Abstract: An ion mobility detector is disclosed having a drift tube of non-electrically conductive material and a series of spaced conductive rings disposed upon the exterior surface of the tube. An adjustable high voltage source is provided to apply voltages to the rings to establish a potential gradient along the drift tube. The detector further includes a reaction region separated from the drift tube by an injection gate. The ratio of the width of the conductive rings to their thickness is at least 2.1 and the ratio of the internal diameter of the drift tube to the maximum transverse dimension of the injection gate also is at least 2:1.