Sealed Tube Combustion Research Articles

Nitrogen Mass Fraction and Stable Isotope Ratios for Fourteen Geological Reference Materials: Evaluating the Applicability of Elemental Analyser Versus Sealed Tube Combustion Methods

Thirteen commercially available silicate reference materials (RM) and one in‐house reference material, eleven of which have no previously published values, were analysed for nitrogen mass fraction and isotopic ratios with an Elemental Analyser (EA), and a Sealed Tube Combustion line, coupled to a continuous flow isotope ratio mass spectrometer (IRMS). These materials ranged from < 10 μg g−1 to 1% m/m nitrogen mass fractions and δ15N of −0.5 to +19.8‰. Existing nitrogen RM BHVO‐2, MS#5 and SGR‐1b were used to assess the accuracy of the data from the sealed tube combustion line, which was found to be in good agreement with existing published values. In contrast, the EA‐IRMS failed to fully liberate nitrogen from all silicate rocks and minerals (achieving a mean of 44 ± 10% nitrogen yield) resulting in kinetic fractionation of isotope values by −1.4‰ on average. Therefore, sealed tube combustion is better suited for analyses of silicate‐bound nitrogen. The EA worked reliably for organic samples, but care should be taken when using the EA for silicate nitrogen research. Moving forward, it is recommended that BHVO‐2, Biotite‐Fe, FK‐N and UB‐N be used as quality control materials as they appear to be most reproducible in terms of nitrogen mass fraction (relative error < 10%, 1s), and isotopic composition (< 0.6‰, 1s).

Sealed Tube Combustion Method with MnO2 for AMS 14C Measurement

ABSTRACTAn effective sealed tube combustion method was designed with an MnO2 oxidant for accelerator mass spectrometry radiocarbon (AMS 14C) measurements. Different types of materials (oxalic acid, cellulose, sucrose, wood, collagen, graphite, and humic acid) were used to test the method. A normal borosilicate glass tube was used instead of quartz and the combustion was done at 550ºC. The yield of the combustion is above 98% even in the case of the less combustible material such as graphite. The MnO2 reagent does not introduce detectable carbon contamination. The typical background is 0.29±0.20 pMC in the case of 200 µg carbon, measured as solid graphite target. With direct measurement of the CO2 by gas ion source AMS, the method is applicable up to 50 µg of carbon with an acceptable (~1 pMC) 14C background. A new type of tube cracker was developed for a quick chipless method of tube cracking and sample changing. In this way, the gas handling process takes only 5–6 min/sample.

Evaluation of an automated EA-IRMS method for total carbon analysis of atmospheric aerosol at HEKAL

Comprehensive atmospheric studies have demonstrated that carbonaceous particles are one of the main components of atmospheric aerosols over Europe. The aim of our study was to establish an automated elemental analyser interfaced to a stable isotope mass spectrometer (EA-IRMS) method at the Hertelendi Laboratory of Environmental Studies (HEKAL), as a suitable method of quantification of total carbon mass in individual PM2.5 aerosol samples. Total carbon (TC) mass and simultaneous stable isotopic ratios were determined for both test standard and genuine aerosol samples. Finally, the results were compared to the ones obtained independently by an alternative sealed tube combustion method developed previously at HEKAL. The TC recovery tests of standard material prepared by the sealed tube method confirmed at least a carbon recovery yield of 92% for a broad range of carbon mass (100–2000 μg). The stable isotopic results confirmed that sealed tube method is reproducible and suitable to be used as a reference to verify our new EA-IRMS method. The EA-IRMS TC measurements of genuine aerosols gave on average 3% higher carbon recovery yield, relative to the uncorrected results of the sealed tube method. The comparison of the stable isotopic results by the two methods for aerosols also showed minimal differences. Consequently, the possibility of simultaneous TC and stable isotopic analyses makes the EA-IRMS method a very attractive alternative for continuous measurement of aerosols, with an accuracy and reliability similar to other commercial devices.

Rapid 14C Analysis of Dissolved Organic Carbon in Non-Saline Waters

AbstractThe radiocarbon content of dissolved organic carbon (DOC) in rivers, lakes, and other non-saline waters can provide valuable information on carbon cycling dynamics in the environment. DOC is typically prepared for 14C analysis by accelerator mass spectrometry (AMS) either by ultraviolet (UV) oxidation or by freeze-drying and sealed tube combustion. We present here a new method for the rapid analysis of 14C of DOC using wet chemical oxidation (WCO) and automated headspace sampling of CO2. The approach is an adaption of recently developed methods using aqueous persulfate oxidant to determine the δ13C of DOC in non-saline water samples and the 14C content of volatile organic acids. One advantage of the current method over UV oxidation is higher throughput: 22 samples and 10 processing standards can be prepared in one day and analyzed in a second day, allowing a full suite of 14C processing standards and blanks to be run in conjunction with samples. A second advantage is that there is less potential for cross-contamination between samples.

Improvement of analytical method for chlorine dual‐inlet isotope ratio mass spectrometry of organochlorines

The development of compound-specific chlorine isotope analysis (Cl-CSIA) is hindered by the lack of international organochlorine reference materials with isotopic compositions expressed in the δ(37) Cl notation. Thus, a reliable off-line analytical method is needed, allowing direct comparison of the δ(37) Cl values of molecularly different organic compounds with that of ocean-water chloride, to refer measurement results to a Standard Mean Ocean Chloride (SMOC) scale. The analytical method included sealed-tube combustion of organochlorines, precipitation and subsequent conversion of formed inorganic chlorides into methyl chloride (CH3 Cl) for the determination of δ(37) Cl values by Dual-Inlet Isotope Ratio Mass Spectrometry (DI-IRMS). A sample preparation step most sensitive to the sample size - dissolution of the inorganic copper chlorides formed by combustion of organochlorines - was identified. Recovery of 94 ± 5% of chlorine was reached by applying determined optimal conditions for the dissolution, implying good external precision of δ(37) Cl values (-0.18 ± 0.03‰, 1σ, n = 3). Validation of the optimized method by the analysis of the produced and initial CH3 Cl samples with known δ(37) Cl values vs SMOC resulted in a difference of 0.11 ± 0.04‰ (1σ, n = 3), confirming the external precision and accuracy of the entire method. The efficiency of the sample preparation method for CH3 Cl-DI-IRMS analysis is independent both of the chemical structure of the chlorinated compound and of the amount of chlorine in the sample. This method has the potential to be applied to a broad range of chlorinated organic compounds, e.g. reference material for the calibration of methods for Cl-CSIA against SMOC.

Determination of carbon isotopic measurement conditions for ceramide in skin using gas chromatography-combustion-isotope ratio mass spectrometry.

The ceramide (Cer) content of skin and glucosylceramide (GlcCer) intake affect skin moisture conditions, but their mutual relation in skin remains unclear. For clarification of that mutual relation, carbon stable isotopes ((12)C and (13)C) are useful as a tracer. However, carbon isotopic measurement has not been applied to the study of clarifying their skin moisturizing effects. Therefore, we used gas chromatography / combustion / isotope ratio mass spectrometry (GC-C-IRMS) to ascertain the appropriate conditions for carbon isotopic measurements using synthesized Cer (SCer) in substitution for very low concentrations of Cer in skin. SCer was derivatized to trimethylsilylated SCer (TMS-SCer) quantitatively using N-trimethylsilylimidazole (TMSI) depending on the amount of SCer. The derivatization rates were 75-85%. Excess TMSI was removed using three cycles of hexane-water distribution. Under these conditions, carbon isotopic measurements of TMS-SCer conducted using GC-C-IRMS showed high repeatability and good inter-day variation (S.D. < 0.3‰). The carbon stable isotope ratio value (δ(13)C) of SCer calculated using a mass balance equation was compared with δ(13)C of underivatized SCer, which was regarded as the actual δ(13)C of SCer obtained using sealed tube combustion method. The difference between the calculated δ(13)C of SCer and δ(13)C of the underivatized SCer depended on the TMSI reagent supplier and on the number of hydroxyl groups to be derivatized in SCer. For accurate δ(13)C of Cer in skin using GC-C-IRMS, the measured δ(13)C of a target TMS-Cer must be calculated using a correction factor representing the difference in δ(13)C of underivatized standard SCer from that of TMS-standard SCer having a structure resembling that of the target Cer in skin. In addition, we show that the same lot of TMSI reagent from a specific supplier must be used throughout the experiments.

Sealed Glass Tube Combustion of μg-Sized Aerosol Samples

It is important to evaluate each step in radiocarbon analysis to ensure that the whole process is as efficient and accurate as possible. Aerosol filter samples contain a myriad of carbonaceous compounds with varying resistance to oxidation. Complete combustion of the sample is thus of great importance to ensure that the graphitized sample is representative of the original filter sample. We have evaluated sealed tube combustion of μg-sized aerosol samples using different types and amounts of reagents. Successful analysis of aerosol samples as small as 20 μg C was possible following small changes to our standard on-line method. The sealed tube combustion method performs well for standard samples containing 11 μg C.

Small-mass AMS radiocarbon analysis at Nagoya University

As part of the ongoing development at the AMS facility of the Center for Chronological Research at Nagoya University to radiocarbon (14C) analyze samples smaller than 0.5mg carbon (mgC), a compact graphitization manifold has been built. Tests with various reference materials show it performs well for samples as small as 0.1mgC. Preparation with this new system is compared with the performance of the older protocol for regular-sized samples. Furthermore, it is shown that the addition of Cu and Ag before and stepwise heating during sealed-tube combustion of samples with high S content improve the degree of conversion to CO2 without having to resort to special purification measures such as the use of Co3O4+Ag reagent and an n-pentane/LN2 trap before graphitization.

Chlorine isotope evidence for the anthropogenic origin of tris-(4-chlorophenyl)methane

Abstract Compound-specific Cl-isotope analysis was performed on the persistent and bioaccumulating compound tris-(4-chlorophenyl)methane (4,4′,4″-TCPMe, referred to as TCPMe in this study) to elucidate whether its main source is natural or anthropogenic. Blubber from the Baltic grey seal (Halichoerus grypus) was extracted by continuous acetonitrile partitioning, and the TCPMe was isolated from the extract by preparative-capillary gas chromatography. Chlorine isotope analysis was subsequently performed by sealed-tube combustion in conjunction with thermal-ionization mass spectrometry (TIMS). The δ37Cl of TCPMe was −3.5 ± 0.5‰, similar to the previously reported δ37Cl of technical grade p,p′-DDT (referred to as DDT in this study). The data is not consistent with a putative marine natural source of TCPMe, as enzymatic (biotic) production is reported to give values of δ37Cl

Nitrogen isotopic evolution of carbonaceous matter during metamorphism: Methodology and preliminary results

Nitrogen content and isotopic composition of carbonaceous-rich metasediments were determined by on-line and sealed-tube combustion using ultra-high vacuum line and static mass spectrometer adapted to analyse nitrogen nanomoles. Accurate measurements showed that nitrogen amount released by on-line combustion technique was underestimated to various extents. As a result, the nitrogen isotopic composition was not correctly determined. In contrast, sealed-tube combustion appeared to yield the most reproducible and accurate measurements, except for nitrogen depleted carbonaceous matter (semi-graphite to graphite transition) containing less than around 60 ppm of nitrogen, which were contaminated during their extraction from the rock. In view of that, a preliminary sealed-tube investigation of the organic nitrogen content and isotopic composition in a homogenous series of low-grade metasediments was undertaken: in spite of an important nitrogen loss, the carbonaceous matter nitrogen isotopic composition remains about the same during the meta-anthracite and semi-graphitisation stages. Inferences on the process of organic nitrogen mineralization during carbonaceous matter metamorphism can be drawn and several paleo-biogeochemical implications envisaged.

Quantification and isotopic analysis of nitrogen in rocks at the ppm level using sealed tube combustion technique: A prelude to the study of altered oceanic crust

The present paper reports recent improvements in sealed tube combustion technique used for the determination of N isotopic composition in various rocks characterized by low N contents (i.e. few ppm). Nitrogen is extracted from samples by combustion in quartz tubes sealed under vacuum. The nitrogen gas purified using Cu, CuO and CaO, is quantified as dinitrogen N 2 by capacitance manometry in ultra-high vacuum line. Nitrogen isotopic analysis is performed on a triple-collector static vacuum mass spectrometer, allowing measurement of nanomole quantity of N 2. Nitrogen amount and isotopic composition of the analytical blanks are low and describe Gaussian distribution with mean values of 0.65 ± 0.30 nmol N and − 3.7‰ ± 2.7‰, respectively (2 σ). Systematic analyses of international and internal standards demonstrate that this technique provides accurate and precise results. The precision on N content and isotopic composition are better than ± 8% and ± 0.5‰ respectively, even for samples containing less than 2 ppm N. The sealed tube combustion technique is shown to apply successfully to rocks of various lithologies such as metagabbros, metaperidotites and altered basalts. It is thus suitable for studying oceanic crust in a perspective to better constrain N exchanges between Earth mantle and surface reservoirs. The investigation can also be extended to analysis of small size samples, particularly when little sample exists and when high spatial resolution is required.

Chlorine isotope analysis of submicromole organochlorine samples by sealed tube combustion and thermal ionization mass spectrometry.

Improved sensitivity in the analysis of stable chlorine isotopes of organochlorines (delta(37)Cl-OCl) has been established using sealed tube combustion in conjunction with thermal ionization mass spectrometry (TIMS). TIMS of chlorine isotopes was performed on <85 nmol of Cl with an achievable precision of <0.25 per thousand for pure inorganic chloride samples and 0.46 per thousand for chloride liberated from organochlorines (OCls). This makes possible significant reductions in the overall sample size requirement, as compared to the techniques of gas source stable isotope ratio mass spectrometry (SIRMS). Yields in excess of 99% were demonstrated in the dechlorination of <0.14 micromol 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and the overall yield, including purification of liberated chloride, was 86-97%. The accuracy of TIMS in the measurement of chlorine isotopes derived from OCls was confirmed by analysis of a DDT sample previously analyzed with SIRMS.(9) Using the described method for TIMS, the DDT sample gave a bulk chlorine isotope ratio of delta(37)Cl -4.42 +/- 0.46 per thousand (1sigma). The reported value from SIRMS analysis is -4.34 +/- 0.25 per thousand, indicating the conformity of the two methods.

Ammonium quantification in muscovite by infrared spectroscopy

Single muscovite grains of different chemical composition (in particular Si-content from 3.05 to 3.69 per formulae unit (pfu)) and origin (metamorphic and granitic rocks) were analysed by infrared (IR) spectroscopy. Their ammonium concentrations were subsequently measured by capacitance manometry after extraction as N 2 using a sealed-tube combustion technique. The values range from 0 to 2203 ppm NH 4 +. Correlation between ammonium concentration and ammonium IR absorbance corresponding to NH 4 + bending permits an assessment of the ammonium molecular absorptivity at 1430 cm −1 ( ε N–H 1430=462±32 l mol −1 cm −1). In order to avoid uncertainties on thickness estimates using an optical technique, a relationship between sample thickness and IR absorbance was determined. Ammonium concentration of muscovite can be directly derived from its IR spectrum using the relationship [NH 4 +] (ppm)=1142.5×[( A N–H 1430− A 2514)/( A 1282− A 2514)]−606 where A 1282, A N–H 1430 and A 2514 are absorbances corresponding to wavenumbers 1282 (Si–O vibration peak), 1430 (NH 4 + bending) and 2514 cm −1 (silicate network vibration), respectively. The precision of ammonium concentration estimates using this method is better than 20% (2 σ) for muscovites thicker than 30 μm. This is independent of mineral composition, thus implying that the ammonium concentration vs. IR absorbance relationship is independent of the muscovite–celadonite solid solution.

Comparison of delta18O measurements in nitrate by different combustion techniques.

Three different KNO3 salts with delta18O values ranging from about -31 to +54 per thousand relative to VSMOW were used to compare three off-line, sealed glass tube combustion methods (widely used for isotope studies) with a more recently developed on-line carbon combustion technique. All methods yielded roughly similar isotope ratios for KNO3 samples with delta18O values in the midpoint of the delta18O scale near that of the nitrate reference material IAEA-NO-3 (around +21 to +25 per thousand). This reference material has been used previously for one-point interlaboratory and intertechnique calibrations. However, the isotope ratio scale factors by all of the off-line combustion techniques are compressed such that they are between 0.3 and 0.7 times that of the on-line combustion technique. The contraction of the 6180 scale in the off-line preparations apparently is caused by O isotope exchange between the sample and the glass combustion tubes. These results reinforce the need for nitrate reference materials with delta18O values far from that of atmospheric O2, to improve interlaboratory comparability.

Evaluation of the sealed‐tube low‐temperature combustion method for the 13C/12C and 2H/1H ratio determinations of cellulose nitrate

AbstractTraditionally‐suggested combustion time of 1 h at 550°C) with the sealed‐tube combustion method for determining the 13C/ 12C ratio of cellulose nitrate or other nitrogen‐containing components could produce large negative deviation up to 1°. Three types of cellulose are used to ascertain possible causes. The presence of nitrous oxide (N2O) formed during combustion is most likely responsible for this deviation. Prolongation of the combustion time (at least 5 h at 550°C) and intimate contact between copper oxide and organic matter can greatly improve the analysis precision and effectively reduce this deviation to an acceptable level. Regardless of scattered carbon isotope data, hydrogen isotope data are all reproducible within 2° when this method is coupled with the high temperature uranium reduction method. Thus, care should be taken for determining carbon and nitrogen isotope compositions of nitrogen‐containing substances using the low temperature sealed‐tube combustion method.

AMS Radiocarbon Dating of Ancient Iron Artifacts: A New Carbon Extraction Method in Use at LLNL

A new sealed double tube combustion method was developed at Lawrence Livermore National Laboratory (LLNL) to extract carbon from modern steels and ancient iron artifacts. Iron samples were chemically pretreated with 10% nitric acid, vacuum sealed in 6 mm quartz tubes with CuO, vacuum sealed again inside 9 mm quartz tubes, and combusted at 1000 °C for a minimum of 10 hr. The resulting CO2 was graphitized routinely using hydrogen reduction (Vogel et al. 1989). After the initial phase of development, carbon yields of 100% were consistently obtained. The activities of two modern high carbon steels (treated as process blanks, manufactured using only coal as the carbon source) were determined to be 0.0077 ± 0.0009 (n = 12, ± 1 σ) for a 1.3% C steel and 0.0090 ± 0.0038 (n = 12, ± 1 σ) for a 1.9% C steel, indicating that very little contamination is introduced during the sample preparation process. Since the Iron Age began less than 5000 years ago, these background uncertainties should introduce errors of no more than ±30 years to the radiocarbon ages of actual artifacts. Two ancient iron artifacts of known date were analyzed and demonstrate that the new methodology can be used to obtain the correct date of manufacture for iron objects, provided that they are made exclusively using charcoal that was contemporaneous with the manufacture of the artifact. Since only 1 mg of carbon is required for accelerator mass spectrometry (AMS), very small iron samples can now be analyzed (50 mg of a 2.0% C iron or 1 g of a 0.1% C iron). We anticipate that this methodology will be particularly useful to archeologists who currently have to rely on context to date iron artifacts.

Formula omitted] composition of marine dissolved organic carbon

The stable isotopic composition of marine dissolved organic carbon (DOC) was measured with a high temperature, sealed tube combustion technique. The δ 13 C values of DOC ( DO 13 C) were approximately −22‰ for all samples that were collected (1) in a monthly survey conducted in Woods Hole Harbor, (2) in a spatial survey across Georges Bank during a spring bloom period, and (3) in depth profiles near Bermuda, Georges Bank and in the eastern Equatorial Pacific. The DO 13 C values were uniform in waters of varying DOC content, including low DOC deep waters and high DOC surface waters, indicating little overall isotopic fractionation during formation and degradation of marine DOC. The −22‰ DO 13 C values are similar to those observed for average marine particulate and sedimentary organic material, and exclude a large contribution from −27‰ terrestrial DOC to ocean pools.

Improved Sealed-Tube Combustion of Organic Samples to CO2for Stable Carbon Isotope Analysis, Radiocarbon Dating and Percent Carbon Determinations

Abstract The present note deals with the optimization of the combustion of organic materials to CO2 in Pyrex and quartz tubes. The influence of temperature and oxidant on the combustion yield was investigated. Different physical forms of CuO and a CuO/MnO2-mixture were used as oxidants. Possible isotopic effects during combustion were tested by gas isotope ratio mass spectrometry (GIRMS) of the CO2. Excellent results were obtained for combustion in Pyrex at 530 °C using CuO rods mixed with 20% MnO2 as oxidant. The stable isotope results for CO2 prepared with this method were accurate and showed a very good precision of 0.030 %. Applications for which quantitative combustion is a necessity, we suggest the use of CuO powder (< 100 μm) as oxidant and a combustion temperature of 850 °C.

A comparison of methods for the measurement of dissolved organic carbon in natural waters

Abstract A small suite of natural samples spanning a wide range of DOC concentrations and salinities were analyzed by three high-temperature combustion (HTC) techniques and persulfate oxidation. One of the HTC techniques, sealed-tube combustion (STC), served as a referee method. Using this method, it was possible to obtain absolute DOC concentrations for the natural samples free of any analytical blank offset. Prior to the comparison of samples, an exchange of carbon-free water and calibration standards showed that all methods were equally well calibrated. Linear correlation analysis was used to differentiate whether the differences observed between methods was due to variable oxidation yields or to an artifact of the instrument blank. Agreement among the various methods was quite good, but yields for all methods decreased compared to the STC technique at concentrations of > 400 μM C. Persulfate results were found to be very similar to HTC results. Finally, carbon-free distilled water prepared by UV H 2 O 2 oxidation or Milli-Q systems had near-zero DOC concentrations and was adequate for blank correction of all the various techniques yielding DOC concentrations in excellent agreement with the referee method.

Simplified tube cracker for opening samples sealed in glass tubes while under vacuum

A new tube cracker design has been developed that provides an inexpensive, easily adaptable and more reliable means of cracking sealed glass tubes in a vacuum system in order to transfer the products of sealed tube combustion in the preparation of samples for stable isotopic analysis. The tube cracker consists, solely, of a glass tube, closed at the bottom, and with the barrel of a vacuum stopcock sealed into the side wall. A sample tube held in the apparatus is cracked open simply by closing the tap. To accommodate sample tubes of different sizes the basic apparatus can either be adjusted using smaller or larger size tubing or the existing apparatus used to crack any smaller sized tubing by means of an insert.