Quattro 2 User's Guide, issue 2. 6666533 - Waters

Quattro II
User's Guide
Ionisation Techniques
Electrospray
Electrospray mass spectrometry (ESMS) allows very large and very labile molecules
to be analysed routinely. The sample, in solution, emerges from a high voltage
capillary tube into a strong electrostatic field at atmospheric pressure producing an
aerosol of highly charged droplets. Evaporation of solvent from these droplets results
in sample ions. In the case of proteins and other biomolecules, such ions may carry
several electronic charges.
Electrospray is compatible with on-line HPLC and capillary electrophoresis but is
restricted to polar samples.
Atmospheric Pressure Chemical Ionisation
Atmospheric pressure chemical ionisation (APcI) is a soft ionisation technique able to
accept the entire eluent from a standard 4.6mm diameter HPLC column.
Sample droplets are vaporised in a heated chamber before emerging into a region of
solvent ions formed within the atmospheric pressure source by a corona discharge.
Ionisation occurs as a result of chemical reactions between the sample molecules and
solvent ions.
The Combined EI/CI Source
Most Quattro II systems are equipped with a combined source capable of operating in
both the electron impact (EI) and chemical ionisation (CI) modes. In either mode, the
source may be used in conjunction with the reference inlet, the insertion probe, the
GC inlets or the particle beam interface.
Electron Impact
Electron impact is the classical ionisation technique in which gas phase sample
molecules are ionised in collisions with high energy electrons. The source is heated to
ensure sample vaporisation.
Chemical Ionisation
When the combined EI/CI source is operated in the chemical ionisation mode, a
reagent gas is admitted to the source at a relatively high pressure. The gas molecules
are ionised by the electron beam. Sample ions are generated in reactions with these
gas ions. CI is a “softer” ionisation technique than EI, producing less sample
fragmentation and generally a stronger molecular ion.
Desorption Chemical Ionisation
Polar samples, liable to decomposition under normal CI conditions, are deposited on
the tip of the DCI probe and thermally desorbed into a CI environment.
Instrument Description
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