The effects of pulsed introduction of buffer gas on ion storage and detection efficiencies in a quadrupole ion trap

The quadrupole ion trap is commonly operated with a constant background pressure of an inert, low molecular weight buffer gas. This inclusion of a buffer gas has been shown to increase the sensitivity and mass resolution of the instrument. Research to gain an understanding of these effects, both experimental and through simulations, has typically assumed that it is optimal to maintain a constant buffer gas pressure throughout the entire experiment This article describes the effects of the pulsed introduction of buffer gas at strategic points within the analytical scan and evaluates those events during which the presence of buffer gas is critical. By incorporating a pulsed valve within the ion trap manifold, both the presence and pressure of the buffer gas can be controlled and varied during the individual steps of the scan. The presence of helium buffer gas just before the ion ejection and detection event showed a greater increase in intensity of the ion signal than at any other time in the analytical scan. In addition, this increase in intensity upon pulsed introduction of buffer gas prior to detection is constant over a wide range of pulsed valve open times (i.e., pressures), whereas the signal enhancement upon pulsed introduction of the buffer gas before ionization is observed only over a narrow range of pulsed valve open times.