Eppendorf FemtoJet - Manual (Page 23)

21
3 Mode of operation
3.4.1 Compensation pressure p
c
The compensation pressure p
c
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 p
c
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.
If the compressor starts up occasionally during experiments, this does not
impair the function of the FemtoJet

. Pressure is always available up to
the maximum value of 6,000 hPa (approx. 87.0 psi), even when the
compressor is topping up the supply pressure.
Capillary suction
Compensation pressure p
c
Hydrostatic pressure P
hyd
03_Bedien_en.fm Seite 21 Mittwoch, 27. September 2006 5:12 17