Genevac HT-8 & HT-12 Series II Evaporating Systems
Page 58 of
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04-4541
Issue 1-9 – June 2008
When not to use Auto-Defrost and Drain
There are certain circumstances when Auto-Defrost and Drain should not be used. This is in order to protect
your system and/or your samples from solvent damage. Do not use Auto-Defrost and Drain in the following
circumstances:
•
Evaporation of TFA - intermediate (short) defrost and drain is permitted. Full defrost and drain at the
end of the method should not be done if there is residual TFA in the condenser. Perform a manual
defrost for 10 minutes, manually terminate defrost, manually drain the system
•
At the end of a lyophilisation method – water vapour may travel back from the cold trap to the chamber
and cause the powders to collapse. Remove the samples first, then defrost and drain.
Drying HPLC Fractions
The best optimised evaporation method has the following stages:
1. First
Stage
- removal of the organic phase
a. Use Variable Dri-Pure™ to prevent bumping:
Ramp the pressure down from 175mbar to 40 mbar (acetonitrile) or 45mbar (methanol) in 20
minutes at high rotor speed (500g).
Control the pressure at 40mbar for Acetonitrile and 45mbar for Methanol - these control pressures
are chosen to keep the boiling point above 0
o
C (i.e. don’t freeze the water).
b. Auto-Defrost and Drain at the end of the stage – this will be a short defrost (just in case any small
amounts of water have frozen in the drain port) and will drain the organic solvent from the
condenser, allowing high vacuum levels to be achieved later on in the run.
c. Consult your local Genevac representative for advice on the evaporation time for this stage.
However, a good rule of thumb is that for 50/50 Acetonitrile water the overall length of this stage
should be approximately 1/3 as long as the length of stage 2 (which the system will determine
automatically).
2. Second
Stage
- removal of the aqueous phase
a. Control the pressure at 8mbar (which ensures the BP stays above 0
o
C and the water cannot
freeze)
b. Keep the rotor speed high (promoting good convection & hence heat flow in the solution)
c. End the method using “Heat Flow”, rather than specifying a duration for the stage.
3. Third
Stage
- drying the stubborn samples.
a. Run the system at Full Vacuum for 1 to 3 hours
b. Trial and error will be required to optimise this stage. Different compounds will require more of less
of this to reach final dryness, with highly polar molecules often taking longest.
c. Auto-Defrost and Drain at the end of the stage - this will be a full defrost and drain, as there are no
more stages to follow.
See appendix A for programming details.
Please contact your local Genevac representative for further details on run times, alternatively please e-mail
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