Mass Spectrometers and Mass Spectral Analysis
Essentially, a mass spectrometer measures mass-to-charge (m/z) ratios of analytes such as nucleic acids, oligonucleotides, proteins, peptides or peptide fragments. It has three components, ionization source, the m/z analyzer and the detector.

Simplified schematic of a Mass Spectrometer

In 1890, J.J Thomson introduced the first mass spectrometer, which employed fixed magnetic and electric fields (described as electric sector and magnetic sector) to separate ions of different mass and energy. He recognized that charged particles that differ in momentum behave differently in an electromagnetic field and used this property for separation of ions with different masses. Using this instrument, he was able to prove that the noble gas Ne (Neon) was composed of two different isotopes of mass 20 Da and 22 Da. These so called ‘sector instruments’ are not very sensitive in comparison with recent mass spectrometers and are now more or less of historical importance. Some advantages although not unique, are their relatively high mass range, sensitiveity and resolving power, and their compatibility with wide range of ionization techniques. The disadvantages are their size and cost compared to most other mass spectrometers developed later.