法来计算CO_2气体碳同位素值δ~(13)C。利用自行设计的装置将~(12)CO_2和~(13)CO_2按比例分别与N2混合,对混合气体样品进行显微激光拉曼测试分析后确定~(12)CO_2和~(13)CO_2的拉曼参数,这为用激光拉曼分析碳同位素值δ~(13)C奠定了理论基础。通过对不同比例的~(12)CO_2/~(13)CO_2人工合成CO_2包裹体样品和胜利油田CO_2天然气藏样品进行激光拉曼光谱分析,发现CO_2气体碳同位素摩尔分数比N_(13)/N_(12)与拉曼参数之间存在数学关系式,由此建立了根据碳同位素计算公式δ~(13)C=[(C_(13)/C_(12))_(样品)/(C_(13)/C_(12))_(标准)-1]×1 000‰,用激光拉曼分析获得的CO_2气体有关激光拉曼参数来计算δ~(13)C值的方法。按照该方法,应用显微激光拉曼光谱对胜利油田CO_2天然气藏样品分析计算其δ~(13)C值为-5.318‰,与用质谱仪分析测出的δ~(13)C值(-5.6‰)比较,其相对误差较小(≈5%),可以初步建立起应用显微激光拉曼光谱测定CO_2气体碳同位素值δ~(13)C的定量方法。     

Position-specific carbon isotope analysis of trichloroacetic acid by gas chromatography/isotope ratio mass spectrometry

Trichloroacetic acid (TCAA) is an important environmental contaminant present in soils, water and plants. A method for determining the carbon isotope signature of the trichloromethyl position in TCAA using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) was developed and tested with TCAA from different origins. Position-specific isotope analysis (PSIA) can provide direct information on the kinetic isotope effect for isotope substitution at a specific position in the molecule and/or help to distinguish different sources of a compound. The method is based on the degradation of TCAA into chloroform (CF) and CO? by thermal decarboxylation. Since thermal decarboxylation is associated with strong carbon isotope fractionation (ε = -34.6 ± 0.2‰) the reaction conditions were optimized to ensure full conversion. The combined isotope ratio of CF and CO? at the end of the reaction corresponded well to the isotope ratio of TCAA, confirming the reliability of the method. A method quantification limit (MQL) for TCAA of 18.6 μg/L was determined. Samples of TCAA produced by enzymatic and non-enzymatic chlorination of natural organic matter (NOM) and some industrially produced TCAA were used as exemplary sources. Significant different PSIA isotope ratios were observed between industrial TCAA and TCAA samples produced by chlorination of NOM. This highlights the potential of the method to study the origin and the fate of TCAA in the environment.     

Two-step synthesis of ethylene glycol-D6 via isotope exchange of glycolic acid

Tracers can be used to monitor emissions of leachate from landfills in order to detect hydrological pathways and to evaluate environmental pollution. We investigated the stable carbon isotope ratio (δ¹³C–Σ CO ₂) in dissolved inorganic carbon and tritium (³H) in water, in addition to the tracers of pollution commonly found in relatively high concentrations in leachate, such as chloride (Cl), organic matter (COD), nitrogen (total and NH₄–N), iron (Fe), electrical conductivity (EC) and pH. The sampling was performed at seven landfills in the south-eastern part of Norway during a period of 5 years. The objective was to evaluate the potential for tracing leachate in the environment with emphasis on groundwater pollution. By measuring the δ¹³C–Σ CO ₂ in leachates, groundwaters and surface waters, the influence of leachate can be identified. The value of δ¹³C–Σ CO ₂ varied from?5.5 to 25.9 ‰ in leachate, from?25.4 to 14.7 ‰ in groundwater and from?19.7 to?13.1 ‰ in creeks. A comparison of the carbon isotope ratio with COD, EC and the concentrations of total and NH ₄–N, Cl and Fe showed that δ¹³C–Σ CO ₂ is a good tracer for leachate due to higher sensitivity compared to other parameters. The mean concentrations of all the studied parameters were higher in the leachate samples; however, only the carbon isotope ratio showed significant differences between all the groups with strong and middle pollution and samples with low pollution, showing that it can be used as a convenient tracer for leachate in groundwater and surface water. The carbon isotope ratio showed strong correlation between nitrogen, EC and bicarbonate, but not with pH. Tritium was only sporadically found in measureable concentrations and is not considered as a suitable tracer at the sampled locations.     

A robust and fast method of sampling and analysis of δ13C of dissolved inorganic carbon in ground waters

The stable carbon isotopic composition of dissolved inorganic carbon (δ¹³C_DIC) is traditionally determined using either direct precipitation or gas evolution methods in conjunction with offline gas preparation and measurement in a dual-inlet isotope ratio mass spectrometer. A gas evolution method based on continuous-flow technology is described here, which is easy to use and robust. Water samples (100–1500 μl depending on the carbonate alkalinity) are injected into He-filled autosampler vials in the field and analysed on an automated continuous-flow gas preparation system interfaced to an isotope ratio mass spectrometer. Sample analysis time including online preparation is 10 min and overall precision is 0.1 ‰. This method is thus fast and can easily be automated for handling large sample batches.     

Determination of carbon isotope ratios of methanol and acetaldehyde in air samples by gas chromatography-isotope ratio mass spectrometry combined with headspace solid-phase microextraction

Isotopic signatures of atmospheric methanol and acetaldehyde have the potential to improve our ability to quantitatively assess their importance in atmospheric chemistry. However, isotopic measurements of atmospheric methanol and acetaldehyde and their individual source and sink processes have been limited. In this study, we examined gas chromatography-isotope ratio mass spectrometry combined with headspace solid-phase microextraction to measure the carbon isotope ratios of methanol and acetaldehyde in air samples. The method enabled us to determine carbon isotope ratios with a precision (1 standard deviation) of±0.6 ‰ for 20 ml of air sample containing more than 3 ppm of methanol and±0.7 ‰ for 20 ml of air sample containing more than 2 ppm of acetaldehyde. Moreover, the applicability of this method to determine isotope ratios of methanol and acetaldehyde emitted from detached plant leaves was demonstrated.     

Isotope-Ratio-Monitoring Liquid Chromatography Mass Spectrometry (IRM-LCMS): First Results from a Moving Wire Interface System

Abstract A Liquid Chromatography-Combustion (LC-C) Interface, based on a moving wire technique, has been built and tested. The LC effluent is deposited onto a transport wire, which carries the sample through solvent evaporation and combustion ovens. CO(2) from the combustion step is analysed in an isotope ratio mass spectrometer. Performance of the interface was tested by loop injections of sucrose and glucose into a liquid flow of methanol/water (80/20). Accuracy and precision of δ(13)C(PDB) < 1‰ was achieved for sample concentrations > 500 ng/ul (5μl loop), sufficient for studies at natural isotope ratios. In case of (13)C tracer applications the detection limit was determined to be about 20 pg carbon tracer (on wire).     

Stable isotopic analysis of pyrogenic organic matter in soils by liquid chromatography-isotope-ratio mass spectrometry of benzene polycarboxylic acids

Pyrogenic organic matter (PyOM), the incomplete combustion product of organic materials, is considered stable in soils and represents a potentially important terrestrial sink for atmospheric carbon dioxide. One well-established method of measuring PyOM in the environment is as benzene polycarboxylic acids (BPCAs), a compound-specific method, which allows both qualitative and quantitative estimation of PyOM. Until now, stable isotope measurement of PyOM carbon involved measurement of the trimethylsilyl (TMS) or methyl (Me) polycarboxylic acid derivatives by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). However, BPCA derivatives can contain as much as 150% derivative carbon, necessitating post-analysis correction for the accurate measurement of δ13C values, leading to increased measurement error. Here, we describe a method for δ13C isotope ratio measurement and quantification of BPCAs from soil-derived PyOM, based on ion-exchange chromatography (IEC-IRMS). The reproducibility of the δ13C measurement of individual BPCAs by IEC-IRMS was better than 0.35‰ (1σ). The δ13C-BPCA analysis of PyOM in soils, including at natural and artificially enriched 13C-abundance, produced accurate and precise δ13C measurements. Analysis of samples that differed in δ13C by as much as 900‰ revealed carryover of <1‰ between samples. The weighted sum of individual δ13C-BPCA measurements was correlated with previous isotopic measurements of whole PyOM, providing complementary information for bulk isotopic measurements. We discuss potential applications of δ13C-BPCA measurements, including the study of turnover rates of PyOM in soils and the partitioning of PyOM sources based on photosynthetic pathways.     

Role of water contamination within the GC column of a GasBench II peripheral on the reproducibility of 18O/16O ratios in water samples

The GasBench II peripheral along with MAT 253 combination provides a more sensitive platform for the determination of water isotope ratios. Here, we examined the role of adsorbed moisture within the gas chromatography (GC) column of the GasBench II on measurement uncertainties. The uncertainty in (18)O/(16)O ratio measurements is determined by several factors, including the presence of water in the GC. The contamination of GC with water originating from samples as water vapour over a longer timeframe is a critical factor in determining the reproducibility of (18)O/(16)O ratios in water samples. The shift in isotope ratios observed in the experiment under dry and wet conditions correlates strongly with the retention time of analyte CO(2), indicating the effect of accumulated moisture. Two possible methods to circumvent or minimise the effect of adsorbed water on isotope ratios are presented here. The proposed methodology includes either the regular baking of the GC column at a higher temperature (120?°C) after analysis of a batch of 32 sample entries or conducting the experiment at a low GC column temperature (22.5?°C). The effects of water contamination on long-term reproducibility of reference water, with and without baking protocol, have been described.     

A laser extraction/combustion technique for in situ delta(13)C analysis of organic and inorganic materials

A CO(2) laser extraction system is described for in situ delta(13)C analysis of organic and inorganic materials. Carbonaceous compounds volatilized by the laser are quantitatively converted to CO(2) gas by a combustion furnace mounted after the sample chamber. Gases produced by the laser and combustion processes are swept by helium carrier gas and separated by a packed gas chromatography column prior to their introduction to an isotope ratio monitoring mass spectrometer. A sample of lentil bean was analyzed at a spatial resolution of 200 μm and yielded delta(13)C values with precision of +/- 0.3 per thousand. The accuracy of delta(13)C measurements was better than +/- 0.5 per thousand from NBS 22 (mineral oil), USGS 24 (graphite), and IAEA CO-1 (calcium carbonate). Copyright 1999 John Wiley & Sons, Ltd.     

A robust and fast method of sampling and analysis of delta13C of dissolved inorganic carbon in ground waters

The stable carbon isotopic composition of dissolved inorganic carbon (delta13C(DIC)) is traditionally determined using either direct precipitation or gas evolution methods in conjunction with offline gas preparation and measurement in a dual-inlet isotope ratio mass spectrometer. A gas evolution method based on continuous-flow technology is described here, which is easy to use and robust. Water samples (100-1500 microl depending on the carbonate alkalinity) are injected into He-filled autosampler vials in the field and analysed on an automated continuous-flow gas preparation system interfaced to an isotope ratio mass spectrometer. Sample analysis time including online preparation is 10 min and overall precision is 0.1 per thousand. This method is thus fast and can easily be automated for handling large sample batches.     

Biodegradability screening of soil amendments through coupling of wavelength-scanned cavity ring-down spectroscopy to multiple dynamic chambers

A system was developed for the automatic measurements of 13CO? efflux to determine biodegradation of extra carbon amendments to soils. The system combines wavelength-scanned cavity ring down laser spectroscopy (WS-CRDS) with the open-dynamic chamber (ODC) method. The WS-CRDS instrument and a batch of 24 ODC are coupled via microprocessor-controlled valves. Determination of the biodegradation requires a known δ13C value and the applied mass of the carbon compounds, and the biodegradation is calculated based on the 13CO? mixing ratio (ppm) sampled from the headspace of the chambers. The WS-CRDS system provided accurate detection based on parallel samples of three standard gases (13CO? of 2, 11 and 22 ppm) that were measured simultaneously by isotope ratio mass spectrometry (linear regression R2 = 0.99). Repeated checking with the same standards showed that the WS-CRDS system showed no drift over seven months.The applicability of the ODC was checked against the closed static chamber (CSC) method using the rapid biodegradation of cane sugar-δ13C-labeled through C4 photosynthesis. There was no significant difference between the results from 7-min ODC and 120-min CSC measurements. Further, a test using samples of either cane sugar (C4) or beetroot sugar (C3) mixed into standard soil proved the target functionality of the system, which is to identify the biodegradation of carbon sources with significantly different isotopic signatures.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

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).     

Determination of (13)C/(12)C-Ratios in Rumen Produced Methane and CO(2) of Cows, Sheep and Camels

Abstract Naturally produced methane shows different δ(13)C-values with respect to its origin, e.g., geological or biological. Methane-production of ruminants is considered to be the dominant source from the animal kingdom. Isotopic values of rumen methane-given in literature-range between -80‰ and -50‰ and are related to feed composition and also sampling techniques. Keeping cows, camels and sheep under identical feed conditions and sampling rumen gases via implanted fistulae we compared δ(PDB) (13)C-values of methane and CO(2) between the species. Referring to mean values obtained from 4 or 5 samples at different times of 11 animals (n = 47) we calculated δ(PDB) (13)C-medians resulting in small but not significant differences within and significant differences between the species for CO(2) and methane. The δ(PDB) (13)C-differences between methane and CO(2) were statistically equal within and also between the species. Therefore a linear regression of methane values on CO(2) is appropriate and leads to: δ(PDB) (13)C(methane)‰ = 1,57 * δ(PDB) (13)C(CO(2))‰-47‰ with a correlation coefficient of r = 0,87.     

C and O stable isotopic signatures of fast-growing dripstones on alkaline substrates: reflection of growth mechanism, carbonate sources and environmental conditions

Secondary carbonate precipitates (dripstones) formed on concrete surfaces in four different environments--Mediterranean and continental open-space and indoor environments (inside a building and in a karstic cave)--were studied. The fabric of dripstones depends upon water supply, pH of mother solution and carbonate-resulting precipitation rate. Very low δ(13)C (average-28.2‰) and δ(18)O (average-18.4‰) values showed a strong positive correlation, typical for carbonate precipitated by rapid dissolution of CO(2) in a highly alkaline solution and consequent disequilibrium precipitation of CaCO(3). The main source of carbon is atmospheric or biogenic CO(2) in the poorly ventilated karstic cave, which is reflected in even lower δ(13)C values. Statistical analysis of δ(13)C and δ(18)O values of the four groups of samples showed that the governing factor of isotope fractionation is not the temperature, but rather the precipitation rate.     

Isotopic composition and concentration measurements of atmospheric CO2 with a diode laser making use of correlations between non-equivalent absorption cells

Correlations between a sample and a sealed reference cell of a tunable diode laser spectrometer for the measurement of the isotopic composition (δ ¹³C) and the concentration of atmospheric carbon dioxide in air have been investigated. Likely due to fluctuations of the laser emission profile, these correlations have been used to improve the performance of the instrument. In a comparison with isotope ratio mass spectrometer and gas chromatographic measurements, an accuracy of 0.15‰ for δ ¹³C and 0.05 ppmv for the CO₂ concentration is demonstrated for 40 s integration time. Long-term stability and field deployment of the instrument have been investigated during a few days measurement campaign in Paris.     

Analysis of polycyclic aromatic hydrocarbons extracted from air particulate matter using a temperature programmable injector coupled to GC–C–IRMS†

Compound specific isotopic analysis (CSIA) can provide information about the origin of analysed compounds – in this case, polycyclic aromatic hydrocarbons (PAHs). In the study, PAHs were extracted from three dust samples: winter and summer filter dust and tunnel dust. The measurement was performed using the method validated in our laboratory using pure, solid compounds and EPA 610 reference assortment.

CSIA required an appropriate clean-up method to avoid an unresolved complex in the gas chromatographic analysis usually found in the chromatography of PAHs. Extensive sample clean-up for this particular matrix was found to be necessary to obtain good gas chromatography–combustion–isotope ratio mass spectrometry analysis results. The sample purification method included two steps in which the sample is cleaned up and the aliphatic and aromatic hydrocarbons are separated.

The concentration of PAHs in the measured samples was low; so a large volume injection technique (100 μl) was applied. The δ_VPDB ¹³C was measured with a final uncertainty smaller than 1 ‰. Comparison of the δ_VPDB ¹³C signatures of PAHs extracted from different dust samples was feasible with this method and, doing so, significant differences were observed.     

Carbon isotope analysis of dissolved organic carbon in fresh and saline (NaCl) water via continuous flow cavity ring-down spectroscopy following wet chemical oxidation

This work examines the performance and limitations of a wet chemical oxidation carbon analyser interfaced with a cavity ring-down spectrometer (WCO-CRDS) in a continuous flow (CF) configuration for measuring δ¹³C of dissolved organic carbon (δ¹³C-DOC) in natural water samples. Low-chloride matrix (<5?g Cl/L) DOC solutions were analysed with as little as 2.5?mg C/L in a 9?mL aliquot with a precision of 0.5?‰. In high-chloride matrix (10–100?g Cl/L) DOC solutions, bias towards lighter δ¹³C-DOC was observed because of incomplete oxidation despite using high-concentration oxidant, extended reaction time, or post-wet chemical oxidation gas-phase combustion. However, through a combination of dilution, chloride removal, and increasing the oxidant:sample ratio, high-salinity samples with sufficient DOC (>22.5?µg C/aliquot) may be analysed. The WCO-CRDS approach requires more total carbon (µg C/aliquot) than conventional CF-isotope ratio mass spectrometer, but is nonetheless applicable to a wide range of DOC concentration and water types, including brackish water, produced water, and basinal brines.     

微型填充式气相色谱柱的制备（英文）北大核心CSCD

为了分离永久性气体及低碳轻化合物,基于MEMS技术,研究制备了一种微型填充式的气相色谱柱。为了增加色谱柱的长度以及深宽比,色谱柱的沟道制备采用了激光刻蚀技术,这种技术可以方便的在玻璃基底上刻蚀出深沟道,这是其他化学腐蚀技术无法比拟的。研制的色谱柱其沟道横截面为1.2mm(深度)×0.6mm(宽度),深宽比为2∶1。实验结果表明,这种微型填充柱,具有较大的样品容量,能很好的实现CO和SO_2的分离。