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
where:
- 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 Type | Principle of Analysis |
|---|---|---|
| 1. | Magnetic sector | Deflection of ions in a magnetic field. Ion trajectories depend on m/z value |
| 2. | Double-focusing | Electrostatic focusing followed by magnetic field deflection. Trajectories depend on m/z values. |
| 3. | Quadrupole | Ion motion in dc and radio-frequency fields. Only certain m/z values are passed. |
| 4. | Ion Trap | Storage 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 resonance | Trapping 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-flight | Equal 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