Has anyone got a suggestion for an alternative transition fluid to replace the now banned and unavailable halocarbons which have been used in critical point drying using either ethanol of acetone. I'm not sure I want to use amyl acetate as its a bit toxic and remains in the seals of the critical point dryer.

For Cambridge watchers, it's two degrees celcius and snowing
Patrick Echlin

If you get direct posts, would you please forward them to the listserver. I too, am interested in a substitute, and have not been very happy with the quality of the CPD material since we can't realistically use Freon TF. I am under the impression that even freshly opened alcohol, within a few seconds absorbs water, but it may be even more complex than that, such as miscibilities of alcohol and CO2.

We have had numerous suggestions such as drying the CO2 tank out before refilling at the supplier, but I am afraid that our supplier is not that cooperative. To go the the next better grade of CO2 the price per tank goes from $15.00 to $130.00, and the specified composition with regard to water improves only marginally (I believe from 0.2% water to less than 0.1% water). A rather pricey experiment. We have a drier in the CO2 line and condense CO2 gas into the chamber, rather than use a siphon tube but these do little to improve the quality. Peldri II does work slightly better than CPD but does seem somewhat material dependent, and is relatively more expensive. Lastly, it should be mentioned that we do a large number of samples in a Polaron Jumbo CPD, so we do go through a fair amount of reagents.

I have been reluctant to use anything thus far besides alcohol both from the point of view of flammability and toxicity. During the winter months, with low humidity, on release of the CO2 there is a lot of static discharges. Knock on wood, no ignitions yet, but I am concerned.

Any responses that appear or that you pass along will be appreciated. later

David Bentley
dlb@u.Arizona.EDU

We use acetone or in some cases ethanol straight through to the CO2 and for most purposes it works just as well. We increase the times a bit and make sure that the solvents are as waterfree as possible. If it is very critical you will need a molecular sieve to dry the solvent and also a water trap for the CO2.

We also tried dimethoxypropane some years ago. It works both for dehydration (it forms acetone and methanol when mixed with water) and subsequently as transition fluid. As I recall the result was about the same as with the normal procedure (dehydration with ethanol and Freon as transition fluid).

Stefan Gunnarsson
e-mail Stefan.Gunnarsson@devbiol.uu.se

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