A specially constructed helium flushed probe system was developed in order to ensure a quick transport of species extracted from a process gas at a few tens of mbar to a quadrupole mass spectrometer. The amount of extracted process gas can be adjusted by the setting of the helium gas flow. The time response of the probe system was simulated and compared with measurements performed on a pulsed hydrogen-deuterium discharge. The probe system is characterized by a delay time of a few tens of ms depending on the process pressure and a time resolution of about 20 ms. A decrease of the time resolution to values well below 10 ms is possible.