A fast, simple calibration method for organic carbon isotope analysis using continuous-flow elemental analyzer interfaced with an isotope ratio mass spectrometer.

Continuous flow analysis using an elemental analyzer interfaced with an isotope ratio mass spectrometer (EA-IRMS) is faster and requires much less material than conventional analytical methods. Although using an EA-IRMS is simple and fast, accurate calibration strongly depends on matching sample and reference peak heights by adjusting the sample weight. This paper describes a new modification for calibration using only the major ion beam intensity (nA) without weighing each sample or increasing the number of reference materials.     

Isotopic ((13)C) analysis of dissolved organic carbon in stream water using an elemental analyzer coupled to a stable isotope ratio mass spectrometer

A technique for measurement of the stable isotope composition of dissolved organic carbon (DOC) in stream water, using an elemental analyzer (EA) coupled to an isotope ratio mass spectrometer (IRMS), is described. Stream water samples were concentrated by rotary evaporation, acidified to remove dissolved inorganic carbon (DIC), and dried in silver cups prior to analysis. Precision was evaluated with standards (alanine and humic acid), and with stream water samples with varying (13)C enrichment. Standards and samples were also prepared in sealed quartz tubes for high-temperature combustion (HTC) and analyzed by dual inlet for comparison. The delta(13)C values of natural abundance standards and samples measured by the two techniques differed by 相似文献   

Increasing the sensitivity of delta13C and delta15N abundance measurements by a high sensitivity elemental analyzer connected to an isotope ratio mass spectrometer

A common elemental analyzer system connected to a temperature-controlled gas chromatography (GC) column and coupled to an isotope ratio mass spectrometer was improved to decrease the determination limit for a simultaneous stable isotope ratio measurement of nitrogen and carbon dioxide. The additional use of a special ashtray system to collect the combustion residuals permitted more time-efficient work. These modifications to the elemental analyzer allowed precise measurements to be made down to 1.5 microg nitrogen and 10 microg carbon for stable isotope analysis. Low system background values and an acceptable signal-to-noise ratio have made an additional blank correction for these low sample measurements unnecessary. We provide a precision of this stable isotope analysis for lowest amounts of 1.2-2 microg nitrogen with a standard deviation of +/-0.496 per thousand (n = 27) and for 8.2-15 microg carbon with a standard deviation of +/-0.257 per thousand (n = 31) across different sample runs under stipulated conditions. This application can be established in an automatic mode without cryofocusing procedures.     

Rapid 18O analysis of small water and CO2 samples using a continuous-flow isotope ratio mass spectrometer

High-frequency throughput is often needed in isotopic studies in biological and medical fields. Here we report that high-precision oxygen isotope ratio measurements of water (+/-0.13 per thousand) were rapidly and routinely made on small samples (40-100 microL) using an isotope ratio mass spectrometer operated in continuous-flow mode. Simple modifications to existing instrumentation allow for rapid manual analyses of dilute CO2 (10% CO2/90% N2), including the addition of a septum port and water trap prior to the gas chromatography (GC) column (elemental analyzer column in this study) and the extension of fused-silica capillary tubing between the mass spectrometer source and the effluent tubing from the GC column (located within the CONFLO unit on Finnigan mass spectrometers). We routinely analyzed 20 small-volume samples per hour using this technique, without sacrificing precision of the oxygen isotope ratio measurement.     

Measuring oxygen yields of a thermal conversion/elemental analyzer‐isotope ratio mass spectrometer for organic and inorganic materials through injection of CO

The thermal conversion/elemental analyzer‐isotope ratio mass spectrometer (TC/EA‐IRMS) is widely used to measure the δ¹⁸O value of various substances. A premise for accurate δ¹⁸O measurement is that the oxygen in the sample can be converted into carbon monoxide (CO) quantitatively or at least proportionally. Therefore, a precise method to determine the oxygen yield of TC/EA‐IRMS measurements is needed. Most studies have used the CO peak area obtained from a known amount of a solid reference material (for example, benzoic acid) to calibrate the oxygen yield of the sample. Although it was assumed that the oxygen yield of the solid reference material is 100%, no direct evidence has been provided. As CO is the analyte gas for δ¹⁸O measurement by IRMS, in this study, we use a six‐port valve to inject CO gas into the TC/EA. The CO is carried to the IRMS by the He carrier gas and the CO peak area is measured by the IRMS. The CO peak area thus obtained from a known amount of the injected CO is used to calibrate the oxygen yield of the sample. The oxygen yields of commonly used organic and inorganic reference materials such as benzoic acid (C₆H₅COOH), silver phosphate (Ag₃PO₄), calcium carbonate (CaCO₃) and silicon dioxide (SiO₂) are investigated at different reactor temperatures and sample sizes. We obtained excellent linear correlation between the peak area for the injected CO and its oxygen atom amount. C₆H₅COOH has the highest oxygen yield, followed by Ag₃PO₄, CaCO₃ and SiO₂. The oxygen yields of TC/EA‐IRMS are less than 100% for both organic and inorganic substances, but the yields are relatively stable at the specified reactor temperature and for a given quantity of sample. Copyright © 2014 John Wiley & Sons, Ltd.     

On-line nitrate-delta(15)N extracted from groundwater determined by continuous-flow elemental analyzer/isotope ratio mass spectrometry

Nitrate-delta(15)N from groundwater samples is determined on an inorganic nitrate derivative using automated, continuous-flow elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). Nitrate is extracted and concentrated based on a recently published ion-exchange resin method. Freeze-dried AgNO(3) (0.5-1.5 mg) is packed in silver-foil cups and combusted within the reactor of an NC2500 elemental analyzer (CE Instruments, Milan, Italy) using its existing reaction scheme for nitrogen and carbon analysis. delta(15)N is determined using a Finnigan MAT DELTA(plus) isotope ratio mass spectrometer (Bremen, Germany). Results are drift-corrected to a AgNO(3) working standard that has been calibrated against known AgNO(3). Despite high concentrations of carbonate, the precision for all runs is better than 0.10 per thousand. The combination of this extraction procedure with commercially available delta(15)N analysis instrumentation offers a precise on-line alternative to existing methods, with considerable reduction in labor and analysis time.     

Correction of mass spectrometric isotope ratio measurements for isobaric isotopologues of O2, CO,CO2, N2O and SO2

Gas isotope ratio mass spectrometers usually measure ion current ratios of molecules, not atoms. Often several isotopologues contribute to an ion current at a particular mass‐to‐charge ratio (m/z). Therefore, corrections have to be applied to derive the desired isotope ratios. These corrections are usually formulated in terms of isotope ratios (R), but this does not reflect the practice of measuring the ion current ratios of the sample relative to those of a reference material. Correspondingly, the relative ion current ratio differences (expressed as δ values) are first converted into isotopologue ratios, then into isotope ratios and finally back into elemental δ values. Here, we present a reformulation of this data reduction procedure entirely in terms of δ values and the ‘absolute’ isotope ratios of the reference material. This also shows that not the absolute isotope ratios of the reference material themselves, but only product and ratio combinations of them, are required for the data reduction. These combinations can be and, for carbon and oxygen have been, measured by conventional isotope ratio mass spectrometers. The frequently implied use of absolute isotope ratios measured by specially calibrated instruments is actually unnecessary. Following related work on CO₂, we here derive data reduction equations for the species O₂, CO, N₂O and SO₂. We also suggest experiments to measure the required absolute ratio combinations for N₂O, SO₂ and O₂. As a prelude, we summarise historic and recent measurements of absolute isotope ratios in international isotope reference materials. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of the 13C natural abundance of CO2 gas from sparkling drinks by gas chromatography/combustion/isotope ratio mass spectrometry

A simple and rapid method to measure naturally occurring delta(13)C values of headspace CO(2) of sparkling drinks has been set up, using direct injections on a gas chromatograph coupled to an isotope ratio mass spectrometer, through a combustion interface (GC/C/IRMS). We tested the method on CO(2) gas from several origins. No significant isotopic fractionation was observed nor influences by secondary compounds eventually present in the gas phase. Standard deviation for these measurements was found to be <0.1 per thousand.     

A versatile method for stable carbon isotope analysis of carbohydrates by high-performance liquid chromatography/isotope ratio mass spectrometry

We have developed a method to analyze stable carbon isotope ((13)C/(12)C) ratios in a variety of carbohydrates using high-performance liquid chromatography/isotope ratio mass spectrometry (HPLC/IRMS). The chromatography is based on strong anion-exchange columns with low strength NaOH eluents. An eluent concentration of 1 mM resulted in low background signals and good separation of most of the typical plant neutral carbohydrates. We also show that more strongly bound carbohydrates such as acidic carbohydrates can be separated by inclusion of NO(3) (-) as an inorganic pusher ion in the eluent. Analyses of neutral carbohydrate concentrations and their stable carbon isotope ratios are shown for plant materials and marine sediment samples both at natural abundance and for (13)C-enriched samples. The main advantage of HPLC/IRMS analysis over traditional gas chromatography based methods is that no derivatization is needed resulting in simple sample treatment and improved accuracy and reproducibility.     

Validation of pentaacetylaldononitrile derivative for dual 2H gas chromatography/mass spectrometry and 13C gas chromatography/combustion/isotope ratio mass spectrometry analysis of glucose

A reference method to accurately define kinetics in response to the ingestion of glucose in terms of total, exogenous and endogenous glucose is to use stable‐isotope‐labelled compounds such as ²H and ¹³C glucose followed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analysis. The use of the usual pentaacetyl (5Ac) derivative generates difficulties in obtaining accurate and reproducible results due to the two chromatographic peaks for the syn and anti isomers, and to the isotopic effect occurring during acetylation. Therefore, the pentaacetylaldononitrile derivative (Aldo) was validated for both isotopes, and compared with the 5Ac derivative. A correction factor including carbon atom dilution (stoichiometric equation) and the kinetic isotopic effect (KIE) was determined. Analytical validation results for the ²H GC/MS and ¹³C GC/C/IRMS measurements produced acceptable results with both derivatives. When ²H enrichments of plasma samples were ≤1 mol % excess (MPE), the repeatability (RSD_{Aldo Intra assay and Intra day} <0.94%, RSD_{5Ac Intra assay and Intra day} <3.29%), accuracy (Aldo <3.4%, 5Ac <29.0%), and stability of the derivatized samples were significantly better when the Aldo derivatives of the plasma samples were used (p < 0.05). When the glucose kinetics were assessed in nine human subjects, after glucose ingestion, the plasma glucose ²H enrichments were identical with both derivatives, whereas the ¹³C enrichments needed a correction factor to fit together. Due to KIE variation, this correction factor was not constant and had to be calculated for each batch of analyses, to obtain satisfactory results. Mean quantities of exogenous glucose exhibit marked difference (20.9 ± 1.3g (5Ac) vs. 26.7 ± 2.5g (Aldo)) when calculated with stoichiometric correction, but fit perfectly when calculated after application of the correction factor (22.1 ± 1.3g (5Ac) vs. 22.9 ± 1.9g (Aldo)). Finally, the pentaacetylaldononitrile derivative, used here in GC/C/IRMS for the first time, enables measurement of ²H and ¹³C enrichments in plasma glucose with a single sample preparation. Copyright © 2009 John Wiley & Sons, Ltd.     

Methods to reduce interference effects in thermal conversion elemental analyzer/continuous flow isotope ratio mass spectrometry delta18O measurements of nitrogen-containing compounds

On-line determination of the oxygen isotopic composition (delta(18)O value) in organic and inorganic samples is commonly performed using a thermal conversion elemental analyzer (TC-EA) linked to a continuous flow isotope ratio mass spectrometry (IRMS) system. Accurate delta(18)O analysis of N-containing compounds (like nitrates) by TC-EA-IRMS may be complicated because of interference of the N(2) peak on the m/z 30 signal of the CO peak. In this study we evaluated the effectiveness of two methods to overcome this interference which do not require any hardware modifications of standard TC-EA-IRMS systems. These methods were (1) reducing the amount of N(2) introduced into the ion source through He dilution of the N(2) peak and (2) an improved background correction on the CO m/z 30 sample peak integration.Our results show that He dilution is as effective as diverting the N(2) peak in order to eliminate this interference. We conclude that the He-dilution technique is a viable method for the delta(18)O analysis of nitrates and other N-containing samples (which are not routinely measured using He dilution) using TC-EA-IRMS, since it can easily be programmed in the standard software of IRMS systems. With the He-dilution technique delta(18)O values of the nitrate isotope standards USGS34, IAEA-N3 and USGS35 were measured using the shortest possible traceability chain to the VSMOW-SLAP scale, and the results were -28.1 +/- 0.1 per thousand, +25.5 +/- 0.1 per thousand and +57.5 +/- 0.2 per thousand, respectively. An improved background correction was also an effective method, but required manual correction of the raw data.