A mass spectrometer and method for operating the same. The mass spectrometer includes a vacuum chamber and an input port that receives ions to be analyzed in the mass spectrometer. The chamber is adapted to operate at a pressure less than a first pressure, and includes a wall that separates the chamber from an environment outside the chamber at atmospheric pressure. The input port provides a pressure drop between the outside environment at a second pressure and the chamber. The input port includes a plurality of channels, each channel having first and second electrodes arranged on opposing surfaces of that channel and having first and second ends. The first end of each channel is at a pressure equal to the first pressure and the second end is at a pressure less than the second pressure.