Atmospheric flow tube-mass spectrometry (AFT-MS) first emerged in 2012 as an ambient vapor sampling technique developed by Ewing et al. and applied to the sensing of trace quantities of RDX molecules clustered with nitrate ions. This iteration of AFT-MS used selected-ion monitoring (SIM) during analysis via a triple-quadrupole mass spectrometer and subsequently has been applied to vapor analysis of other explosives adducted with nitrate as well as positively-charged organophosphorus species clustered with amines as proton-bound dimers. Building upon these initial AFT-MS experiments, we have recently applied the atmospheric flow tube ionization method to the detection of alkylphosphonic acids from methanol solution headspace and adducted with nitrate and nitrate-nitric acid species via linear ion trap mass spectrometry. This was performed in an effort not only to demonstrate the application of ion trap MS systems with AFT-MS, but also to characterize the gas-phase ion chemistry of a homologous series of alkylphosphonic acids including methylphosphonic acid (MPA), which is an environmental pollutant and hydrolysis product of some chemical agents. Our article, “Characterization of Alkylphosphonic Acid Vapors Using Atmospheric Flow Tube-Ion Trap Mass Spectrometry,” can be found in Rapid Communications in Mass Spectrometry.
Following up on previous post, we’ve finally released a major update to the Open Source IMS Initiative. Appearing now in Hardware X we detail a new modular IMS design that is extremely flexible. Three of our ASMS 2018 posters feature data from these system and the are proving an invaluable new tool to our research infrastucture. Though the current systems are limited to lower temperature operation (i.e < 120 °C), the designs are readily adapted to Rogers material which is quite robust well above 200 °C. Another key adaptation making this design tractable is the new ion shutter design which uses 3 grids to create a set of well defined ion pulses. Though the BN-gates are attractive in that the physical structure is in a single plane, their construction is an art. Moreover, the fields established by the BN gates are also, by no means, fully planar. With the new design we can achieve that smooth field in the region surrounding the ion gate and still get extremely small ion gate pulse widths (i.e < 20 μs). If you are interested in some of the core details or have suggestions for improvement, come find us on github: https://github.com/bhclowers/OS-IMS
Ion gating remains a critical aspect of drift tube IMS experiment and a range of clever approaches have been used the past. However, most techniques use a physical grid to modulate the ion beam. In collaboration with Steve Kenyon and Keith Gendreau we’ve adapted a modulated x-ray source to printed circuit board IMS. Though there is still room for improvement, the initial results look quite promising. Interestingly, because the source is now located orthogonal to the drift axis, a new term is added to the descriptors of peak width. What we’re most excited about, however, is the fact that because we no longer have a physical ion gate, some of the capacitive coupling during the pulsing of a standard ion gate is now effectively eliminated–enter artifact-free multiplexing…
Outside of an ionization source and a Faraday plate, a drift tube IMS system is fundamentally comprised of 5 primary components:
- Reaction/Drift Cell
- Ion Gate
- Gate Pulsing Electronics
- Current to Voltage Converter
- Data Acquisition System (DAQ)
Within the IMS research community hardware and DAQ solutions are often custom and rarely replicated exactly. In an effort to address this knowledge and resource gap, the links posted below outline a range of solutions to the construction and operation of research-grade ion mobility spectrometers. It is our sincere hope that this information will be useful to other research groups and encourage others to make suggestions and improvements. The github links, including those from GAA Custom Engineering are found below:
Ion Gate Pulser
Current to Voltage Converter
WiPy DAQ System and GUI
The most recent poster presented ISIMS 2016 in Boston, MA can be found here: Clowers_ISIMS_2016_v5.
We are pleased to report the publication of our work outlining the effective coupling of a drift tube IMS system with an ion trap mass spectrometer. Compared to previous implementations (see our 2005 publication) we have dramatically improved the IMS duty cycle by encoding the mobility information in the frequency domain. Using this Fourier approach we can cover the full mobility spectrum in a fraction of the time that is typically required for a signal averaging technique. Perhaps most impressive from our perspective, is the ease of implementation. It is truly plug ‘N play with no hardware synchronization required. If anyone is interesting in more details regarding the pulsing hardware and parameters, you know where to find us.
Abstract: Historically, high pressure ion mobility drift tubes have suffered from low ion duty cycles and this problem is magnified when such instrumentation is coupled with ion trap mass spectrometers. To significantly alleviate these issues, we outline the result from coupling an atmospheric pressure, dual-gate drift tube ion mobility spectrometer (IMS) to a linear ion trap mass spectrometer (LIT-MS) via modulation of the ion beam with a linear frequency chirp. The time-domain ion current, once Fourier transformed, reveals a standard ion mobility drift spectrum that corresponds to the standard mode of mobility analysis. By multiplexing the ion beam, it is possible to successfully obtain drift time spectra for an assortment of simple peptide and protein mixtures using an LIT-MS while showing improved signal intensity versus the more common signal averaging technique. Explored here are the effects of maximum injection time, solution concentration, total experiment time, and frequency swept on signal-to-noise ratios (SNRs) and resolving power. Increased inject time, concentration, and experiment time all generally led to an improvement in SNR, while a greater frequency swept increases the resolving power at the expense of SNR. Overall, chirp multiplexing of a dual-gate IMS system coupled to an LIT-MS improves ion transmission, lowers analyte detection limits, and improves spectral quality.
We are pleased to announce the unpacking and, more importantly, the successful pump down of the G2. Combined with a new UPLC unit we anticipate this instrument playing a large role in future metabolomics work in our laboratory. Kudos to Justin Chang from Waters for executing the pump down sequence like a champ.
Unboxing to commence in t-minus 6 days and counting…
Comparison of CID and UV Photodissociation of Leucine Enkephaline Acquired at WSU.
In early 2015 the research group is pleased to bring the next generation ion mobility-ion trap system online. This system is equipped with two ion gates which allows the speed of the IMS to be effectively coupled to the slow scan speeds of traditional ion trapping experiments. Though not as fast as tradition IMS-TOF configurations, this experimental setup does allow multiple stages of CID and alternative modes of fragmentation such as UV and IRMPD. Another unique feature of this IMS system is that it can obtain IMS spectra using a standard Faraday plate and/or the LTQ.
Additional photos of the initial setup and UV beam line:
The ExcellIMS Dual Gate System smoothly mates to the LTQ.
Though a little difficult to see the IMS tube actually uses a square drift tube design with a nice set of BN gates.
Fully functional Dual-Gate IM-LTQ system.
193 nm Excimer Beam Line