Interpreting Electrospray Mass Spectra
"an IonSource.Com tutorial"
page 3

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Electrospray Ion Generation

 

 

 

 

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Electrospray Example
Droplets are generated when a high voltage is applied to a  liquid stream, this technique is known as electrospray.  For example the liquid stream could be the effluent from an HPLC.  This method for droplet generation has been used in various applications since the early part of the 1900s.  In electrospray larger droplets explode into smaller droplets and so on until the analyte enters the gas phase as an ion. Pure electrospray in the context of mass spectrometry is accomplished without a nebulizing gas.  At higher LC flow rates a sheath gas is used to aid in the nebulization process.  Some call this method "pneumatically assisted electrospray."  

 

In this example a single peptide is ionized to produce a population of charged and uncharged peptides.  The number of positive charges that a molecule can support is generally related to the number of basic sites on the molecule.  In positive ion mode the analyte is sprayed at low pH to encourage positive ion formation.  In negative ion the analysis is normally carried out well above a molecules isoelectric point to deprotonate the molecule.  The basic principle of all mass spectrometers is that a molecule must be charged (ionized) before the mass spectrometer can influence it in an electric field.  The next page shows how this population of molecules might appear on a mass spectrum. 

Note:  Most peptides obtained from a trypsin digest have two potential sites for protonation, the amino terminus and the basic C-terminal residue, lysine or arginine.

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Last updated: Monday, July 18, 2005 01:43:20 PM