Validation of methane measurement using headspace‐GC–MS and quantification by a stable isotope‐labeled internal standard generated in situ

A previous study has shown the possibility to identify methane ( CH 4 ) using headspace‐ GC – MS and quantify it with a stable isotope as internal standard. The main drawback of the GC – MS methods discussed in literature for CH 4 measurement is the absence of a specific internal standard necessary to perform quantification. However, it becomes essential to develop a safer method to limit the manipulation of gaseous CH 4 and to precisely control the injected amount of gas for spiking and calibration by comparison with external calibration. To avoid the manipulation of a stable isotope‐labeled gas, we have chosen to generate a labeled gas as an internal standard in a vial on the basis of the formation of CH 4 by the reaction of G rignard reagent methylmagnesium chloride with deuterated water. This method allows precise measurement of CH 4 concentrations in gaseous sample as well as in a solid or a liquid sample after a thermodesorption step in a headspace vial. A full accuracy profile validation of this method is then presented.