Mass-spektrometriya

FTMS attribute	Effect of Magnetic Field Strength B
What it means:
Resolution (m/Δm)	Directly proportional to B	Improves mass accuracy and the ability to get isotopic resolution on large macromolecules.
Kinetic energy	Directly proportional to B^2	Increases the fragmentation and also ability to fragment larger macromolecules.
Ion capacity	Directly proportional to B^2	Can store more ions before space-charge adversely affects performance.

Figure 2.17: Fourier transform ion cyclotron frequency increases with magnetic field strength. The increased frequency improves accuracy as it allows for more measurements to average.
Because ion frequency = K*B*z/m, larger magnetic fields provide a higher frequency for the same m/z, therefore more data points are generated to define the frequency more precisely which ultimately increases accuracy (Figure 2.17).
Quadrupole-FTMS and quadrupole linear ion trap-FTMS mass analyzers that have recently been introduced are typically coupled to electrospray ionization sources. The quad-FTMS combines the stability of a quadrupole analyzer with the high accuracy of a FTMS. The quadrupole can act as any simple quadrupole analyzer to scan across a specified m/z range. However, it can also be used to selectively isolate a precursor ion and direct that ion into the collision cell or the FTMS. The resultant precursor and fragment ions can then be analyzed by the FTMS.
Performing MS/MS experiments outside the magnet presents some advantages since high resolution in FTMS is dependent on the presence of high vacuum. MS/MS experiments involve collisions at a transiently high pressure (10^-6 - 10^-7 Torr) that then has to be reduced to achieve high resolution (10^-10 - 10^-9 Torr). Performing MS/MS experiments outside the cell is thus faster since the ICR cell can be maintained at ultra-high vacuum. This makes the newer hybrid instrument designs are optimum over coupling FTMS/MS to separation techniques such as LC.
View Table 2.2

Table 2.2: A general comparison of mass analyzers typically used for electrospray. These values vary with instrument manufacturer.