A mass analyzer is used to distinguish minute mass differences while allowing a sufficient number of ions to pass through to produce measurable ion currents.

Resolution of Mass Spectrometers

Resolution is defined as the capacity of a mass spectrometer to differentiate between masses. It is defined as:

R= m/△m


  • m= the nominal mass of the peak with the lowest mass.
  • △m is the mass difference between two adjacent peaks.

Table of Common Mass Analyzers for Mass Spectrometry

S.No.Analyzers TypePrinciple of Analysis
1.Magnetic sectorDeflection of ions in a magnetic field. Ion trajectories depend on m/z value
2.Double-focusingElectrostatic focusing followed by magnetic field deflection. Trajectories depend on m/z values.
3.QuadrupoleIon motion in dc and radio-frequency fields. Only certain m/z values are passed.
4.Ion TrapStorage of ions in space defined by the ring and end cap electrodes. The electric field sequentially ejects ions of increasing m/z values.
5.Ion Cyclotron resonanceTrapping of ions in the cubic cell under influence of trapping voltage and magnetic field. Orbital frequency related inversely to m/z value
6.Time-of-flightEqual kinetic energy ions enter the drift tube. Drift velocity and thus arrival time at the detector depend on mass.

Reference: Fundamentals of Analytical Chemistry By Douglas A. Skoog, Donald M. West, F. James Holler, Stanley R. Crouch · 2013

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