Genevac HT-8 & HT-12 Series II Evaporating Systems
04-4541
Issue 1-9 – June 2008
Page 41 of
64
Limiting the chamber pressure
•
Bumping must be avoided, as it is a potential
source of cross contamination between samples.
•
Bumping can also cause product to be deposited
on the glass lenses as previously described
Linking Runs
Use the Dri-Pure option on the drop down menu
under
Pressure Control Regime
on the
Run Edit
screen.
This option incrementally reduces the pressure and
automatically sets the rotor speed to high.
6.3
Optimising a run
This section will describe some of the general
principles applicable to optimising evaporation rates
by exploiting the flexibility of the Series II control
software.
Pressure control can be used to significantly
increase the evaporation rate of mixtures of greater
than 30% water when contained in glass tubes and
beakers.
When evaporating aqueous mixtures at pressures of
less than 4 mbar, ice can form and extend the
evaporation time.
At a pressure of 6 mbar, ice crystals are not formed
and the time required for evaporation can be
reduced by up to 30%.
Mixtures of water and methanol in deep well
microtitre plates however, respond entirely differently
as shown by the graphs shown on the next page.
At full vacuum, a reasonable evaporation rate is
achieved whilst at 8 mbar; the time required for
evaporation is increased significantly.
When evaporating 40 ml fractions in 24 x 150 mm
glass tubes or larger volumes in beakers, typical
evaporation times for water - acetonitrile mixtures
can be in excess of 8 hours.
A reduction can be achieved by setting the
SampleGuard control temperature to 60 degrees
centigrade for a defined period.
Provided the period was not excessive, the sample
temperature is likely to remain below 40°C, even
though the Coolheat lamps remain on as result of
evaporative cooling.
After this period, a second or a number of
successive runs can be linked at reduced
SampleGuard temperatures and different pressures.
Some experimentation would be necessary to
ensure that safe sample temperatures are not
exceeded.
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