Thermo Scientific TSQ Series Hardware Manual page 47

2
Functional Description
Mass Spectrometer
Figure 26. Collision cell (top), Q2 quadrupole (bottom), and lenses
Lenses L21, L22, Lenses L31, L32,
and L23 and L33
RF and DC Fields Applied to the Quadrupoles
In a quadrupole rod assembly, because rods opposite each other in the array connect electrically,
the four rods can be considered as two pairs of two rods each. Ac and dc voltages are applied to the
rods and these voltages are ramped during the scan. Voltages of the same amplitude and sign are
applied to the rods of each pair. However, the voltages applied to the different rod pairs are equal in
amplitude but opposite in sign. See Figure 27.
Figure 27. Polarity of the RF and dc voltages applied to the rods of the Q1 and Q3 mass analyzers
RF voltage
+ dc voltage
RF voltage 180° out of phase
– dc voltage
The ac voltage applied to the quadrupole rods is of constant frequency (1.123 MHz). The RF
voltage applied to the rods varies from 0 to 10000 V peak-to-peak, and the dc voltage varies from
0 to ±840 V. Voltages of the same amplitude and sign are applied to each rod pair. However, the
voltages applied to the other rod pair are equal in amplitude but opposite in sign.
Because the frequency of this ac voltage is in the radio frequency range, it is referred to as rf voltage.
In Figure 28, the solid line represents the combined rf and dc voltage applied to one rod pair, and
the dashed line represents the combined rf and dc voltage applied to the other rod pair. The ratio
of rf voltage to dc voltage determines the ability of the mass spectrometer to separate ions of
different mass-to-charge ratios.
Thermo Scientific TSQ Series Hardware Manual 29