A quadrupole mass filter with flat electrodes

The potential distribution produced by a flat-plate quadrupole system is examined by computer simulation. The width and spacing of the electrodes is varied to determine the geometry which gives the best approximation to the ideal, hyperbolic case. Over a significant central region the potentials match to better than 0.1%. This best case has a width-to-spacing ratio of 0.453 and electrodes are placed at a distance 1.6% greater than the spacing of the hyberbolae being simulated. A chart recording of a practical flat-plate quadrupole confirms that such a system is capable of mass filtration. (Auth.)