Analyzer combinations

Tandem mass spectrometers most commonly used for MS/MS smdies include the following analyzer combinations, although many others are possible ... 

Double-focusing analyzer. A magnetic analyzer and an electrostatic analyzer combined in either sequence to effect direction and velocity focusing. 

Tandem MS has been more or less successfully performed with a wide variety of analyzer combinations. What analyzers to combine for a certain application is determined by many different factors, such as sensitivity, selectivity, and speed, but also size, cost, and availability. The two major categories of tandem MS methods are tandem-in-space and tandem-in-time, but there are also hybrids where tandem-in-time analyzers are coupled in space or with tandem-in-space analyzers. Moreover, the ongoing development of faster electronics and high-voltage circuits as well as better software tools and hardware control devices constandy open up new possibilities of making innovative combinations of analyzers for specific applications. In this chapter a few examples of commercially available tandem MS instruments are presented. A brief summary of their weaknesses, strengths, and main areas of applications is given. 

One of the strengths of the isobole method is that it can be used to analyze combined effects of compounds irrespective of the shape of their dose-response curves. It is possible to assess mixtures of agents with dissimilar dose-response relationships, even when the maximal effects are not identical (Kortenkamp and Altenburger 1998). 

There are several types of ionization sources [MALDI, ESI, FAB (fast atom bombardment), PD (Cf-252 plasma desorption), El (electron ionization), Cl (chemical ionization) etc.], different types of mass analyzers [combinations of magnetic and electric sectors, quadrupolar filters (Q) and ion traps (IT), time-of-flight (TOF) and FT-ICR] and different detectors, each with its own advantages and drawbacks. We describe herein only the systems that presently have widespread use for the study of biomolecules ESI coupled to a quadrupole (or triple quadrupole, QqQ) mass analyzer or an ion trap, the MALDI source with the linear or reflectron TOF analyzer, and the FT-ICR system which can be equipped with both ESI and MALDI sources. 

Double-focusing analyzer. A magnetic analyzer and an electrostatic analyzer combined in either ------sequence to effect direction and velocity focusing.------------------------------... 

Figure 7 (a) Inhalation measurement cell with Malvern Spraytec laser diffraction analyzer, combined with Andersen cascade impactor (76). (b) Time-history showing the mean particle size measured during the actuation of the Clickhaler containing the micronized (M-SX) and supercritically produced (S-SX) salme-terol powders in formulation with lactose and at the airflow rate 49 L/min. 

While the development of ESI and MALDI provided techniques that ionize polar compounds effectively the spectra provide little or no structural information because molecular species are the only ions formed. The need to investigate not only the mass but also the structure of ions was an important factor in the development of multianalyzer mass spectrometers. There are several formats of MS/MS systems based on combinations of quadrupole, ion trap (Q and FT), and TOF analyzers. Combinations that use the same type of analyzers are tandem instruments, whereas different separation methods are used in sequence in hybrid systems. In MS/MS instruments, the first analyzer is used (usually) to select an ion of interest that is then passed, with or without fragmentation, into a second analyzer, which is often of higher resolving power and can be used for accurate mass measurement. 

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