Ion transmission probability through quadrupole mass filter depending on initial ion condition and rod misalignment

A quadrupole mass filter consists of four equidistant parallel rods. Each opposing rod pair is connected electrically, and direct current (DC) and radio frequency alternating current (AC) potentials are applied between one pair of rods and the other. For specific combinations of AC and DC potentials, only ions with a particular mass-to-charge ratio will have a stable trajectory and pass through the quadrupole. Other ions collide with the rods and are not transmitted. The mass filtering is entirely based on the stability of the trajectory of the ions inside the quadrupole. Despite its simple physical geometry and obvious mass separating principle, it is very difficult to analyze the ion behavior in the device even if there is a small deviation from ideal operating conditions. In this paper, the ion transmission probabilities through a quadrupole were calculated using computer simulation at various initial ion conditions and quadrupole mechanical misalignment. The results of this study mainly show the allowable error for quadrupole design, which can be used in improving the performance of the quadrupole mass filter.