Elsevier

Analytica Chimica Acta

Volume 784, 19 June 2013, Pages 42-46
Analytica Chimica Acta

Innovative method for carbon dioxide determination in human postmortem cardiac gas samples using headspace-gas chromatography–mass spectrometry and stable labeled isotope as internal standard

https://doi.org/10.1016/j.aca.2013.04.046Get rights and content

Highlights

  • We developed a method for CO2 analysis in cardiac samples and quantification by 13CO2.

  • This method was fully validated by accuracy profile.

  • We have applied this method to perform CO2 precise quantification for forensic applications.

  • Context of the death could be documented following CO2 concentrations.

Abstract

A novel approach to measure carbon dioxide (CO2) in gaseous samples, based on a precise and accurate quantification by 13CO2 internal standard generated in situ is presented. The main goal of this study was to provide an innovative headspace-gas chromatography–mass spectrometry (HS-GC–MS) method applicable in the routine determination of CO2. The main drawback of the GC methods discussed in the literature for CO2 measurement is the lack of a specific internal standard necessary to perform quantification. CO2 measurement is still quantified by external calibration without taking into account analytical problems which can often occur considering gaseous samples. To avoid the manipulation of a stable isotope-labeled gas, we have chosen to generate in situ an internal labeled standard gas (13CO2) on the basis of the stoichiometric formation of CO2 by the reaction of hydrochloric acid (HCl) with sodium hydrogen carbonate (NaH13CO3). This method allows a precise measurement of CO2 concentration and was validated on various human postmortem gas samples in order to study its efficiency.

Introduction

Carbon dioxide acts as an asphyxiant because of the decrease of oxygen availability, and as a narcotic and respiratory stimulant agent. Exposure at CO2 levels higher than 20% presents a very high risk of a fatal accident, also considering the odorless feature of this gas. Smaller CO2 concentrations can cause troubles from convulsions and comas to death for individuals with pathologies, especially if the oxygen tension is lowered [1], [2]. Moreover, the odorless property of CO2 makes it even more noxious. It can be generated by neutral geothermal emissions, fermentative processes or by human and industrial activities. As a result, works in fermented environments [1], [3], [4], [5] and refrigerated storage by dry ice (solid CO2) [6], [7], [8], [9], [10], which are known to produce CO2, were responsible for various lethal cases. However, only CO2 concentration in the ambient air was measured and assessed to indicate toxic and lethal concentration range. Indeed, no information about a lethal CO2 concentration in blood or other biological matrices is available. The value of carbon dioxide could also be a crucial parameter to differentiate between vital air embolism, decompression/compression accident and body decomposition and therefore it can play an important role for defining the cause of death [11], [12], [13].

Determination of CO2 concentration is usually conducted by infrared gas analysis or chemical analysis (an alkali trap and subsequent titration, or soda lime absorption). However, these methods are either unavailable in many laboratory or too time consuming to be used as a routine investigation [14]. Gas chromatography coupled to mass spectrometry allows a more precise identification of the analyte through the acquisition of the mass spectrum [15], [16]. Other detectors coupled to gas chromatography such as flame ionization detector (FID) with a methanizer placed before the detector [17], [18] or thermal conductivity detector (TCD) [19], [20] were also used but without reaching the detection limit of mass spectrometry. Nevertheless, the quantification is always carried out with external calibrations [21]. These procedures can give a satisfactory estimation of carbon dioxide concentrations but the use of an internal standard could be of a great benefit to take into account eventual gas losses during sampling and analysis.

A previous study about in situ generation of carbon monoxide and 13C carbon monoxide had explained the safe generation of such gases [22] from the action of hot sulfuric acid on formic acid (HCOOH) and 13C formic acid (H13COOH). This work has already presented the advantage of normalizing CO concentrations by an internal isotopically-labeled standard. From the action of hydrochloric acid (HCl) on sodium hydrogenocarbonate (NaHCO3) and 13C sodium hydrogenocarbonate (NaHCO3) at high temperature, it becomes possible to generate CO2 and 13CO2.

The aim of our study was to present an innovative HS-GC/MS method applicable for the determination of carbon dioxide in gaseous biological matrices. The analytical protocol is fully described and is subsequently applied to measure CO2 in biological matrices from autopsied cadavers in which a gas formation was identified.

Section snippets

Materials and reagents

Hydrochloric acid (HCl, purity 32%) and sodium hydrogen carbonate (NaHCO3) were purchased from Merck (Darmstadt, Germany). 13C sodium hydrogen carbonate (NaH13CO3) (13C purity, 99%) was obtained from Cambridge Isotope Laboratories CIL Inc. (Andover, USA). All headspace extractions were carried out in headspace vials of 20 mL. Certified CO2 cylinder (purity of 99.998%) used as external control and all the analytical gases used were from Carbagaz (Lausanne, Switzerland).

Extraction method

CO2 and 13CO2 were

Validation of the analytical method

The selectivity of the method was investigated by analysing CO2 in various gaseous mixtures containing alkanes, alkenes and permanent gas. All these analyses were evaluated for co-eluting chromatographic peaks that might interfere with the detection of CO2 or 13CO2. No interference peak was observed at the considered retention time and for the m/z of 44 and 45, indicating that the method provides satisfactory selectivity for CO2 determination (Fig. 3).

The validation range was deliberately

Conclusion

A selective and sensitive method for the identification and quantification of CO2 in human cardiac gaseous postmortem samples was presented. This method offers a new opportunity of precise CO2 measurement in forensic sciences, particularly for postmortem cases showing gas occurences. It gives also precious information about the context and the cause of the death in cases of putrefied bodies. This method based on stable labeled isotope generation of CO2 allows an accurate and reliable

Acknowledgments

The authors would like to thank the entire team of the forensic project “Forensic Imaging and Putrefaction Gases”, especially Christine Chevallier, Christine Bruguier, Alain Bouvet and Marcin Simiaszko for the samples collections, the Forensic Medicine Unit and the Forensic Toxicology and Chemistry Unit of the University Center of Legal Medicine in Lausanne.

References (28)

  • C.C. Hsieh et al.

    Am. J. Emerg. Med.

    (2005)
  • V. Varlet et al.

    J. Chromatogr. B

    (2012)
  • H.I. Williams et al.

    Br. Med. J.

    (1958)
  • N.J. Langford

    Toxicol. Rev.

    (2005)
  • H. Sato et al.

    J. UOEH

    (2009)
  • F.M. Troisi

    Br. J. Ind. Med.

    (1957)
  • M.P. Guillemin et al.

    Ann. Occup. Hyg.

    (1994)
  • M. Yamazaki et al.

    Nihon Hoigaku Zasshi

    (1997)
  • V.D. Khokhlov

    Sud. Med. Ekspert.

    (1996)
  • E. Norimine et al.

    Chudoku Kenkyu

    (2009)
  • S. Srisont et al.

    J. Forensic Sci.

    (2009)
  • Y. Bernaldo de Quiros et al.

    Sci. Rep.

    (2011)
  • T. Bajanowski et al.

    Int. J. Legal Med.

    (1998)
  • T. Bajanowski et al.

    Int. J. Legal Med.

    (1998)
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