Introducing the MSQ
_______________________________________________ The Source–An Introduction to API Techniques
Electrospray Ionization Using the MSQ Source
The sample, in solution, enters the source via a stainless steel insert capillary
held at a voltage of 3 to 5 kV. The insert capillary is surrounded by a tube
that directs a concentric flow of nitrogen nebulizing gas past the droplets of
liquid forming at the probe tip. The action of the nebulizing gas, high
voltage, and heated probe produces an aerosol of liquid droplets containing
ions of the sample and solvent. The ion evaporation process is assisted by a
second concentric flow of heated nitrogen gas. This is the sheath gas. This
highly efficient evaporation process close to the entrance cone enables the
routine use of high LC flow rates (up to 2.0 mL/min) in ESI mode.
The newly formed ions then enter the focusing region through the entrance
cone. This is due to the following:
The high electric field. The insert capillary is at 3 to 5 kV with respect
to the rest of the source, which is typically at 20 to 30 V.
•
•
The gas flow into the focusing region.
Ions then exit the focusing region and pass into the RF lens. The RF lens
(square quadrupole) helps to focus the ions before they enter the mass
analyzer region.
Atmospheric
Pressure
Region
Insert capillary
Region
LC eluent
Nebulizing gas, N
2
Sheath gas, N
2
Probe
Insert
Intermediate
Pressure
Region
Rotary
pump
Entrance cone
Exit cone
Cone Wash
Figure 1-10. Schematic of the ESI source on the MSQ, showing the
principal components and pressure regions
___________________________MSQ Hardware Manual ___________________________
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