Magnetic sector mass analyser

In a magnetic deflection mass spectrometer, ions leave the ion source and are accelerated to a high velocity. The ions subsequently pass through a magnetic sector in which the magnetic field is applied in a direction perpendicular to the direction of ion motion. By applying an acceleration perpendicular to the direction of motion of an object, the velocity of the object remains constant, but the object travels in a 

A schematic representation of a double-focussing mass spectrometer is shown in Fig. 10.4. For historical reasons, this set-up is referred to as a reverse-geometry magnetic sector mass spectrometer, which means that the magnetic sector precedes the electric sector [1]. 

Typically, the electric sector is held constant at a value which passes only ions having the specific kinetic energy. Therefore, the parameter that is most commonly varied is the magnetic field strength B, A magnetic field scan can be used to 

The resolving power of a magnetic sector mass spectrometer is determined by the slit widths. Higher resolution is obtained by decreasing the sUt widths, thereby decreasing the number of ions that reach the detector. 

Linked scans, in which the magnetic and electric fields are scanned together, can be used to perform MS/MS experiments (product, precursor, and neutral loss) with a double focussing mass spectrometer. 

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Walder AJ, Freedman PA (1992) Isotopic ratio measurement using a double focusing magnetic sector mass analyser with an inductively coupled plasma as an ion somce. J Anal At Spectrom 7 571-575... 

Figure 4.4. Illustrating the operation of a magnetic sector mass analyser.

Q. What are the advantages and disadvantages of magnetic sector mass analysers compared with quadrupoles ... 

Double focussing magnetic sector mass analysers provide a very high reproducibility, high resolution, and a high dynamic range. Their use is limited due to their size and higher cost compared to other mass analysers. 

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. 

Magnetic sectors can be used on their own, or in conjunction with energy analysers to fomi a tandem mass spectrometer. The unique features of the reverse geometry instrument are presented from this point. 

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