1
Introduction
Ionization Modes
Thermo Scientific
TSQ Quantum XLS and TSQ Quantum GC User Guide
3
• The mass spectrometer is operated as a tandem mass spectrometer with two stages of mass
analysis. The ion source ionizes the sample and the ion products are mass analyzed by the
first rod assembly. In this case, however, mass-selected ions exiting the first rod assembly
collide with an inert gas in the second rod assembly and fragment to produce a set of ions
known as product ions. (A chamber called the collision cell surrounds the second rod
assembly. The collision cell can be pressurized with an inert gas.) The product ions
undergo further mass analysis in the third rod assembly to detect selected ions. Two stages
of mass analysis yield far greater chemical specificity than a single stage can achieve,
because of the system’s ability to select and determine two discrete but directly related sets
of masses.
In a first stage of mass analysis the mass spectrometer can be used to elucidate the structures of
pure organic compounds and the structures of the components within mixtures. Furthermore,
in a second stage of mass analysis, the mass spectrometer can fragment and separate each ionic
fragment of a molecule formed in the ion source to build up an entire structure for the
molecule, piece by piece. Thus, TSQ Quantum XLS and TSQ Quantum GC systems make
investigating all pathways for the formation and fragmentation of each ion in the mass
spectrum possible.
The two stages of mass analysis, with resultant reduction of chemical noise in the final mass
spectrum, allow for very selective and sensitive analysis.
Each sequence of single or triple-stage mass analysis of the ions is called a scan. The mass
spectrometer uses several different scan modes and different scan types to filter, fragment, or
transmit ions in the mass analyzer. Along with the ionization and ion polarity modes, the
ability to vary the scan mode and scan type affords the user great flexibility in the
instrumentation for solving complex analytical problems.
Ionization Modes
The specific process used to ionize the analyte is referred to as the ionization mode. You can
operate the TSQ Quantum XLS and TSQ Quantum GC mass spectrometers in either of two
ionization modes:
• Electron ionization mode
• Chemical ionization mode
1
The instrument can also be used as a single-stage mass spectrometer by transmitting the ions through the first
and second rod assemblies followed by mass analysis in the third rod assembly.