B–1
A P P E N D I X B
T h e o r y o f O p e r a t i o n
This appendix describes theories of operation for the Electrospray
Aerosol Generator.
S y s t e m D e s c r i p t i o n
The Electrospray consists of three main subsystems that are used
to generate a monodisperse aerosol.
Pressure chamber—capillary—Electrospray chamber
Air and CO
2
flow control
High-voltage control
The pressure chamber—capillary—Electrospray chamber schematic
is shown in Figure B-1. A description of how the Electrospray
generates aerosol follows.
A sample solution is stored in a cone-shaped vial, enclosed in a
cylindrical pressure chamber. The chamber accommodates a
capillary and a platinum high-voltage wire, both of which are
immersed in the solution. Maintaining a differential pressure
causes the solution to be pushed through the capillary.
The high-voltage control regulates an electrical field exerted at the
capillary exit, which pulls the charged solution out of the capillary,
forming droplets that are mixed with clean air and CO
2
. This
produces a sheath flow, which transports the droplets to the
Electrospray chamber. The highly charged droplets are neutralized
by a Polonium-210 source, and the liquid is evaporated before the
aerosol exits the instrument.
The remainder of this section discusses liquid flow in the capillary,
the Electrospray chamber design, aerosol neutralization, the flow
control system, and the high-voltage control and current
measurement methods used in the Electrospray.
