If you're trying to lyophilize a substance with oil, your output will never be an entirely solid powder. The oil in the sample will sublimate first and leave behind a slicker consistency, but this isn't a deal-breaker. A reduction in drying chamber pressure will shorten the lyophilization time but increase the release of volatile compounds.
All Posts. Jan 1, The following tips aim to help you successfully adopt organic solvents in your lyophilization workflow. Many organic solvents have a low freezing point, often well below that of the condenser surface temperature.
Four key questions can help determine if and how a solvent can be freeze-dried:. How can the solvent be frozen? Find the most appropriate method that can reach a low enough temperature so that the sample is fully frozen. At which concentration can the solvent be frozen?
Determine if the solvent must be diluted prior to freezing. Can the condenser collect the solvent? Will the sample remain in a frozen phase during the process? Evaluate if you can maintain a pressure that is low enough to keep the sample frozen. In contrast to aqueous samples, organic solvents are tricky to freeze and require dilution prior to freezing.
Chemists might need to use liquid nitrogen for the solvents to reach a low enough temperature. Moreover, due to the low freezing point of organic solvents see table above , the condenser temperature might not be low enough to completely capture the solvents.
Instead, the organic solvents liquify in the condenser or leave the system through the pump as vapor. Because of this:. A scroll pump is recommended for all freeze-drying applications involving organic solvents. The low freezing temperature and triple point of the organic solvents makes it difficult to evacuate the system fast enough and to maintain a low enough pressure to avoid solvent melting, even at ultimate vacuum.
For diluted solutions, it is rather common to see solvents melting and evaporating, while water remains frozen. Whether this is problematic for you depends on your sample requirements. If the solvent amount is too high, the system will not be able to maintain the required pressure and everything will melt and evaporate.
The process must be terminated at this point. Example of compatibility of common organic solvents with Lyopvapor L It might be challenging to find a car charging station or bioethanol fuel station, but it might be worth the trouble in the long run.
Same with using organic solvents in lyophilization. The ends might just justify the means. That's not to say that you can't just try it with a normal vacuum pump, of course. Thanks for your idea, but.. I don't know the "high' vacuum you mean. I have tried mmHg at k, but it's not working.
What is the exactly value about the vacuum degree? For the few samples that do not dissolve well in 1,4-dioxane, two methods have been used successfully: 1 Samples are redissolved in a small amount of methanol 2—3 mL ; then water approx.
The following range of solvent mixtures and volumes was developed and selected for samples based on the researched knowledge of sample solubility:. Solvent volumes were measured using a 1. Sufficient solvent must be used to enable good freezing, since samples are being frozen using vacuum alone.
Sample volumes were halved under vacuum and samples were completely frozen after 20 min. The samples were lyophilized in 4-mL vials held in microplate holders that insulated the samples from too much heat. Trials were carried out with and without a heating stage.
Both settings produced lyophilized samples, but occasionally some powder was seen to drift out of the tubes and into the evaporation chamber.
Cross-contamination by fluffy samples that could have been blown around was avoided by restricting the vent inlet and covering the samples with pierced plastic paraffin film. Samples were tested using proton NMR and were found to be free of residual solvent and cross-contamination. Care is required when removing the film.
Cross-contamination can also be eliminated by applying a higher g -force. When handling new chemical entity NCE drug or agrochemical libraries and arrays, it is common practice to dissolve each NCE in DMSO, making it possible to process them with liquid handling automation. Many samples form a gum, oil, or waxy solid and do not truly dry, although complete drying is essential or inaccurate conclusions may be drawn. Ideally, a method to freeze-dry DMSO was required so as not to disrupt the sample work flow.
Any work done outside of this work flow would be highly disruptive. The holder was then frozen in a bath of liquid nitrogen and transferred to the Genevac HT evaporator for drying under vacuum.
Samples were dried at full vacuum for 7 hr. Seven out of nine samples dried fully, although two only dried to a wax. The powdered nature of the resulting samples enables safe storage. Abeysena is Applications Chemist, and Mr.
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