<p>The accuracy of the online quantification of gaseous effluents from
catalytic reactors by mass spectrometry (MS) is rarely addressed by
researchers, despite the extensive use of the technique. MS results are
strongly sensitive to both the operation conditions of the reactor and to the
state of the instrument. Therefore, most studies use them as qualitative
descriptors of the performance of catalytic reaction systems. The purpose of
this work was to develop an accurate method for the quantification of gaseous
effluents from catalytic reactors. For this purpose, the mathematical
expressions from the so-called external and internal standard calibration
methods for MS were coupled to the typical metrics used for studying catalytic
reactions; namely, conversion, selectivity, and carbon mass balances. The
catalytic combustion of methane was selected as a model reaction to test the
developed approach. The accuracy of the developed method was validated by
comparison with results obtained in a separated reaction system coupled online
to a gas chromatograph. The closure of the carbon mass balance was used as a
control metrics allowing for the assessment of the physical meaning of the
method. In general, the internal standard method of calibration was found to be
best for the accurate quantification of gaseous streams by on-line mass
spectrometry. In general, the results of this investigation may be of use to
researchers in the field of catalysis as well as to research workers using mass
spectrometry for various purposes.</p>