Magnetic Analyzers

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

Electrostatic analyzer. A velocity-focusing device for producing an electrostatic field perpendicular to the direction of ion travel (usually used in combination with a magnetic analyzer for mass analysis). The effect is to bring to a common focus all ions of a given kinetic energy. 

Mass spectrometer configuration. Multianalyzer instruments should be named for the analyzers in the sequence in which they are traversed by the ion beam, where B is a magnetic analyzer, E is an electrostatic analyzer, Q is a quadrupole analyzer, TOP is a time-of-flight analyzer, and ICR is an ion cyclotron resonance analyzer. For example BE mass spectrometer (reversed-geometry double-focusing instrument), BQ mass spectrometer (hybrid sector and quadrupole instrument), EBQ (double-focusing instrument followed by a quadrupole). 

Neir-Johnson geometry. An arrangement for a double-focusing mass spectrometer in which a deflection of nil radians in a radial electrostatic-field analyzer is followed by a magnetic deflection of 7t/3 radians. The electrostatic analyzer uses a symmetrical object-image arrangement, while the magnetic analyzer is used asymmetrically. 

All analyzers use one or more of three basic principles (a) magnetic analysis, (b) electrostatic analysis, and (c) time-of-flight analysis. Magnetic analyzers of single and double focusing types are by far the most common ones currently in use, and will serve to illustrate the methods of analysis. Two other types of analyzers which have gained popularity for analytical applications but are omitted in the fol-... 

Figure 2.1 Mass spectrometric approach. Dl, direct inlet GC, gas chromatography HPLC, high performance liquid chromatography CZE, capillary zone electrophoresis El, electron ionization Cl, chemical ionization ESI, electrospray ionization DESI, desorption electrospray ionization APCI, atmospheric pressure chemical ionization MALDI, matrix assisted laser desorption ionization B, magnetic analyzer E, electrostatic analyzer...

Figure 2. Schematic drawing of the AEl IM-20 ion microprobe. The magnetic analyzer and ion counting system are linked to an on-line computer for automated...

How can metastable ions be registered with a classic magnetic sector mass spectrometer (See Chapter 2, Section 2.2.2) Let ion mj+ leave the ion source and after acceleration with accelerating voltage V fragment, with formation of ion m2+ and a neutral particle m3° between the source and magnetic analyzer (first field-free region, 1 FFR). 

As m1 = m2 + m3, both equations may be true only in the case that V = v2 = v3, that is, in the first approximation both products of fragmentation move in the same direction and with the same speed as their parent ion. Any magnetic analyzer is an analyzer of momentum. Thus, a metastable ion with real mass m2 and velocity V will be registered together with stable ion m with velocity v (Equation 5.4) if their momentums are equal. 

For this experiment Bainbridge used the high-precision mass spectrograph he had developed by combining a Wien filter with a 180° magnetic analyzer.13... 

The high-resolution ICP-MS instruments are all based on a reverse Nier-Johnson geometry with an electrostatic and a magnetic analyzer [14,20]. The routinely observable resolution is between 3000 and 10 000 m/Am. This resolution is sufficient for the resolution of a number of molecular ion interferences such as ArO+ on 5<%e and ArCl+ on 75 As as prominent examples. Other molecular ion interferences are still not resolvable. 

From these spectra, the (skimmer + ion-source + magnetic analyzer + lens transport) efficiency was roughly estimated to be better than 1-0 %. 

The Nu Instruments Nu Plasma displays some general similarities to the P54, but critical features are radically different in concept. Most importantly, the instrument deploys novel variable dispersion ion optics that are applied to the ion beams exiting the magnetic analyzer, permitting the use of fixed multiple collectors and rapid peak switching. 

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