Development of an Ion Mobility Spectrometry-Orbitrap Mass Spectrometer Platform

Abstract

Complex samples benefit from multidimensional measurements where higher resolution enables more complete characterization of biological and environmental systems. To address this challenge, we developed a drift tube-based ion mobility spectrometry-Orbitrap mass spectrometer (IMS-Orbitrap MS) platform. To circumvent the time scale disparity between the fast IMS separation and the much slower Orbitrap MS acquisition, we utilized a dual gate and pseudorandom sequences to multiplex the injection of ions and allow operation in signal averaging (SA), single multiplexing (SM), and double multiplexing (DM) IMS modes to optimize the signal-to-noise ratio of the measurements. For the SM measurements, a previously developed algorithm was used to reconstruct the IMS data. A new algorithm was developed for the DM analyses involving a two-step process that first recovers the SM data and then decodes the SM data. The algorithm also performs multiple refining procedures to minimize demultiplexing artifacts. The new IMS-Orbitrap MS platform was demonstrated by the analysis of proteomic and petroleum samples, where the integration of IMS and high mass resolution proved essential for accurate assignment of molecular formulas.

Figure 1.

Top: Schematic diagram of the IMS-Exactive platform. Bottom: Schematic diagram of the scan gate electrodes.

Figure 2.

Timing sequence for the IMS-Orbitrap MS in (a–d) SA, (e–h) SM, and (i–l) DM IMS modes of operation. The delay time, Δt, between the scan gate and the IFT exit gate is stepped to collect an ion mobility spectrum.

Figure 3.

(a) The arrival time distribution of 1+ ions from Pierce calibration mixture utilizing SA mode (see text). The scan gate duration was 200 μs, while the scan gate sweep rate was 200 μs/Orbitrap scan. The m/z values of few ions are annotated. (b) Mass spectrum collected at Orbitrap scan number 92. (c) Mass spectrum collected at Orbitrap scan number 178.

Figure 4.

SM data for a tryptic digest of BSA and Enolase. (a) Multiplexed data for m/z region 820.3–821.2. (b) Demultiplexed data for the same m/z region as (a).

Figure 5.

An example of the DM operation using a 101 multiplexing sequence at the IFT and scan gate. (a) The five time steps correspond to different combinations of the two ion packets’ arrival time and the voltage profile applied to the scan gate. (b) The resulting chromatogram from the application of the five time steps.

Figure 6.

(a) DM encoded data for a selected peak of the heavy gas oil sample. (b) The demultiplexed data after applying the procedure outlined in the Data Processing.

Figure 7.

Selected m/z region for the heavy gas oil sample analyzed in the three IMS modes: (a) SA, (b) SM, and (c) DM.

Figure 8.

IMS-Orbitrap data for a vacuum and hydrotreated gas oil sample. Homologous series are noted on some of the trend lines.

Figure 9.

Trend lines for selected N1 homologous series members.

Figure 10.

(a) 2D IMS-m/z plot of two ions that are partially resolved in (b) the m/z dimension (black solid line) and (c) the mobility dimension. The red and blue dashed lines in (b) represent the m/z peaks selected at drift times of 20.8 and 22.4 ms, respectively.