There are several types of analyzers used for analyzing the mass to charge (m/z) ratio of ions created in the source, these analyzers can also be combined to form tandem mass spectrometers. When multiple types of analyzers are combined, they are called hybrid instruments. Below are simplistic explanation of the types of analyzers with their advantages and disadvantages.
Magnetic Sector Instruments- Sector type instruments are made of electric and magnetic fields that bend a beam of ions travelling at relatively high energies. They were once the most popular analyzer for high resolution analysis, but have gone out of favor because a lack of sensitivity when scanning, the space required and the complexity of actually running them. One area that it is still being used is dioxin analysis, because of its high sensitivity in a high resolution selected ion monitoring (SIM) mode. SIM is setting the instrument to a specific mass and monitoring that one mass as a function of time to create a chromatogram of the chemical.
Quadrupole mass spectrometers - Quadrupole mass spectrometers are probably the most common mass spectrometers, because of the simplicity to use, sensitivity, and quick scan speeds. These properties makes them ideal for such applications as GC-MS and LC-MS. It is basically 4 rods that have a combination of Radio-frequency (RF) and direct current (DC) voltages applied to them. The combination is chosen to allow only ions with a specific m/z or a range of m/z to transmit through the analyzer. The voltages are all controlled by a computer. The quadrupole is a low resolution analyzer. They are often used as the first two parts of a tandem mass spectrometer with the first part acting as a mass selector, while the second is used as a collision cell allowing all the products to be transmitted to a third analyzer. When the third analyzer is a quadrupole, the instrument becomes ideal for quantitation by using selected reaction monitoring (SRM). SRM is similar to SIM mode, but uses two analyzers one set to select out a precursor for the molecule, while the second set for a fragment of the precursor ion.
Ion Trap mass spectrometer - Ion trap mass spectrometers is basically a three dimensional quadruple. This type of mass spectrometer can store and manipulate ions. It is more sensitive than a simple quadrupole for full scan mode. The ability to store and manipulate ions is used to not only to acquire tandem mass spectra, but multiple stage tandem mass spectra. Two limitations on the tandem mass spectrometer is that the lower m/z in the tandem mass spectra is 1/3 m/z of the precursor, and the fragmentation is not as extensive as instruments that use two quadrupole as the front end.
Time-of-Flight (TOF) mass spectrometer - TOF mass spectrometer are relatively simple mass spectrometers, because they basically just measure the time an ion takes to travel a specific distance with a specific kinetic energy. Larger m/z takes longer time to travel than the smaller m/z. These instruments are typically quite sensitive and fast. Improvements in technology have increased significantly the resolution of these instruments by use of reflectrons, increasing path length, and the use of pulsed voltages in the source. They do not have a natural m/z range, but are only limited by the detector and an ability to ionize the molecule. A variation of TOF is orthogonal acceleration TOF instruments, where a beam is pulsed into the instrument at a right angle. These orthogonal TOF instruments are commonly used for continuous ionization sources and as the third analyzer in hybrid instruments.
Fourier Transform mass spectrometry (Fourier Transform ion cyclotron resonance spectrometry)(FTMS) - While other mass analyzers have used Fourier Transformation in their analysis (for example, there was a FT-TOF instrument developed), FTMS usually refers to Fourier transform ion cyclotron resonance mass spectrometers. These instruments measure the frequency of the cyclotron motion caused by the ions in a magnetic field. The frequency of that motion is dependent on the m/z of the ions. These instruments can have extremely high resolution and mass accuracy, with the resolution dependent on time of observation (scan time) and the magnetic field. For a 7 Tesla magnet, a m/z ion would have 100,000 resolution at m/z 400 with a scan rate of 1 second per spectra (at m/z 800, it would be 50,000). A higher magnetic field increases the resolution. Two disadvantages of FTMS is the relatively slow scan speed and the maintenance of the superconducting magnets.
Orbitrap - Orbitraps are the newest mass analyzer, introduced in 2005 by Thermoelectronics. They are very similar in their advantages to FTMS, but do not require the superconducting magnets. Basically the analyzer measure the frequency of ions injected simultaneously into an electrostatic trap. The motion is harmonic in the electrostatic trap.