CONTINUOUS DETECTION OF TOXIC VAPORS USING A FIELD DOMAIN ION MOBILITY SPECTROMETER.

THE MOTION OF A CHARGED MOLECULE THROUGH A CLOUD OF NEUTRAL MOLECULES UNDER THE INFLUENCE OF AN ELECTRIC FIELD CAN BE USED TO SEPARATE AND IDENTIFY CHARGED SPECIES BY VIRTUE OF THE DIFFERENCES IN COLLISION CROSS-SECTIONS AND CHARGE QUANTITIES AMONG OTHER CHARGED MOLECULES. THE CHARACTERISTIC USED TO IDENTIFY THE MOLECULE (IN ITS CHARGEDFORM) IS ITS ELECTRIC MOBILITY. THE TECHNIQUE EMPLOYING THIS CHARACTERISTIC TO IDENTIFY MOLECULES IS ION MOBILITY SPECTROMETRY (IMS), WHICH HAS BEEN UNDER DEVELOPMENT FOR ABOUT THE PAST 18 YEARS. THE TECHNIQUE IS EXTREMELY SENSITIVE, BEING CAPABLE OF DETECTING COMPOUNDS IN THE LOW PARTS-PER-BILLION AND HIGH PARTS-PER-TRILLION CONCENTRATION RANGE, AND DOING SO AT ATMOSPHERIC PRESSURE. THE CONVENTIONAL IMS IS ESSENTIALLY A TIME-OF-FLIGHT SPECTROMETER FOR IONS IN AN ATMOSPHERIC PRESSURE NEUTRAL GAS. A NEW METHOD IS PROPOSED WHEREBY, INSTEAD OF MEASURINGTIME-OF-FLIGHT, A RETARDING ELECTRIC FIELD IS USED TO STOP AN ION FROM REACHING THE COLLECTOR IN A STREAMING GAS MIXTURE WHICH IS USED TO CHARACTERIZE THE ION. THE LOWER THE MOBILITY OF AN ION, THE HIGHER IS THE FIELD REQUIRED TO ACCELERATE IT IN OPPOSITION TO THE FLOW DIRECTION. IT WILL BE DEMONSTRATED IN THE PROPOSED RESEARCH THAT A FIELD-DOMAINION MOBILITY SPECTROMETER CAN BE DEVELOPED WHICH WILL BE SMALLER, SIMPLER, FASTER, AND LESS POWER CONSUMING THAN THE CONVENTIONAL TIME-DOMAIN ION MOBILITY SPECTROMETER, SO THAT A COMPACT PORTABLE CONTINUOUS MONITORING INSTRUMENT CAN BE EVOLVED.