Transmission and Dynamic Range

Other important quantities to consider when judging the suitability of a particular type of mass spectrometer are its transmission and its dynamic range. The term transmission reflects the fact that not all ions entering a mass spectrometer will make it all the way to the detector. Losses can be caused by a variety of factors, such as unstable ion trajectories, collisions of ions with the solid parts of grid electrodes, imperfect performance of ion lenses and the scattering of ions by residual background gas molecules. The transmission for some types of mass spectrometer can exceed 90% while in others it may be rather low ( 10%). However, when transmission is referred to in mass spectrometry it is normally in 

Clearly the transmission is an important quantity to take into account for any quantitative analysis. In particular it is important to know how the transmission varies with miz for a given instrument. The transmission curve for a PTR-MS instrument can be determined in two ways. One option is to add selected compounds with different masses and known concentrations which are then detected following proton transfer. The relative ion signals from each compound can then be equated with the relative ion transmission values at the respective mJz values. However, this approach assumes no fragmentation and equal proton transfer rate coefficients. The latter issue can be avoided by separately calibrating the instrument for each of the compounds using one of the procedures discussed in Chapter 4. 

Analyser type Mass resolving power Mass range Linear dynamic range 

TOF-MSs. The operating principles behind each of these types of mass analyser will now be discussed in the next few sections. 

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