[en] Unrepeatability of gas quantitative mass-spectrometric analysis caused by mass variation of tracer gas added as internal standard due to changing temperature conditions in the dosing system between two experiments is estimated. The tracer dosing system consists of a large capacity V₁ containing the tracer and a small capacity V₂ connected to the first one via a valve. The tracer out of the V₂ capacity is bleeded into the V₃ analytical capacity through the second valve where there is the gas under investigation. The mixture of the latter one with tracer then immediately or after purification is bleeded into the mass-spectrometer cell. It follows from the above analysis that the most straightforward method for improving tracer dosing repeatability is to enclose the V₁ and V₂ capacities into a general effective thermostat