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Electrospray-Ion Trap Mass Spectrometry

Electrospray analyzes a liquid spray, such as that emitted from High Pressure Liquid Chromatography or from direct spray of a liquid sample. The solvent evaporates, leaving non-volatile ions in the gas phase. These ions are often multiply charged so a pattern of ions is obtained for each mass (e. g. M+5H, M+6H, M+7H, etc.). As a result, Mass/Charge is analyzed in the range of 1-3000, even for proteins of 100,000 molecular weight or more. Computer software is used to identify the patterns and present a deconvoluted mass/charge ratio for each molecular species.

The analyzer used in the LCQ instrument is an ion trap. This analyzer is noted for high sensitivity and the ability to perform MSn. The trapped ions can be repeatedly fragmented to obtain structural information such as peptide or nucleic acid sequence or other structural solutions. High sensitivity allows analysis of as little as 5 femtomoles of a peptide. Fragmentation patterns have been used to identify other structural features such as protein phosphorylation, etc. Naturally, these mass spectrometers are useful for many biomolecules other than proteins and nucleic acids.

Software is available to search databanks for short peptide sequences, patterns of peptides from protease digestions, etc. and identify unknown proteins