Articles & Tech Notes

This month, we are discussing a complex problem that is becoming more and more prominent because of the chemistries specified and the ways of working that are being adopted by many users of evaporation equipment. We’re principally concerned with mixtures in which there is one volatile component and one high boiling point solvent. An example might be methanol /DMSO, or THF/pyridine. What's more, the two solvents don’t have to be within the same sample. A rack of tubes where each tube contains a different single solvent, will also exhibit the effect described below. Frequently a user who wishes to remove methanol/DMSO will not even mention the methanol when specifying the application, because methanol is “easy” and it’s the DMSO that is considered the challenge. However, this overlooks a rather important technical issue that we will deal with here.

TFA (Trifluoroacetic acid) has several properties that make it very important that you take the right precautions when evaporating it, in order to get optimum performance and prevent damage.

Did you ever calculate the value of the samples you put through your evaporator? In many cases, the value of a month’s throughput is more than the value of the instrument itself. We’re not talking about the value added by the evaporation step, but all the value added up to now in getting the samples this far. Why is this figure important? Because if your evaporation step were to damage your samples, and you had to remake them, this is how much money you would be throwing away. Now, there’s no reason why you should do anything to damage samples in your evaporator, provided you use it correctly. The point we’re making, though, is that your primary focus must be to get your samples through the process intact, and uncompromised. Getting them dry fast should be the second, not the first, priority. Here we’ll be dealing with the various aspects of sample protection, and the things to watch out for.

Changing sample vessel format is an area of Discovery research that can cause problems: sample tracking, sample loss and robotic referencing are among the many drawbacks of having to perform a transfer step. Genevac set out to attempt to “automate” the transfer step within their evaporation systems and developed several concept designs. The final iteration of this is now launched as the SampleGenie™ system, shown in figure 1. SampleGenie comprises a specially designed large volume glass flask that securely seals to a small storage vial, dramatically increasing its capacity. This allows a purified or other large volume sample to be evaporated directly into the small vial. The whole assembly is loaded into the Genevac HT or EZ-2 evaporation system and using a pre-written method evaporated to dryness. SampleGenie guides the compound into the storage vial directly, thus avoiding the costly transfer step that has traditionally been the cause of problems, and reduces the overall process time by between 0.5 to 1 day in the typical laboratory. If an amorphous anhydrous powder is required at the end of this step then an HT series evaporator with LyoSpeed™ can be used to concentrate the large volume into the vial, and then Lyophilise the remaining volume to leave a powder in the vial. A concentration only version is also available for users requiring a wet sample.