The concept of the helical dipole conduit and its applications

Abstract

A tubular ion conduit has been constructed, which transports ions by convection by means of a carrier gas. Typical inlet pressures are in the 10–100 mbar range, with outlet pressures as low as 10 −3 mbar. The 20–30 cm long, 1–2 mm inner diameter capillary tube, made of an electrically insulating material, is surrounded by a specially configured pair of helical electrodes (“helical dipole”) which are supplied with symmetrical voltages in the tens of volts amplitude and in 1 MHz frequency range. The vibrational average force field generated reduces the tendency of ions to hit the inner wall of the tube. This way ions can be transported with minimal loss. Presently known ion guides are operated under molecular flow (high vacuum) conditions only, as opposed to the method described here, where the carrier gas enters under viscous flow conditions and exits as molecular flow. In addition, existing ion guides are stiff in contrast to the flexible construction described here which can be easily and inexpensively manufactured. The new ion conduit is expected to have important applications in connecting ambient or near-ambient pressure electrospray ionization or atmospheric pressure ionization-type ion sources to mass spectrometers, while reducing pumping requirements, e.g. field portable equipment. Furthermore, the device may provide a means for connecting electron multiplier detectors to near ambient pressure analyzers such as ion mobility spectrometers.