Download PM 8000 - Warner Instruments

4. PRINCIPLES AND TECHNIQUES FOR MICROINJECTION
USING THE BALANCE PRESSURE
There are two purposes when a balance pressure is applied to the injection pipette. The first purpose is to restrict
the inject pressure or suction vacuum to be buffered in the pipette after an action. . Another purpose is to compensate
the suction caused by a micropipette capillary action. The following two characteristics compare the injection output
with / without balance pressure:
INJECTING
PRESSURE
INJECTING
PRESSURE
PRESET
PRESSURE
PRESET
PRESSURE
BALANCE
PRESSURE
BALANCE
PRESSURE
TIME
INJECTION
PRESET TIME
TIME
INJECTION
PRESET TIME
Injection with balance pressure will
turn off at the correct timing.
PRESSURE
BUFFERED TIME
Injection without balance pressure will continue inject
for some time even the injection valve is turned off.
The smaller ID of a pipette, the stronger capillary action it has. There are different capillary action forces inside
a pulled micropipette because there are different IDs from the tip to unpulled portion of a pipette. Therefore,
to keep liquid inside a pipette closer to the tip, higher balance pressure must be applied. Other factors to effect
the applied balance pressure are the surface tension of the liquid and the depth of tip inserting in the liquid.
An example of balance pressure applied to a pulled pipette as following :
Balance Pressure:
0.06 psi
0.06 psi 0.35 psi
1 psi
1.5 psi
3 psi
4.5 psi
0.58 mm I.D.
1 mm O.D. pipette
10 um tip opening
The liquid boundary
The pulled pipette can be precisely controlled to suck or inject by the microinjector. The following
characteristic chart shows the princeple of suction or ejection corresponding to different valve action for the
pipette above:
<
Suction from the pipette tip
> < Ejection from the pipette tip >
Turn on INJECT valve
Turn on FILL
valve
Turn on BALANCE and VENT valves
Turn on BALANCE valve only
Turn on VENT valve only
Output port
pressure : -20" Hg
0 0.2 psi 4.5 psi
Adjustable range of
ejection or suction :
Capillary action balance point at
10um tip opening
10 psi
^
20 psi
SUCTION AND EJECTION CHARACTERISTIC OF A PIPETTE TIP
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