A pneumatic sampling switch which can be adapted to the outlet of a thermogravimetric analyzer furnace with a horizontal purge gas flow was developed. This system allows a repetitive introduction of shea sampling pulses of thermogravimetric analyzer evolved gases to a quadrupole mass spectrometric detector. System performance was evaluated through measuring the level of repeatability under different operation conditions. In addition, pulsed sampling thermogravimetry/mass spectrometry introduced no measurable quantitative or qualitative errors. This system can be used for monitoring thermooxidative decomposition reactions, without accelerating the deterioration of quadrupole mass spectrometric detector performance. Furthermore, it can be used as an inlet system for a future on-line TG/GC/MS system.