A combination of gas chromatography, combustion, and 13C/12C isotope dilution mass spectrometry (GC/C/IDMS)

Isotope amount ratios are proving useful in an ever increasing array of applications that range from studies unravelling transport processes, to pinpointing the provenance of specific samples as well as trace element quantification by using isotope dilution mass spectrometry (IDMS). These expanding applications encompass fields as diverse as archaeology, food chemistry, forensic science, geochemistry, medicine and metrology. However, to be effective tools, the isotope ratio data must be reliable and traceable to enable the comparability of measurement results.The importance of traceability and comparability in isotope ratio analysis has already been recognized by the Inorganic Analysis Working Group (IAWG) within the CCQM. While the requirements for isotope ratio accuracy and precision in the case of IDMS are generally quite modest, 'absolute' Pb isotope ratio measurements for geochemical applications as well as forensic provenance studies require Pb isotope ratio measurements of the highest quality. To support present and future CMCs on isotope ratio determinations, a key comparison was urgently needed and therefore initiated at the IAWG meeting in Paris in April 2011. The analytical task within such a comparison was decided to be the measurement of Pb isotope amount ratios in water and bronze.Measuring Pb isotope amount ratios in an aqueous Pb solution tested the ability of analysts to correct for any instrumental effects on the measured ratios, while the measurement of Pb isotope amount ratios in a metal matrix sample provided a real world test of the whole chemical and instrumental procedure. A suitable bronze material with a Pb mass fraction between 10 and 100 mg•kg-1 and a high purity solution of Pb with a mass fraction of approximately 100 mg•kg-1 was available at the pilot laboratory (BAM), both offering a natural-like Pb isotopic composition.The mandatory measurands, the isotope amount ratios n(206Pb)/n(204Pb), n(207Pb)/n(204Pb) and n(208Pb)/n(204Pb) were selected such that they correspond with those commonly reported in Pb isotopic studies and fully describe the isotopic composition of Pb in the sample. Additionally, the isotope amount ratio n(208Pb)/n(206Pb) was added, as this isotope ratio is typically measured when performing Pb quantitation by IDMS involving a 206Pb spike.Each participant was free to use any method they deemed suitable for measuring the individual isotope ratios. However, the majority of the results were obtained by using muIti-collector ICPMS or TIMS. The key requirements for all analytical procedures were a traceability statement for all results and the establishment of an uncertainty budget meeting a target uncertainty for all ratios of 0.2 %, relative (k=1). Additionally, the use of a Pb-matrix separation procedure was encouraged.The obtained overall result was excellent, demonstrating that the individual results reported by the NMIs/DIs were comparable and compatible for the determination of Pb isotope ratios. MC-ICPMS and MC-TIMS data were consistent with each other and agree to within 0.05 %. The corresponding uncertainties can be considered as realistic uncertainties and mainly range from 0.02 % to 0.08 % (k=1).As stated above isotope ratios are being increasingly used in different fields. Despite the availability and ease of use of new mass spectrometers, the metrology of unbiased isotope ratio measurements remains very challenging. Therefore, further comparisons are urgently needed, and should be designed to also engage scientists outside the NMI/DI community. Possible follow-up studies should focus on isotope ratio and delta measurements important for environmental and technical applications (e.g. B), food traceability and forensics (e.g. H, C, N, O, S and 87Sr/86Sr) or climate change issues (e.g. Li, B, Mg, Ca, Si).Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM.

Fundamental studies on isotope ratio measurement of Cl were carried out using inductively coupled plasma triple-quad mass spectrometry (ICP-MS/MS) and the analytical performance obtained was compared to that obtained by ICP sector field mass spectrometer (ICP-SFMS). Though the polyatomic ion interferences of 16O18O1H and 36Ar1H with respect to 35Cl and 37Cl, respectively, made a negative effect on the accuracy and the precision for isotope ratio measurements of Cl, the ICP-SFMS could eliminate these interferences by medium mass resolution mode (m/Δm = 4000) and achieved the isotope ratio measurements with 0.2 - 0.5% of relative standard deviation (RSD) at the concentrations of Cl from 1 to 10 mg kg-1. In the case of ICP-MS/MS, both the single-MS mode without collision reaction gas and the MS/MS mode with collision reaction gases such as oxygen (O2) and hydrogen (H2) were examined and compared their analytical sensitivities as well as the precisions of isotope ratio measurement of Cl. The precisions of Cl isotope ratio measurements were 3 - 14% of RSD at the concentrations of Cl from 5 to 100 mg kg-1, when single-MS mode was carried out, even though the similar isotope ratios of 35Cl/37Cl could be obtained. In the case of O2 gas for MS/MS mode with mass-shift method, precisions of 0.3 - 2% of RSD were obtained at the concentration range of 1 - 100 mg kg-1. In the case of H2 gas, similar sensitivities as those obtained by ICP-SFMS and the precisions of 0.2 - 0.5% of RSD at the concentration range of 1 - 10 mg kg-1 were obtained. From these results, it was evaluated that the ICP-MS/MS in MS/MS mode with collision reaction gas could be used for Cl isotope ratio measurements for such studies as stable isotope tracers, isotope abundance measurements in nuclear chemistry and accurate determinations by isotope dilution mass spectrometry.

Examination on simultaneous multi-element isotope ratio measurement by inductively coupled plasma time of flight mass spectrometry

The combination of gas chromatography, combustion, and isotope ratio monitoring (IRM-GC/MS) is usually used for measuring small variations of the isotope ratios of carbon and nitrogen in organic chemical compounds. This technique is very well developed in terms of both instrumentation and methodology. High precision is, therefore, attained in isotope ratio mesurements. It has been the aim of our investigation to check the applicability of the IRM-GC/MS technique for the quantitative analysis of organic chemical compounds using the isotope dilution technique. The influence of the different steps of the instrumental setup on the uncertainty of the isotope ratio measurement was investigated. It follows from the results that the chromatographic separation in connection with the combustion of the analyte exerts the strongest influence on the uncertainty of the measurement results. The suitability of the method for amount-of-substance measurements has been checked by investigating model mixtures of carboxylic acids. The results exhibit low values of the relative type A standard uncertainty of 2 × 10−3. It is the main feature of the new method that, on the one hand, the conversion of the analyte to carbon dioxide makes it possible to measure the n(13C)/n(12C) isotope ratio with a high precision. On the other hand, the high selectivity of mass spectrometry is lost due to the combustion step. © 1998 John Wiley & Sons, Ltd.

Preparation of 241Am/243Am gravimetric mixtures and development of Am isotopic and assay measurement techniques using thermal ionization mass spectrometry

Isotopic analyses of inorganic and organic substances by mass spectrometry

The radionuclide Ar39 is produced in the atmosphere by cosmic rays and has an isotopic abundance of 8.1×10−16. Because its half life (T1/2=269 years) is well matched to the time periods involved in the oceanic currents around the Earth, the measurement of the Ar39 isotopic ratio is an ideal tool to date ocean water from different depths. It would complement the information gained by the C14 measurements (T1/2=5730 years). However, the measurement of the isotopic ratio Ar39/Ar40 is a technical challenge: 1 L of modern ocean water contains ∼6500 atoms of Ar39, and produces ∼17 decays per year. Although it has been possible to detect the Ar39 decays in large volumes of sea water by using the low level counting technique, the possibility of measuring the number of Ar39 atoms faster and in smaller samples using the accelerator mass spectrometry (AMS) technique would be a major breakthrough for this type of measurement. The development of a viable AMS method for Ar39 has been underway for several years at Argonne National Laboratory, and is presently hampered by the presence of stable K39 ions coming from the ion source. Although the intensity of this isobaric contaminant is low (∼pA extracted from the source), it has to be compared with the Ar39 beam intensity (atoms per minutes). In order to separate these two beams (whose mass difference is only 1.6×10−5), the intensity of the K39 beam coming from the ion source has to be reduced by several orders of magnitude. This reduction has been investigated both at Argonne National Laboratory and at Louvain-la-Neuve. Two techniques have been tried out. In the first, a quartz liner is used to provide a clean surface, while in the second these impurities are buried in a SiO2 layer formed in situ by running the source with a mixture of silane and oxygen. The K39 background has been reduced by a factor of 100 with these treatments. These techniques and their results obtained both at Argonne and Louvain-la-Neuve will be presented. The ion source specific requirements for this type of application will also be discussed.

The measurement of isotope ratios (within individual species), for a range of organolead compounds, was carried out by coupling a capillary gas chromatograph (HP 6890) to an inductively coupled plasma mass spectrometer (HP 4500). Optimum conditions for the separation and detection of the derivatised lead organometallic compounds were studied focusing on the precise and accurate measurement of isotope ratios on each chromatographic peak. Three lead isotopes were monitored, 206, 207 and 208 using 66 ms integration time per isotope. Under optimum conditions adequate chromatographic peak profiles could be measured. Based on peak area ratios, isotope ratios were determined for five butylated lead compounds (trimethyllead, dimethyllead, triethyllead, diethyllead and inorganic lead) and mixed methyl-ethyl tetraalkyllead compounds from leaded gasoline. Mass bias was corrected using both ethylated and butylated NIST 981 isotopic standard (Common Lead) and a certified enriched 204Pb solution. No isotope fractionation effects were observed during derivatisation of the different organometallic compounds. Applications of this methodology include the differentiation between Pb sources of the different standards used, the measurement of Pb isotope ratios in the organolead compounds present in airborne particulate matter of Oviedo to ascertain their origin and the comparison with isotope ratios in the BCR CRM 605 urban dust reference material. Significant differences between lead isotope ratios in the different species of organolead compounds and in total lead (after acid digestion of the samples) were observed. These differences can be used to trace back sources of lead contamination, by resorting to the speciation data, in cases where the isotope ratios of total lead in the samples are inconclusive in identifying Pb contamination sources.

Isotope dilution mass spectrometry for quantitative elemental analysis of powdered samples by radiofrequency pulsed glow discharge time of flight mass spectrometry

A new method for the measurement of calcium isotope ratios and total calcium, using a double focusing sector field inductively coupled plasma mass spectrometry (ICP-MS) instrument equipped with a shielded torch, is presented. The method was applied for the measurement of the 44Ca/43Ca, 42Ca/43Ca and 44Ca/42Ca ratios and total calcium by isotope dilution in urine samples from two different nutritional experiments set up to determine the calcium absorption from various foods. The isotope ratios were measured with a precision of 0.25%, 0.23% and 0.05% RSD for 44Ca/43Ca, 42Ca/43Ca and 44Ca/42Ca, respectively. The precision of the 44Ca/42Ca ratio is only limited by counting statistics, whereas the precision is limited by uncertainty from the needed background and interference corrections when the minor 43Ca isotope is used for analysis. Uncertainty calculations on the determination of calcium absorption in the nutritional experiments are presented. These calculations show that, for a double stable isotope procedure (administration of enriched stable 44Ca and 42Ca), the overall uncertainty is controlled by the precision of the ICP-MS measurement of the isotope ratios (44Ca/43Ca, 42Ca/43Ca), whereas, for a mixed radioisotope–stable isotope procedure (administration of enriched stable 44Ca and the 47Ca radioisotope), the overall uncertainty is mainly controlled by the uncertainty in the measurement of total calcium by isotope dilution ICP-MS. From these results, it was concluded that, when optimizing the performance of nutritional experiments, the emphasis should be placed on different parameters depending on the exact analysis involved. The results also show that uncertainty calculations are very useful in pinpointing the critical parameters of an experiment.

Comprehensive two-dimensional gas chromatography in combination with rapid scanning quadrupole mass spectrometry in perfume analysis

Application of the 2 f-wavelength modulation technique for the measurement of large lithium isotope ratios by diode laser graphite furnace atomic absorption spectroscopy

Isotope dilution mass spectrometry (IDMS) as a definitive method is a sensitive analytical technique for accurate trace analysis down to the sub-ppb level. The application of IDMS requires precise and accurate isotope ratio measurements. It has been demonstrated that these measurements can be carried out with a small, cost-efficient and easy-to-use quadrupole mass spectrometer equipped with both a Faraday detector and a secondary electron multiplier (SEM). Here we describe a new detector system for this instrument which allows pulse counting measurements of both positive and negative ions. The performance of the new detector system is shown for I, Sr and Nd isotope ratio measurements. A synthetic mixture of127I and129I was measured using negative thermal ionisation. The127I/129I isotope ratio was determined with a relative external precision of 0.6% using I loadings of 0.08 and 0.8 nmol. For Sr and Nd isotope ratios a relative external precision of 0.1%–0.2% and an accuracy of 0.06% were obtained for loadings of 0.01 to 0.05 nmol.

A gas chromatography electron capture negative ionization mass spectrometry (GC(ECNI)MS) procedure for the determination of priority polybrominated diphenyl ethers (PBDEs; congeners 28, 47, 99, 100, 153 and 154) in water samples at regulatory EU levels has been developed. The method is based on the use of (81)Br-labelled PBDEs for isotope dilution analysis and the measurement of (79)Br/(81)Br isotope ratios in gas chromatography peaks with the electron capture negative ionization technique. The suitability of this ion source for the precise and accurate measurement of bromine isotope ratios has been demonstrated. The general ECNI-IDMS procedure was evaluated by the analysis of NIST SRM 1947 (Lake Michigan fish tissue) with satisfactory results. For the analysis of water samples, 500 mL of the samples were spiked with the labelled PBDEs and extracted with 10 mL isooctane for 30 min. The extract was evaporated down to ca. 100 μL and injected in the GC(ECNI)MS. Detection limits ranged from 0.014 (-1) to 0.089 pg mL(-1) depending on the congener. Recoveries from real water samples, spiked at a level of 0.5 pg mL(-1), ranged from 77% to 102%.

The present work assessed the purity of [Glu1]-fibrinopeptide B (GFB) as a model peptide using gas chromatography - isotope dilution mass spectrometry. GFB and various isotope-labeled amino acids were hydrolyzed in HCl and then derivatized using optimized procedures. The primary impurity in GFB was also identified and used to correct the final result. A method repeatability of 0.5% was achieved and linear calibrations were obtained for five amino acids. The LOD and LOQ were 0.041 to 0.096 μg g-1, and 0.16 to 0.56 μg g-1, respectively. The purity of GFB was found to be (0.715 ± 0.012) g g-1. This technique exhibited comparable accuracy to that obtainable from liquid chromatography - isotope dilution mass spectrometry but at lower cost. This method could be employed as a reference technique or in fields such as clinical diagnostics or bio-pharmaceutical peptide purity analysis.