Ion Mobility Spectrometry

Concomitantly with our efforts in the field of ambient MS, we have systematically pursued the goal of developing ultrahigh resolution atmospheric pressure DTIMS instrumentation for portable field detection applications. We started in 2004 by designing and building (in collaboration with TOFWERK AG) the first nanoelectrospray ionization DTIMS spectrometer completely constructed in resistive glass. This new H2-reduced lead silicate material (provided by Burle, now Photonis Inc.) enabled the creation of a highly homogeneous electric field within the drift region of the instrument, leading to very high resolving power (RFWHM»90) in a short (25 cm) drift tube equipped with a Faraday plate detector [1]. This instrument was not only much simpler to build than typical stacked-ring electrode designs, but it was also more affordable and safer, as no extensive machining and external voltage divider were required. In follow up work we introduced a new “digital multiplexing” method to increase DTIMS duty cycle. Using arbitrary modified pseudorandom pulse sequences, we increased the duty cycle up to 50%, with a gain in signal-to-noise ratio of up to 6-fold, simultaneously eliminating typical “echoes” observed in Hadamard multiplexing approaches [2]. In theoretical studies published in 2010 we fitted peak width data to a semi-empirical model developed to study non-ideal contributions to resolving power. Results showed that the achievable resolution could be still increased by at least 50% by improving the Bradbury-Nielsen gating system and detector assembly design [3]. These improvements would not be realized until 2012, when we partnered with Photonis to build a better engineered version of our instrument which was released at Pittcon 2013 (http://www.photonis.com/en/content/301-dart-ion-mobility-spectrometer). The implementation of a new photoetched ion gate resulted in resolving power of up to 160 for test compounds on a routine basis. This new instrument, not only utilizes resistive glass technology, but it also incorporates an ambient plasma DART ion source based on a new type of transmission mode and secondary ionization interfaces [4].
 
 
(1)       M. Kwasnik, K. Fuhrer, M. Gonin, K. Barbeau, F. M. Fernandez; "Performance, resolving power, and radial ion distributions of a prototype nanoelectrospray ionization resistive glass atmospheric pressure ion mobility spectrometer". Anal. Chem. 79, 7782-7791 (2007).doi: 10.1021/ac071226o
(2)       M. Kwasnik, J. Caramore, F. M. Fernandez; "Digitally-multiplexed nanoelectrospray ionization atmospheric pressure drift tube ion mobility spectrometry". Anal. Chem. 81, 1587-1594 (2009).doi: Doi 10.1021/Ac802383k
(3)       M. Kwasnik, F. M. Fernandez; "Theoretical and experimental study of the achievable separation power in resistive-glass atmospheric pressure ion mobility spectrometry". Rapid Commun. Mass Spectrom. 24, 1911-1918 (2010).doi: 10.1002/rcm.4592
(4)       G. A. Harris, M. Kwasnik, F. M. Fernandez; "Direct analysis in real time coupled to multiplexed drift tube ion mobility spectrometry for detecting toxic chemicals". Analytical Chemistry 83, 1908-1915 (2011).doi: 10.1021/ac102246h