Thermo Scientific TSQ Quantum XLS, Руководство пользователя

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Functional Description
Mass Spectrometer
36 TSQ Quantum XLS Series User Guide Thermo Scientific
Fragmentation efficiency: The fraction of the ion flux at the exit of the collision cell that
results from fragmented ions. Fragmentation efficiency depends directly on the stability of the
ion and indirectly on the mass of the ion. The more stable the ion, the less likely a given
collision will fragment the ion. Typically, low mass ions require a higher collision energy to
dissociate than high mass ions. To compensate for this, you can use the data system to specify
a mass-dependent collision energy ramp.
With a mid-range collision gas pressure, fragmentation efficiency might vary from 15 percent
to 65 percent for various compounds. As the collision gas pressure increases, the
fragmentation efficiency for all compounds approaches 100 percent due to multiple collisions.
The collection efficiency decreases, however, due to scattering.
Overall CID efficiency: The product of the collection efficiency and the fragmentation
efficiency. The overall CID efficiency exhibits a maximum with intermediate pressure. As the
pressure is increased beyond the optimum value, more and more collisions take place, the
probability of scattering increases, and fewer and fewer ions pass through the collision cell.
This results in the collection efficiency decreasing. The fragmentation efficiency also decreases
as the pressure is decreased from its optimum value, because fewer and fewer collisions take
place.
Quadrupole Offset Voltage
The quadrupole offset voltage is a dc potential applied to the quadrupole rods in addition to
the ramping dc voltage. The offset voltage applied to the two rod pairs of the assemblies is
equal in magnitude and equal in sign. Because the quadrupole offset voltage accelerates or
decelerates ions, it sets the TKE of the ions as they enter the quadrupole rod assembly.
In general, for a given experiment, the mass spectrometer has fixed offset voltages for Q1 and
Q2. However, in MS/MS experiments, the quadrupole offset voltage applied to Q3 usually
varies as a scan proceeds. The mass spectrometer automatically computes the Q3 quadrupole
offset voltage necessary and then varies the voltage, as appropriate, as each scan proceeds.
The offset voltage applied to Q2 (which contains the collision cell) is responsible for the
collision energy. The collision energy is the difference in potential between the ion source
(where parent ions are formed) and Q2 (where they collide with collision gas). As the offset
voltage on Q2 increases, the TKE of the parent ions also increases. As a result, increases in the
Q2 offset voltage increase the energy of ion/Ar collisions. The collision energy is usually
ramped downward with
m/z to promote the fragmentation of low mass ions.
Before obtaining any mass spectra, the mass spectrometer tunes Q1 in the Q1MS scan mode
(Q2 and Q3 rf voltage only), and tunes Q3 in the Q3MS scan mode (Q1 and Q2 rf voltage
only). During tuning, the mass spectrometer determines the optimum quadrupole offset
voltage for Q1 and for Q3.