Mass filtering discrimination

The mass analyser (sometimes called mass filter) is the discriminating element in a mass spectrometer and is where the ions are manipulated and sorted. There are a number of types of mass analyser in MS and among them are ... 

Low-pressure ion detectors for IMS are typical of those used in mass spectrometry. In fact, whenever low-pressure ion detection methods are used with IMS, the IMS is interfaced to a mass spectrometer. Mass spectrometers after IMSs serve as mass filters or mass dispersive devices prior to low-pressure ion detection. Mass discrimination is not necessary, however, as in the case of a quadrupole mass spectrometer operating in the radio frequency (RF)-only regime, where complete ion mobility spectra can be obtained. A more detailed discussion of the advantages... 

In Eq. (8.50) Ip, I, are the signal amplitudes of product ions and reagent ions (H3O+, H30. H20, etc.) corrected for differential diffusion in the flow tube and mass discrimination in the downstream quadmpole mass filter. Additional parameters fj., f 2 may also be included in the reactions of 1130 reagent ions to account for analytes where not all water cluster ion reactions with the analyte are reactive [98]. 

Reaction mechanisms using highly reactive gases and discrimination by selective bandpass mass filtering... 

Let us now go on to discnss the other major way of interference rejection in acollision/ reaction cell using highly reactive gases and mass (bandpass) filtering discrimination. 

Reaction Mechanisms with Highly Reactive Gases and Discrimination by Selective Bandpass Mass Filtering... 

Another way of rejecting polyatomic interfering ions and the products of secondary collisions/reactions is to discriminate them by mass. As mentioned previously, higher-order multipoles cannot be used for efficient mass discrimination because the stability boundaries are diffuse and sequential secondary reactions cannot be easily intercepted. The only way this can be done is to utilize a quadrupole (instead of a hexapole or octapole) inside the collision/reaction cell and use it as a selective bandpass (mass) filter. There are a number of commercial designs using this approach, so let us take a look at them in greater detail in order to better understand how they work and how they differ. 

Because of the disparity of the reaction rates of the two neutralization reactions, the analyte can be efficiently determined after the introduction of ammonia as a reactive gas into the multipole. There are many excellent reviews about the development and applications of collision/reaction cell in ICP-MS. " In order to eliminate the new isobaric interferences produced by secondary reactions, two methods are commonly used in the commercial instrument the discrimination of kinetic energy or mass filtering. " The former mainly utilizes the post-cell kinetic energy discrimination (KED) to suppress transport of the produces of the side reactions to the analyte in the hexapole and octapole cell instruments. Whereas in the latter, the quadrupole cell has a capability to reduce the formation of the unwanted side product ions by selecting an appropriate mass bandpass. The details of the KED and bandpass approaches can refer to many excellent books and reviews. " " ... 

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