The influence of several experimental parameters such as concentration of the analyzed species, temperature, flow rate and properties of the carrier gas, on the sensitivity of the mass spectrometric analysis in a TA-MS system Netzsch STA 409 thermoanalyzer coupled via a heated capillary with a Balzers QMG 420 quadrupole mass spectrometer has been investigated. The determination of the calibration factor, facilitating the quantification of the MS signal, was carried out by means of two methods : decomposition of solids and injection of a known volume of gas into the carrier gas stream. The intensity of the MS signal decreases with increasing carrier gas flow rate, showing a linear dependence, and is not influenced by temperature and amount of analyzed gas. The use of helium as a carrier gas reduces the intensity of the mass spectrometric signal and leads to its broadening. The calibration offers the possibility of quantifying components being present in amounts as small as 0.2-0.5 wt%.