A novel micromachined high-field asymmetric waveform-ion mobility spectrometer

The fabrication and characterization of a novel micromachined high-field as ymmetric waveform-ion mobility spectrometer (FA-IMS) is described. The spec trometer has a 3 x 1 x 0.2 cm(3) rectangular drift tube and a planar electr ode configuration. The planar configuration permits simple construction usi ng microfabrication technology where electrodes and insulating regions are made with deposited metal films on glass substrates. The spectrometer is ch aracterized using organic vapors (including acetone, benzene, and toluene) at ambient pressure and with air as the drift gas. Ions are created in air at ambient pressure using photo-ionization with a 10.6 eV photo discharge l amp (lambda = 116.5 nm). The micromachined FA-IMS exhibited behavior consis tent with conventional FA-IMS designs where compensation voltage was effect ive in discriminating between ion species in high-field radio-frequency (RF ) regimes. Excellent resolution of benzene and acetone ions in mixtures ill ustrates an advantage of the FA-IMS over low-field ion mobility spectrometr y. Detection of toluene at concentrations as low as 100 ppb has been demons trated. Improvements in detection limits, by as much as 100 x, are anticipa ted with improved ionization source designs. The ability to transport both positive and negative ions simultaneously through the FA-IMS drift tube is demonstrated here for the first time. Ion intensity is found to be proporti onal to sample concentration, although clusters of sample ions and neutrals at high concentrations illustrate the need for a drift region which is kep t free of sample neutrals. Micromachining promises cost, size, and power re ductions enabling both laboratory and field instruments. (C) 2000 Elsevier Science S.A. All rights reserved.