ABSTRACT
A prototype is introduced based on the transversal modulation ion mobility spectrometry (TMIMS) technique, which provides a continuous output of mobility-selected ions, greatly easing the synchronization between different analyzing stages. In the new architecture, two stages of filtration are used to drastically reduce the background produced by one stage alone. Two-stages TMIMS was coupled with two different atmospheric pressure interface mass spectrometers (MS). The new system enables IMS-IMS-MS analysis and other modes of operation: IMS prefiltration, IMS-IMS, and full transmission mode. It provides a resolving power R > 60 in IMS mode, and R > 40 in each stage of IMS-IMS mode. 2-Propanol vapors were introduced in one of the stages to enhance the mobility variations, and their effect was studied on a set of tetraalkylammonium ions. We found that concentrations as low as 1% (in partial pressure) produce mobility variations as high as 20%, which suggest that IMS-IMS separation using dried N2 (in one stage) and a dopant (in the other stage), could be a very powerful way to enhance the separation capacity of the IMS-IMS prefiltration approach.
Subject(s)
Mass Spectrometry/instrumentation , 2-Propanol/chemistry , Ammonium Compounds/chemistry , Equipment Design , Ions/chemistryABSTRACT
In secondary electrospray ionization (SESI) systems, gaseous analytes exposed to an elecrospray plume become ionized after charge is transferred from the charging electrosprayed particles to the sample species. Current SESI systems have shown a certain potential. However, their ionization efficiency is limited by space charge repulsion and by the high sample flows required to prevent vapor dilution. As a result, they have a poor conversion ratio of vapor into ions. We have developed and tested a new SESI configuration, termed low-flow SESI, that permits the reduction of the required sample flows. Although the ion to vapor concentration ratio is limited, the ionic flow to sample vapor flow ratio theoretically is not. The new ionizer is coupled to a planar differential mobility analyzer (DMA) and requires only 0.2 lpm of vapor sample flow to produce 3.5 lpm of ionic flow. The achieved ionization efficiency is 1/700 (one ion for every 700 molecules) for TNT and, thus, compared with previous SESI ionizers coupled with atmospheric pressure ionization-mass spectrometry (API-MS) (Mesonero, E.; Sillero, J. A.; Hernández, M.; Fernandez de la Mora, J. Philadelphia PA, 2009) has been improved by a large factor of at least 50-100 (our measurements indicate 70). The new ionizer coupled with the planar DMA and a triple quadrupole mass spectrometer (ABSciex API5000) requires only 20 fg (50 million molecules) to produce a discernible signal after mobility and MS(2) analysis.
ABSTRACT
The analysis of ions according to their mobility is a technique that is attracting increasing interest. The new technology presented here, which we have termed Transversal Modulation Ion Mobility Spectrometry (TM-IMS), utilizes only electric fields, operates at atmospheric pressure, produces a continuous output of mobility selected ions (according to their true mobility and not to nonlinear effects), and has a very accessible inlet and outlet. These features would make it an ideal choice for tandem IMS-MS analysis in combination with most commercial Atmospheric Pressure Interface MS (API-MS) systems. We modeled and evaluated two different TM-IMS configurations (TM-IMS, and multistage TM-IMS), and we concluded that the most promising configuration would be a two-stage TM-IMS. We developed and tested a TM-IMS, and the measured resolving power is R = 55. The TM-IMS behaves similarly to the planar Differential Mobility Analyzer, but the TM-IMS utilizes only electric fields, and no fragile flow with high Reynolds numbers is required. We tested the robustness of the TM-IMS, which proves to be a very robust and reliable analyzer: the required voltage accuracy is 5 V in 10 kV, and the mechanical precision is 1 mm in 5 cm.
