Construction and evaluation of a hermetically sealed accurate ion mobility instrument

Abstract

Ion mobility spectrometry (IMS) is widely used to detect and identify chemical warfare agents, narcotics, and explosives in the field based on their reduced mobility (K 0 ) values. Current detection windows for these analytes can only be as narrow as ±2% of the K 0 values for the analyte being sought. These wide detection windows cause false positive alarms when an interferent with a similar reduced mobility falls within the detection window and triggers an alarm. This results in the loss of time and money as resources are diverted to verify the alarm. A high rate of false positive alarms is caused by a discrepancy in the reported K 0 values across the literature that is, at best, ± 2% of the average available values. By accurately and precisely measuring the variables affecting an ion’s K 0 value, an accurate K 0 value can be produced and the detection windows widths that are established using these reference values can be reduced. Components for accurate analyses have been assembled in the past and here the construction of an accurate ion mobility spectrometry drift tube is described that is accurate to 0.1% of the calculated K 0 value and can be hermetically sealed without inserting the drift tube into a large vacuum chamber. Having a pressure sealed accurate ion mobility spectrometer will allow for the control of the pressure variable within the K 0 equation and the safe analysis of hazardous chemicals. Here the construction of an inexpensive and easily reparable sealed drift tube is described.