Today’s rotary evaporators often handle multiple samples at once, but each must be processed without being impacted by the others. Scientists must make sure that there’s no cross-contamination. That requires careful control of the airflow. Users must also keep their systems in excellent condition. It’s essential to keep the needles clean; if holes are plugged up in the needles, wells won’t dry down. In processes that involve acids, the needles can get corroded and plugged. Some systems use stainless-steel needles; others use polytetrafluoroethylene, so it is essential to choose the proper needles for your application. If a system includes a regulator, as many do, it must be maintained as well.

Bumping and foaming are problems that commonly arise during evaporation and can lead to sample loss and contamination. The primary culprits are applying too much heat, too much rotational speed, or too much vacuum to a particular application.Bumping occurs when the sample boils and bubbles rapidly, causing the product that is being concentrated to splash out of the vessel. Foaming, on the other hand, results from surfactants, which can be present in natural extracts as well as artificially made products. Foaming is a slower process than bumping, and foam tends to stay inside the evaporating flask for a longer period of time.

The traditional way to avoid bumping during evaporation is through visual inspection—simply watching the samples EVAPORATORS INCUBATOR RESOURCE GUIDELab Manager 2 018LabManager.com6and adjusting the vacuum pressure so that bumping doesn’t occur. Foaming cannot be avoided per se; it can only be reduced. The most common method to minimize foaming is to open and close the stop cock whenever foam appears. Another way to diminish the issue is to slowly apply vacuum.”

Along with these methods, several products are available that can reduce sample loss and contamination when bumping and foaming occur, help eliminate bumping altogether, and minimize foaming. To specifically address the issue of foaming, one may use an anti-foam agent, a large flask, or a dedicated glass condenser, which provides much more space for foam to expand. A simple glass foam brake can help keep foam from entering the receiving flask. A bump trap, which is a secondary flask that is smaller than the main flask, is also often used during evaporation. This additional flask is placed right above the main flask so that if bumping occurs, the sample will get caught in the bump trap before getting drawn into the rest of the rotary evaporator or condenser. Putting a bump trap in line doesn’t reduce the bumping, but it does prevent the sample loss.

Vacuum controllers get closer to the root of the problem. By controlling the speed of the pump, these devices can drastically reduce or eliminate the likelihood of bumping. Automatic features are available to sense the vapor pressure of the solvent and use that as a set point. Then there are foam sensors, which detect the foam inside the evaporating flask and aerate the system slightly to make sure that the foam collapses. The foam sensor allows automatic, unattended distillation of foaming samples.

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