# Improving the Quadrupole to Ion Mobility Region in a Digital Quadrupole/Ion Mobility/Orbitrap Mass Spectrometer

## TL;DR

The paper describes modifications to a mass spectrometer to improve ion mobility and isolation of large protein complexes.

## Contribution

The novel contribution is the addition of vacuum regions to enhance ion isolation and transfer efficiency in a digital quadrupole/ion mobility/Orbitrap instrument.

## Key findings

- Isolation of a single charge state of C-reactive protein (m/z 5,000) was successfully demonstrated.
- Fourier transform ion mobility spectra were acquired in both full scan and isolation modes.
- Optimized ion optic voltages minimized ion heating for helium and nitrogen bath gases.

## Abstract

A quadrupole/drift tube ion mobility/Orbitrap instrument
requires
pumping from atmosphere to 10–5 Torr in the quadrupole
analyzer region, back to 1 Torr for the drift tube, and a return to
10–5 Torr for the Orbitrap high vacuum region. The
Orbitrap high vacuum region contains the transfer multipole, C-trap,
and HCD cell. Insufficient pumping between the drift tube and quadrupole
leads to helium in the quadrupole analyzer chamber which compromises
performance. Additional vacuum regions were added between the drift
tube and the analyzer chamber to maintain the analyzer pressure below
5.5 × 10–5 Torr with the drift tube pressurized
to 1.5 Torr of He. In this configuration, the isolation of a single
charge state of C-reactive protein (m/z 5,000) was demonstrated. Fourier transform ion mobility spectra
were acquired with the quadrupole in full scan mode and in the isolation
mode. Ion optic voltages were optimized for both helium and nitrogen
bath gases in the drift tube so that minimal ion heating was observed
entering the drift tube. These instrument modifications enable improved
ion transfer efficiency, allowing for better ion isolation by the
digital quadrupole ion mobility separation of large protein complexes,
as illustrated by the 23+ and 24+ charge states of C-reactive protein.