Double-focusing spectrometer

Double-focusing spectrometer an electromagnetic instrument that focuses the ions with a given m/z ratio even though their initial directions diverge and their kinetic energies are different. 

Why are detection limits in ICP-MS generally lower with double-focusing. spectrometers than with quadrupole mass spectrometers ... 

Figure 16.5 Mass spectrometer with magnetic analyser, (a) Nier-Johnson assembly (b) View of the directional focusing by the magnetic sector (the entrance and exit planes are oblique with respect to the angle of incidence of the beam, ensuring focusing) (c) Mattauch-Herzog assembly (d) Arrangement of a double focusing spectrometer (e.g. R = 40 cm and R = 60 cm).

Ion microprobe analyzers are more sophisticated (and more expensive) instruments based on a beam of primary ions focused to a diameter of 2(X) nm to 1 pm. This beam can be moved across a surface (rastered) for about, 3(K) pm in both the. v and y directions, A. microscope is provided lo permit visual adjustment of the beam position. Mass analysis is performed with a double-focusing spectrometer. In some instruments, the primary ion beam passes through an additional low-resolution mass spectrometer so that only a single type of priniilry ion bombards the sample. The ion mi-croprobc veisioii of SIMS permits detailed studies of solid surfaces. 

Magnetic sector analysers are considered to be medium-resolution instruments with f <2000. They are also an important component in the high-resolution double-focusing spectrometers discussed next. 

FIGURE 7.7 The two most popular mass analyzers. The magnetic sector instrument is normally configured in tandem with an electrostatic analyzer that narrows the kinetic energy spread of the ion beam. For this reason, it is called a double-focusing spectrometer. 

The GD-MS technique has been employed most commonly for the quantitative analysis of traces and ultratraces in high-purity materials. GDs have been successfully coupled to different types of mass analyser, mainly of sequential nature such as quadrupole and double-focusing spectrometers. However, for analysis with high depth resolution it is required to use mass analysers able to carry out rapid collection of complete mass spectra with high precision and sensitivity, such as TOFMS. It has been demonstrated that, as in GD-OES, depth profile analysis of conducting, semiconducting or insulating materials is possible by GD-TOFMS, with depth resolutions in the order of nanometres. Additionally, GD-TOFMS provides molecular information from samples such... 

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