Ion Detection Systems; Figure 21. Visual Representation Of Mass Analyzer Operation - Thermo Scientific LTQ Series Hardware Manual

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Functional Description
Mass Spectrometer

Ion Detection Systems

26 LTQ Series Hardware Manual

Figure 21. Visual representation of mass analyzer operation

The Velos Pro mass spectrometer operates in a slightly different manner. The LXQ and
LTQ XL mass spectrometers perform all four steps in one trap, but the Velos Pro does not. In
the Velos Pro, the scan-out step can only occur in the trap with the electron multipliers, which
is the low pressure trap, while initial trapping, isolation, and dissociation of the ions occur in
the high pressure trap.
The LTQ Series mass spectrometer has a high-sensitivity, off-axis ion detection system. The
LXQ has one electron multiplier, and the LTQ XL and Velos Pro have two detectors. The ion
detection system produces a high
switching between positive ion and negative ion modes of operation. The electron multipliers
are located on opposite sides of the mass analyzer. Each electron multiplier has a
corresponding conversion
A conversion dynode is a concave metal surface located at a right angle to the ion beam
(Figure 21). A high positive potential (15 kV) for negative-ion detection or a high negative
potential (–15 kV) for positive-ion detection is applied to the conversion dynode. For the
LTQ XL and the Velos Pro mass spectrometers, both conversion dynodes are physically
connected and operate at the same voltage. An ion striking the surface of the conversion
dynode produces one or more secondary particles. The curved surface of the conversion
dynode focuses these secondary particles and the voltage gradient accelerates them into the
electron multiplier. The conversion dynode shields shield the vacuum manifold from the
electric field that the conversion dynode produces.
signal-to-noise ratio (S/N)
dynode.
Dynode in the
ion detection
system
and enables voltage polarity
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