The solution is two fold;
1. If your gel dryer allows you to program in a temperature ramp, start with
a higher temperature for 10 minutes or so and then ramp the temperature down
to 35 C for the remained of the drying cycle. This effectively reduces the
vapor pressure of the trapped solvents and reduces the likelihood of surface
eruptions. If your gel dryer is a manual version you are the ramping
controller or use very low temperatures to slow down the solvent extraction.
The down side is longer drying times.
2. The vacuum system needs to maintain a constant vacuum ( negative
pressure ) during the drying process. Small changes in systemic pressure
coupled to the addition of heat ( as described above ) cause the mass
transport of the solvents to exceed the maximum transfer rate of the solvent
through the dried surface of the gel, resulting in an eruption. With some
vacuum systems the trap is the culprit. If the trapping temperature is not
cold enough to condense the solvent vapors emitted by the gel many of the
solvents gel are passing into the vacuum pump raising the vapor pressure of
the oil ( this is assuming the use of an oiled fill vacuum pump ) and
thereby raising the systemic pressure of the system. If you are using an oil
free vacuum pump you may need to install a bleed valve between the gel dryer
and the pump to keep the raise the vacuum pressure to a value that will
remain stable during your drying cycle.
I'm sorry that this has become a treatise on gel drying but as you can see
there is a fair amount of interaction between the components of the system.
The proper approach to the process will insure a consistently good gel
recovery with reasonable drying times.
Steve Mitchell
ATR, Inc.