Mass analysis magnetic sector

The ICP/MS is an elemental and isotopic analysis method that was first developed in the early 1980s. The ICP had been used only as a source for emission spectroscopy until it was adapted for producing ions for a mass analyzer (Douglas and French, 1981 Houk et al., 1980 Houk et al., 1981 Houk and Thompson, 1982). Since 1983, several manufacturers have sold ICP/MS instruments that incorporate various mass analyzer systems, such as quadrupole mass filter, magnetic sector field, time-of-flight, Paul ion trap, and ion detection systems such as the electron... 

Ion formation and fragmentation in the source is followed by mass analysis. Mass analyzers are used to separate ions based on their mass-to-charge ratios. Organic chemists commonly use two types of mass analyzers magnetic sector instruments (low- and high-resolution) and quadrupole instruments. Magnetic sectors separate ions based on dispersion of the ions into beams with different miz ratios quadrupoles are mass filtering devices. 

Another approach to mass analysis is based on stable ion trajectories in quadnipole fields. The two most prominent members of this family of mass spectrometers are the quadnipole mass filter and the quadnipole ion trap. Quadnipole mass filters are one of the most connnon mass spectrometers, being extensively used as detectors in analytical instnunents, especially gas clnomatographs. The quadnipole ion trap (which also goes by the name quadnipole ion store, QUISTOR , Paul trap, or just ion trap) is fairly new to the physical chemistry laboratory. Its early development was due to its use as an inexpensive alternative to tandem magnetic sector and quadnipole filter instnunents for analytical analysis. It has, however, staned to be used more in die chemical physics and physical chemistry domains, and so it will be described in some detail in this section. 

The beam entering the ion chamber is suitable for both electron (El) and chemical (Cl) ionization, and either mode can be used (Figure 12.3). Mass analysis follows in the usual way, typically using quadruple or magnetic-sector instruments. 

The choice of mass spectrometer for a particular analysis depends on the namre of the sample and the desired results. For low detection limits, high mass resolution, or stigmatic imaging, a magnetic sector-based instrument should be used. The analysis of dielectric materials (in many cases) or a need for ultrahigh depth resolution requires the use of a quadrupole instrument. 

In both electron post-ionization techniques mass analysis is performed by means of a quadrupole mass analyzer (Sect. 3.1.2.2), and pulse counting by means of a dynode multiplier. In contrast with a magnetic sector field, a quadrupole enables swift switching between mass settings, thus enabling continuous data acquisition for many elements even at high sputter rates within thin layers. 

Magnetic sector mass spectrometers accelerate ions to more than 100 times the kinetic energy of ions analysed in quadrupole and ion trap mass spectrometers. The higher accelerating voltage contributes to the fact that ion source contamination is less likely to result in degraded sensitivity. This is particularly important for analysis that requires stable quantitative accuracy. 

Applications Sector instruments are applied for niche applications such as high-resolution measurements and fundamental ion chemistry studies. Magnetic sector mass spectrometers remain the instrument of choice in areas of target compound trace analysis, accurate mass measurement and isotope ratio measurement. 

Magnetic sectors have medium transmission (10-50 percent), large mass range (m/z > 10000, where m is the mass of the ion and z the charge) and excellent mass resolution (m/Am > 104). This high mass resolution makes these analysers appropriate for SIMS analysis in semiconductor research. 

Different mass analysers can be combined with the electrospray ionization source to effect analysis. These include magnetic sector analysers, quadrupole filter (Q), quadrupole ion trap (QIT), time of flight (TOF), and more recently the Fourrier transform ion cyclotron resonance (FTICR) mass analysers. Tandem mass spectrometry can also be effected by combining one or more mass analysers in tandem, as in a triple quadrupole or a QTOF. The first analyzer is usually used as a mass filter to select parent ions that can be fragmented and analyzed by subsequent analysers. 

In some cases, more than one mass spectrometer may be used to carry out the analysis of a sample. Thus, the components from the first MS analysis may be passed to another MS for further analysis. In this type of analysis, a fragment from the first MS analysis is further broken down and the resulting new fragments are analyzed. This allows for analysis of complex samples. Because there are several types of sample ionization (e.g., El, Cl, and electrospray) and different types of mass spectrometers (e.g., quadrupole, time of flight [TOF], and magnetic sector) there are several different ways an MS-MS analysis can be carried out. 

This basically means that two instruments have been linked together. The first analyser can replace the traditional chromatographic separation step and is used to produce ions of chosen m/z values. Each of the selected ions is then fragmented by collision with a gas, and mass analysis of these product ions effected in the second analyser. The resulting mass spectrum is used for their identification. The potential combinations of the various magnetic sector and quadrupole instruments to form such coupled systems is considerable. Ion traps may also be operated in a tandem MS mode. 

---