Yale DMA-MS Facility
Yale’s open facility on ion mobility spectrometry/mass spectrometry (IMS-MS)
An operational IMS-MS facility with excellent resolving power (50 for IMS, 104 for MS), >50% transmission through the IMS, and high mass range (~ 40,000 m/z) is available at Yale thanks to the loan of a QSTAR XL Mass spectrometer (MS) and a Differential mobility analyzer (DMA) from the manufacturers Applied Biosystems and SEADM.
The DMA is a peculiar IMS device combining a flow field U and an electric field E between two parallel plates. It disperses a beam of ions into a fan, such that only the ions with a well defined electrical mobility are transmitted into an outlet slit leading to the MS inlet. The main advantage of the DMA over other more familiar IMS instruments is the simplicity of its integration as a front-end into a preexisting MS with an atmospheric pressure source. The integration to form a DMA-MS instrument requires essentially no change in the vacuum system of the MS. The DMA measures true mobility, generally in air, N2 or CO2). Yale’s DMA-MS facility includes an Electrospray (ES) source, but no chromatography. Samples need therefore to be pre-purified. The DMA is also unique in enabling mobility determination of ions as produced by the ES source, without the structural modifications that tend to arise when an ion crosses a vacuum interface, an ion guide, or is injected into a drift cell.
Figure 1: Operation of the differential mobility Analyzer (DMA). Ions are fed through a slit on the upper plate, and dispersed into a fan by combined fluid flow (rightwards) and electric (downwards) fields. Ions of a pre-selected electrical mobility are drawn through an exit hole into the mass spectrometer.
Examples of DMA-MS spectra obtained, and related scientific results:
The DMA-MS facility is open for use by visitors, primarily for scientific experiments involving high molecular weight species, with a special interest in biopolymers (widely interpreted). Potentially interested visitors should contact email@example.com (1-203-432-4347). No Yale funds are available to run external samples or to support visits. What we offer is a welcoming environment, a functional machine, instruction on how to run it, the assistance of graduate student Rafael Borrajo (who runs the instrument for our own research program), and some experience about electrosprays. The instrument is located at Yale's Keck Facility (under the Directorship of Prof. Kenneth Williams), where there are plenty of expert colleagues doing their own work, and with whom there will be informal chances to interact. One week visits generally suffice to collect large data sets. Longer visits may take place if appropriate. Particularly promising mailed samples may exceptionally be run free of charge. Interested visitors may receive free use (for one year) of the commercial software required for data analysis back at their own institution.