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

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.     

Comments on “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” by Varlet et al.

Varlet et al. recently proposed a headspace-gas chromatography–mass spectrometry (HS-GC–MS) method applicable for the routine determination of CO₂ in gaseous biologic matrices. This developed bioanalytical method was fully validated according to the SFSTP 1997 guidelines using the accuracy profile as a graphical decision-making tool.In this letter, we discuss the validity of HS-GC–MS method based on the newest SFSTP guideline. In particular, we demonstrate by the estimation of the β-expectation tolerance interval that the error total exceeds the acceptance limits (30%) for the second concentration level (0.5 μmol mL⁻¹ vial HS).