Chapter 2: Mass Cytometry and CyTOF XT
CyTOF XT System Components Overview
CyTOF XT User Guide
35
High-Pass Ion Optics
The ion cloud leaving the vacuum interface is dominated by low mass argon (Ar) ions from
the plasma. These ions are not of analytical interest and are of such high abundance that
they may quickly damage the detector. To remove them, the beam is focused and directed
into the high-pass ion optics. High-mass ions are guided through this pathway, and as a
result, a stream of ions (corresponding to individual cells) that contain only the high-mass
isotopic probes exits the high-pass ion optics.
Figure 26. The high-pass ion optics remove unwanted low-mass argon and other ions from the ion
beam, transmitting clouds that contain ions of high mass (>75 amu) to the TOF analyzer.
Time-of-Flight Mass Analyzer
The ion clouds that exit the high-pass ion optics consist of a mixture of high-atomic-weight
probes in a randomly distributed array. These ions are sent to the time-of-flight (TOF) mass
analyzer, which separates the ions in time based on the mass-to-charge ratio.
Figure 27. Separation of ions in the TOF analyzer. Ion clouds are subjected to an electrostatic force,
which orthogonally accelerates the incoming ions toward the detector. As a result, the ions separate
based on their mass-to-charge ratio, with lighter elements reaching the detector first.
The beam exiting the high-pass ion optics enters through the entrance slit into the
accelerator chamber of the TOF analyzer. At 13 µs intervals (frequency of 76.8 kHz), a pulse
of several hundred volts is applied to the push-out plate, accelerating a packet of ions
orthogonally toward the reflector, which redirects the ions toward the detector. The electric
fields in the accelerator and reflector are configured to focus ions into tight time-resolved
