title: The influence of different referencing methods on the accuracy of δ(13) C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry.
abstract: BACKGROUND
  Brazil is the largest producer of sugar cane bioethanol in the world. Isotope ratio mass spectrometry (IRMS) is the technique of choice to certify the origin/raw materials for ethanol production, but the lack of certified reference materials (CRMs) for accurate measurements of δ(13) C values traceable to Vienna Pee Dee Belemnite (VPDB), the international zero point for (13) C/(12) C measurements, certified and compatible with gas chromatography (GC)/IRMS instruments may compromise the accuracy of δ(13) C determinations.
  
  
  METHODS
  We evaluated the influence of methods for the calibration and normalization of raw δ(13) C values of ethanol samples. Samples were analyzed by GC/C/IRMS using two different GC columns. Different substances were used as isotopic standards for the working gas calibration. The δ(13) C values obtained with the three methods of normalization were statistically compared with those obtained with elemental analyzer (EA)/IRMS, since the δ(13) C results obtained using EA are traceable to VPDB via the NBS 22 reference material.
  
  
  RESULTS
  It was observed that both the isotopic reference material for CO2 calibration and the GC column have a major effect on the δ(13) C measurements, leading to a bias of almost 2-3 ‰ in the δ(13) C values. All three methods of normalization were equivalent in performance, enabling an improvement in the GC/C/IRMS accuracy, compared with the EA/IRMS reference values for the samples.
  
  
  CONCLUSIONS
  All the methods of CO2 calibration, chromatography and normalization presented in this work demonstrated several sources of traceability and accuracy loss for the determination of δ(13) C values in ethanol fuel samples by GC/C/IRMS. This work has also shown the importance of using proper CRMs traceable to VPBD that should be compatible and certified using GC/C/IRMS, ideally in a wide range of δ(13) C values. This is important not only for bioethanol fuel samples, but also for many analytes commonly analyzed by IRMS.
authors.affiliation: National Institute of Metrology, Quality and Technology -INMETRO, Division of Chemical Metrology, 25250-020, Duque de Caxias, RJ, Brazil.|Laboratory of Green Technologies - GREENTEC, School of Chemistry, Federal University of Rio de Janeiro (UFRJ), Technology Center, 21941-909, Rio de Janeiro, RJ, Brazil.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Neves
authors.affiliation: National Institute of Metrology, Quality and Technology -INMETRO, Division of Chemical Metrology, 25250-020, Duque de Caxias, RJ, Brazil.
authors.forename: Janaína M
authors.initials: JM
authors.lastname: Rodrigues
authors.affiliation: National Institute of Metrology, Quality and Technology -INMETRO, Division of Chemical Metrology, 25250-020, Duque de Caxias, RJ, Brazil.
authors.forename: Romeu J
authors.initials: RJ
authors.lastname: Daroda
authors.affiliation: National Institute of Metrology, Quality and Technology -INMETRO, Division of Chemical Metrology, 25250-020, Duque de Caxias, RJ, Brazil.
authors.forename: Paulo R M
authors.initials: PR
authors.lastname: Silva
authors.affiliation: PETROBRAS Research and Development Center - CENPES, Division of Geochemistry, 21941-915, Ilha do Fundão, Rio de Janeiro, RJ, Brazil.
authors.forename: Alexandre A
authors.initials: AA
authors.lastname: Ferreira
authors.affiliation: Laboratory of Green Technologies - GREENTEC, School of Chemistry, Federal University of Rio de Janeiro (UFRJ), Technology Center, 21941-909, Rio de Janeiro, RJ, Brazil.
authors.forename: Donato A G
authors.initials: DA
authors.lastname: Aranda
authors.affiliation: National Institute of Metrology, Quality and Technology -INMETRO, Division of Chemical Metrology, 25250-020, Duque de Caxias, RJ, Brazil.|ThoMSon Mass Spectrometry Laboratory, Institute of Chemistry, University of Campinas - UNICAMP, 13083-970, Campinas, SP, Brazil.
authors.forename: Marcos N
authors.initials: MN
authors.lastname: Eberlin
authors.affiliation: National Institute of Metrology, Quality and Technology -INMETRO, Division of Chemical Metrology, 25250-020, Duque de Caxias, RJ, Brazil.|ThoMSon Mass Spectrometry Laboratory, Institute of Chemistry, University of Campinas - UNICAMP, 13083-970, Campinas, SP, Brazil.
authors.forename: Maíra
authors.initials: M
authors.lastname: Fasciotti