Eppendorf FemtoJet express - Manual (Page 22)

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3.4.1 Compensation pressure p
c
The compensation pressure pc ensures that no medium flows into the capillary. Capillary forces
would make liquid flow out of the cell culture dish into the injection capillary and thus dilute the
injection material. To prevent this, a permanent compensation pressure pc is set. This should be
selected so that there is a permanent slight flow-out of liquid from the injection capillary. The
individual pressure level can be determined in a preliminary test. For example, a fluorescent dye
can be added to the capillary to enable outflow to be monitored directly. The pressure required
is heavily dependent on the surface tension and viscosity of the injection material. Experience
has shown that compensation pressures of between 30 hPa and 300 hPa (0.44 – 4.4 psi) are
appropriate values for ready-to-use Eppendorf Femtotips
® injection capillaries.
Pressure in the capillaries
3.4.2 Injection pressure p
i
Injection pressure p
i
is applied during the injection process. This pressure is generally higher
than the compensation pressure. In many cases, a pressure between 50 hPa and 500 hPa
(0.73 – 7.2 psi) is appropriate for Femtotips
®
. The volume injected is dependent on the injection
pressure and the injection time. The injection pressure must be greater than the internal
pressure of the cell into which injection should take place. However, if the cell or the cell nucleus
swell up during injection, the injection pressure is too high.
3.4.3 Injection time t
i
Injection time t
i
gives the period for which injection pressure pi is maintained. t
i
is usually
selected from a range between approx. 0.3 s and 1.5 s. The relevant factor for the injected
volume is the product of the injection pressure and the injection time.
Depending on the setting on the Eppendorf Micromanipulator which is connected, the injection
time t
i
is measured from the point at which the key is pressed. The injection pressure is
built up immediately, so it is already present
during the injection movement and during penetration of the cell. Once the end of injection time
has been reached, the device switches to compensation pressure p
c
. At the same time, the
micromanipulator is moved back into the working level. When "Injection at Z limit" is set,
measurement of the injection time t
i
does not begin until the Z limit has been reached. Once t
i
has elapsed, the FemtoJet ® switches back to p
c
and the micromanipulator moves back into its
starting position in the working level
Capillary suction
Compensation pressure p
c
Hydrostatic pressure P
hyd
Mode of operation
3 Mode of operation
3
03_Bedienung_en.fm Seite 70 Freitag, 29. Juni 2007 2:49 14