Tandem mass spectrometry in electromagnetic analysers

Instruments with combined magnetic and electric analysers can be assembled according to either of two configurations. The electric sector is located either in front of the magnetic sector, which is the most frequent case, or behind it. The magnetic sector is labelled B and the electric sector is labelledE. The first configuration is called EB (or also Nier-Johnson ). 

The geometry is less frequently a BE one. It is sometimes called a reverse Nier-Johnson or reverse geometry . This geometry allows an easier analysis of the ion kinetic energy (IKE or MIKE spectrometry). 

MS/MS is possible with a double sector instrument even though it cannot exactly be considered as made up of two mass spectrometers hooked in series. A technique called linked scan is used. It consists of a simultaneous scan of the E and B sectors according to a mathematical relationship depending on the system geometry, on the region under study and on the type of information that is looked for. These different types of scans are listed in Table 2.4. 

We will now examine the most common types of scans. 

All of the ions have the same kinetic energy at the source outlet. If an ion dissociates in a field-free region, the fragments have approximately the same velocity as the precursor ion and thus have different kinetic energies from that of the precursor ion. Since the electric sector sorts the ions according to their kinetic energy, all of the metastable ions formed 

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