Technical Description: System
Mass Analyser
Thermo Fisher Scientific
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
B-9
Refer to
For a given magnetic field (i.e. a given magnet current), only ions of
a specific mass to charge ratio will reach the mass spectrometers
collector. Masses that are lighter than that for which the instrument
has been tuned will be deflected more and masses that are heavier
deflected less. Therefore, the higher the mass of ions to be detected
the higher the magnetic field and consequently the higher the magnet
current.
H
I
m
Equation 5.
Where:
I
m
= magnet current
H = field created by the electromagnet
Figure B
–6.
Separation of ions through the magnetic sector
Two detectors are available in the collector assembly (the Faraday
detector and the optional MCP, the operation of which are described
below.
In conventional sector mass spectrometers, compensation for errors
in analyser geometry, magnet fringing field effects and beam
aberrations, resulting from localized, contamination induced charge
effects is achieved by adjusting the magnet position. In the
Prima PRO instrument, this is addressed by fixing the position of the
magnet and using a quad lens positioned before the collector to
compensate for and adjust the position of the refocused beam image.
This lens is capable of producing either a converging or diverging
beam profile as required to adjust the effective focal length of the
instrument and thereby trim minor changes electronically. The
Mass
Analyser
Collector
