Mass analyzers characteristics

Heating inorganic substances to a high temperature on a metal filament yields characteristic positive ions that can be mass analyzed for m/z value and abundance to obtain accurate isotope ratios. 

The basic instrumental set-up for dynamic SIMS is the same as for SSIMS (Sect. 3.1.2). Depending on the intensity, beam diameter, and ion species needed, dif ferent ion sources are used. Several mass analyzers with different characteristics enable a broad field of applications. 

Figure 3.10 HPLC/MS/MS tandem mass spectrum of 3-Glc-28-Glc medicagenic acid obtained using an ion-trap mass analyzer. The spectrum illustrates the successive loss of two hexoses, the deprotonated aglycone, and a characteristic ftagment ion associated with medicagenic acid saponins.

The first mass analyzer was used to select a given m/z value and those ions would be transmitted to the collision region where they would undergo collisional activation. Subsequent decomposition of the excited ions resulted in characteristic fragment ions (with equally characteristic... 

What characteristic of ESI permits large biomolecules (Mr> 10,000) to be analyzed using mass spectrometers having modest mass range capabilities (multiple charging reduces the effective mass to within the accessible mass range of conventional mass analyzers). 

One important characteristic of the mass analyzers used in GC is that they do not offer high resolution 0.1-1 Da resolution in the mass range of 10-800 is sufficient. 

Under the headline of instmmentation we shall mainly discuss the different types of mass analyzers in order to understand their basic principles of operation, their specific properties and their performance characteristics. Of course, this is only one aspect of instmmentation hence topics such as ion detection and vacuum generation will be addressed in brief. As a matter of fact, sample introduction is more closely related to particular ionization methods than to the type of mass analyzer employed, and therefore, this issue is treated in the corresponding chapters on ionization methods. The order of appearance of the mass analyzers in this chapter neither reflects the ever-changing percentage they are employed in mass spectrometry nor does it strictly follow a time line of their invention. Instead, it is attempted to follow a trail of easiest understanding. 

In a TOP mass analyzer, ions of different mIz ratios are determined by the time they take to travel through a field-free path of known length between the source and the detector. The ions are accelerated by application of an electrical potential. The velocity of an ion is inversely proportional to its mass therefore, each m/z has a characteristic TOP (de Hoffman and Stroobant, 2001). 

Different mass analyzers may impose unique technical requirements when interfaced to LC. Understanding the operating principles and technical properties of both LC/MS interfaces and mass analyzers is deemed beneficial. A brief overview of the history of the development of LC/MS interfaces is given in Section II, which is followed in Section III by a summary of working principles and characteristics of commonly used mass analyzers. 

Argon is analyzed by mass spectrometry (characteristic ion m/z 40) or by gas-solid chromatography. Its concentration can be increased by several times by selective adsorption over a suitable adsorbent followed by thermal desorption of the gas onto the GC injection port. 

The general characteristics of a mass analyzer are accuracy, resolving power, mass range, and tandem analysis capabilities. 

Full Scan The mass analysis process by which a controlled series of m/z are allowed to be detected. The m/z range over which a mass analyzer can be used (e.g., m/z 20 to 4000) is one defining characteristic of the instrument. 

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