Electrostatic Analyzer Combination

The double-focusing combination of electrostatic- and magnetic-sector analyzers allows the inherent energy spread of the beam to be compensated for by design and ensures that there is no spread in the beam at the collector. 

Ion Optics of Magnetic/EIectric-Sector Mass Spectrometers 

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

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. 

The two magnetic stages are a 30-cm radius followed by an electrostatic analyzer with a radius of 43.26 cm. The vacuum system is metal and is bakeable to 300°C. The analyzer region of the instrument is pumped with ion pumps and is maintained at a pressure 10"9 torr. A combination titanium sublimation-ion pump is used to obtain operating pressures in the source region in the 10"8 torr range. A Nier thick-lens source (8), used in conjunction with a sample wheel arrangement (9), makes it possible to analyze as many as 10 samples per day. 

A few years ago, we began a research program to develop methods of analysis which would involve the use of FAB and a high performance tandem mass spectrometer. The tandem instrument was the first triple sector mass spectrometer to be designed and built by a commercial instrument company (Kratos of Manchester, U.K.). The first mass spectrometer of the combination is a double focussing Kratos MS-50 which is coupled to a low resolution electrostatic analyzer, which serves as the second mass spectrometer U). This FAB MS-MS combination has been used to verify the structures of an unknown cyclic peptide (2), a new amino acid modified by diphtheria toxin (3), and an ornithine-containing lipid (4). A number of methods have also been worked out which rely on this instrumentation. They Include the structural determination of cyclic peptides (5), nucleosides and nucleotides (6), and unsaturated fatty acids (7) and the analysis of mixtures of both anionic (8) and cationic surfactants (9). 

An electrostatic analyzer (ESA) can greatly reduce the energy distribution of an ion beam by forcing ions of the same charge (z) and kinetic energy (regardless of mass) to follow the same path. A slit at the exit of the ESA further focuses the ion beam before it enters the detector. The combination of an... 

Combinations of magnetic and electrostatic analyzers have been used to make instruments with high resolution capable (with appropriate calibration) of accurate mass measurements. Because they are scanning instruments, magnetic sector analyzers suffer from duty cycle limitations, as do quadrupole analyzers. Furthermore, because the scan speed of the magnetic field is proportional to resolution, additional time is required to obtain a spectrum as resolution is increased. Scanning the... 

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