Single Focusing Instruments

In the presence of a magnetic field perpendicular to the direction of the motion of the ion beam, each ion experiences a force at right angles to both its direction of motion and the direction of the magnetic field, thereby deflecting the ions to a circuit. The radius of the circuit is proportional to (m/z) (Eq. (1)) so that the magnetic field is sufficient for mass analysis of an ion beam  

Mono-energetic ions with various masses and/or different charges pass the magnetic sector with different circular paths. The radius of a circular path from an ion with large mass number is greater than that of an ion with lower mass number (Fig. 2). 

In a particular arrangement of the magnetic and electric sectors (Mattauch-Herzog geometry) simultaneous double focusing for all masses can be achieved in the same plane , permitting the use of a photographic plate (Fig. 3). 

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In single focusing instruments the beam of accelerated ions enters a magnetic field of constant intensity H, and experiences a force perpendicular to the field. Undef the influence of this force the ions assume a radial path in accordance with the relation... 

Besides nonvolatility, the resolving power of the available single-focusing instruments limits the applications of MS to compounds of a molecular weight up to a maximum of about 1,200. Technical improvements and the new double-focusing instruments will probably raise this limit in the near future. 

Mass spectrometers with only a sector magnetic field for mass analysis are known as single-focusing instruments. A well designed single-focusing spectrometer may have resolution as high as 5000. In mass spectrometry, resolution R is defined as... 

Why do double-focusing mass spectrometers give narrower peaks and higher resolutions than single-focusing instruments. ... 

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