title: Modification of a commercial gas chromatography isotope ratio mass spectrometer for on-line carbon isotope dilution: Evaluation of its analytical characteristics for the quantification of organic compounds.
abstract: We describe the instrumental modification of a commercial gas chromatography isotope ratio mass spectrometer (GC-IRMS) and its application for on-line carbon isotope dilution. The main modification consisted in the addition of a constant flow of enriched (13)CO2 diluted in helium after the chromatographic column through the splitter holder located inside the chromatographic oven of the instrument. In addition, and in contrast to the conventional mode of operation of GC-IRMS instruments where the signal at m/z 45 is amplified 100-fold with respect to the signal at m/z 44, the same signal amplification was used in both Faraday cups at m/z 44 and 45. Under these conditions isotope ratio precision for the ratio 44/45 was around 0.05% RSD (n=50). The evaluation of the instrument was performed with mixtures of organic compounds including 11 n-alkanes, 16 PAHs, 12 PCBs and 3 benzothiophenes. It was observed that compounds of very different boiling points could be analysed without discrimination in the injector when a Programmable Temperature Vaporizer (PTV) injector was employed. Moreover, the presence of heteroatoms (Cl or S) in the structure of the organic compounds did not affect their combustion efficiency and therefore the trueness of the results. Quantitative results obtained for all the analytes assayed were excellent in terms of precision (<3% RSD) and accuracy (average relative error≤4%) and what is more important using a single and simple generic internal standard for quantification.
authors.affiliation: Department of Physical and Analytical Chemistry, University of Oviedo, Julián Clavería 8, 33006 Oviedo, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Alonso Sobrado
authors.affiliation: Department of Physical and Analytical Chemistry, University of Oviedo, Julián Clavería 8, 33006 Oviedo, Spain.
authors.forename: Mario
authors.initials: M
authors.lastname: Robledo Fernández
authors.affiliation: Department of Physical and Analytical Chemistry, University of Oviedo, Julián Clavería 8, 33006 Oviedo, Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Cueto Díaz
authors.affiliation: Department of Physical and Analytical Chemistry, University of Oviedo, Julián Clavería 8, 33006 Oviedo, Spain. Electronic address: ruizjorge@uniovi.es.
authors.forename: Jorge
authors.initials: J
authors.lastname: Ruiz Encinar
authors.affiliation: Department of Physical and Analytical Chemistry, University of Oviedo, Julián Clavería 8, 33006 Oviedo, Spain. Electronic address: jiga@uniovi.es.
authors.forename: J Ignacio
authors.initials: JI
authors.lastname: García Alonso
mesh_terms: D000473:Alkanes / Q000032:analysis*; D002247:Carbon Isotopes; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D007201:Indicator Dilution Techniques; D011078:Polychlorinated Biphenyls / Q000032:analysis*; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis*; D013876:Thiophenes / Q000032:analysis*
chemical_list: D000473:Alkanes; D002247:Carbon Isotopes; D011084:Polycyclic Aromatic Hydrocarbons; D013876:Thiophenes; D011078:Polychlorinated Biphenyls
keywords: Combustion; Compound-independent calibration; Gas chromatography; Mass spectrometry; On-line isotope dilution