2
Functional Description
MS Detector
28
Surveyor MSQ Plus Hardware Manual
Thermo Scientific
Figure 19.
Schematic of the RF/dc prefilter, mass analyzer, and ion detector
Ion Detection System
The Surveyor MSQ Plus MS detector is equipped with a high sensitivity, off-axis ion
detection system that produces a high signal-to-noise ratio and allows for voltage polarity
switching between positive ion and negative ion modes of operation. The ion detection
system includes a 10 kV conversion dynode and a channel electron multiplier. The ion
detection system is located at the rear of the vacuum manifold behind the mass analyzer. See
The conversion dynode is a concave metal surface that is located at a right angle to the ion
beam. A potential of +10 kV for negative ion detection or -10 kV for positive ion detection is
applied to the conversion dynode. When an ion strikes the surface of the conversion dynode,
one or more secondary particles are produced. These secondary particles can include positive
ions, negative ions, electrons, and neutrals. When positive ions strike a negatively charged
conversion dynode, the secondary particles of interest are negative ions and electrons. When
negative ions strike a positively charged conversion dynode, the secondary particles of interest
are positive ions. These secondary particles are focused by the curved surface of the conversion
Source
entrance
cone
M-Path
Source
extraction
cone
Square
quadrupole
RF/dc prefilter
Quadrupole
mass analyzer
Ion
detector
Forepump
Split flow
turbomolecular pump
Unbounded, neutralized ions
being pumped away by the
vacuum system
Bounded ions successfully
transmitted by the mass
analyzer reaching ion detector
