Articles & Tech Notes

What’s So Special About TFA? 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. Firstly, it’s an acid. This means that if not handled with care, it will corrode components of a system over time. Next, it is quite volatile (with a boiling point / pressure characteristic pretty similar to methanol). In combination with other solvents it can present a quite “bump-prone” mixture Thirdly, (and perhaps most infamously), it exhibits “creep”. In simple terms, this means that liquid TFA can climb the sides of a vessel to the height that any TFA vapour reaches. What is more, it can carry with it dissolved compounds, which may then end up actually leaving the vessel. Fourthly, and particularly worryingly for users who run into this problem, it can seep through polypropylene (including some brands of 96 well microtitre plates). This is not evidence of a failure to seal the bottom of the well during moulding of the plate – it actually goes through the plastic itself, due to it having an extremely low surface tension. TFA in sufficient concentration will also attack silicone (both silicone rubber seals and the special oil in a standard Genevac Cole pump). Finally, it can soften a PTFE coating on an item that is exposed to liquid TFA for any great length of time.

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.

Scientists working at the Great Lakes chemical company site in Manchester, UK have an interesting approach to new product development. As well as developing their own new products, they are also responsible for analyzing their competitor’s products too. This branch of the giant US-owned company specialises in the manufacture of polymer additives and the analytical laboratory in Trafford Park, as well as providing analytical services to R&D and manufacturing, specialises in de-formulating their rivals’ products.

Many solvent evaporators are routinely sited inside fume extraction hoods because residual solvent vapour, remaining in the chamber at the end of a run, can expose the operator to unwelcome, and potentially harmful, odours when the system is opened. In many cases these situations can be improved significantly by simple changes in programming . “Odour reduction” adds a repeated vent and vacuum cycle to the end of a method, which purges the evaporation chamber of residual solvent vapours. Utilisation of this function may enable the evaporator to be sited on the open bench rather than taking up valuable fume hood space.