Selective Ionization and Separation in Ion Mobility Spectrometry

Abstract

Ion Mobility Spectrometry (IMS) provides reliable and fast detection in a multitude of worldwide environments including security and pharmaceutical applications where the ability to rapidly detect explosives and narcotics provides an invaluable tool. However; drawbacks such as low resolving power and high false positive rates hinder the full capability of the IMS system for detection of harmful chemicals. The work described herein demonstrates modifications of the IMS experimental techniques leading to novel methods for use of IMS in both homeland security and pharmaceutical applications.Several ionization source techniques, including 63Ni, corona, electrospray and desorption electrospray, were utilized in both homeland security and pharmaceutical applications to modify IMS instrumentation for selective ionization capabilities. An IMS system was designed and built with the goal to achieve a lightweight modular design offering high performance for the detection of trace explosives using corona ionization, a safer option to 63Ni ionization sources. The potential of electrospray ion mobility-mass spectrometry (ESI-IMMS) as a method for monitoring pharmaceutical reactions in real time was demonstrated with a reductive amination reaction and real time data were collected on the timescale of 300 seconds. Desorption electrospray ionization (DESI) was coupled to an atmospheric pressure IMS for the direct analysis of active ingredients formulated into pharmaceutical samples. Increased selectivity for drug responses over excipient responses was demonstrated through the use of a doping agent in the DESI solvent. Additionally, the use of a modifier in the drift gas of an ion mobility spectrometer as a secondary method to lower the false alarm rate of current IMS systems was demonstrated. An analytical method that utilizes structure selective ion molecule interactions (SSIMI) in ion mobility spectrometry to shift the mobility of a targeted analyte through the addition of a gas phase modifier to the buffer was developed to selectively change the separation of target analytes. A modifier with a proton affinity similar to the target analyte produced the greatest changes in mobility due to the formation of a cluster between the neutral modifier and target analyte ion.