Mass spectrometry is a technique for separating and identifying molecules based on mass. It has become an important tool for proteomics, the analysis of the whole range of proteins expressed in a cell. Mass spectrometry is used to identify proteins and to determine their amino acid sequence. It can also be used to determine if a protein has been modified by the addition of phosphate groups or sugars, for example. The technique also allows other molecules, including DNA, RNA, and sugars, to be identified or sequenced.

The use of mass spectrometry has greatly aided proteomics. Whereas DNA sequencing is simple and straightforward, protein sequencing is not. The ability to quickly and accurately identify proteins being expressed in a cell allows a range of hypotheses to be tested that cannot be approached by simply looking at DNA. For instance, it is possible with mass spectrometry to determine...