Resolving power double-focusing mass

These types of detectors have a limited resolving power in discriminating between small mass differences. In such cases, double focusing mass spectrometers are used. Fourier-transform ion cyclotron resonance (FTICR) analyzers interfaced with ESI or MALDI are used in the high molecular weight polymer characterization [44]. 

Figure 6.2. Nier-Johnson double-focusing mass spectrometer. The two sets of ion paths illustrate focusing for dispersion and for ion kinetic energy (shown in exaggerated form Ligon 1979). Modern commercial instruments give a resolving power of and mass measuring...

Resolving power decreases with increasing mass but spectrometers having a resolution of 1000, i.e. the ability to discriminate between m/z values of 1000 and 1001, or between 100 and 99.9, are adequate for many applications. Double-focusing instruments may be capable of resolutions of 20 000-50 000 or more. 

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