Rotary evaporation is the process of reducing the volume of a solvent by distributing it as a thin film across the interior of a vessel at elevated temperature and reduced pressure which promotes the quick removal of excess solvent from less volatile samples. Rotary Evaporators are used in chemical laboratories. This instrument uses evaporation to gently and efficiently remove the solvents from samples including many organic, inorganic, and polymeric materials. A simple rotary evaporator system was invented in 1950 by the chemist Lyman C. Craig. It was first commercialized by the Swiss company Büchi in 1957.

Choosing a Suitable Evaporator for Your Lab

How will sample type affect which evaporator is ideal?

The sample in question will play a key role in the evaporator setup. For example, if acids are being used, the system must be properly coated to prevent corrosion (especially on the pump), and will need proper ventilation. Solvents can damage rubber and plastic components, and should be protected against as well. Another important consideration is that different samples are condensed at different temperatures, and may require different cold traps: typically a -50°C cold trap is ideal for aqueous-based samples, a -85°C cold trap traps most solvents, and a -105°C cold trap is recommended for alcohols.

How are safety concerns addressed for evaporators?

Due to the nature of heating up aqueous samples, acids, and solvents, a variety of safety accessories can be used to ensure the safety of the operators. As glassware is under extreme pressure due to the vacuum pump as well as being heated, coated glassware can be used to ensure flasks don’t shatter during operation. Shields and protective hoods with ventilation can also help ensure operator safety. Some manufacturers offer advanced options, such as motorized lifts and shutoff procedures for power outages or if the heating bath goes dry.

What environmentally friendly options are available for evaporator usage?

For the condensing and collection of samples, many options exist. Condenser coils or cold fingers are generally paired with circulating tap water or dry ice. While these methods are adequate for the purpose, constant changing of water to prevent algae buildup can get wasteful, along with a constant need for dry ice. Many manufacturers now offer circulating chillers which can be attached to evaporators, allowing for highly efficient condensation without the waste associated with using tap water or dry ice.

How a Rotary Evaporator works?

The main components of a rotary evaporator or “rotovap” include a motor unit, a vapor duct, a vacuum system, a heated fluid bath, a condenser with either a coil passing coolant, or a “cold finger, a condensate-collecting flask and a mechanical or motorized mechanism. In a rotary evaporator, the motor rotates the evaporation flask or vial containing the user’s sample. Vapor duct is the axis for sample rotation, and is a vacuum-tight conduit for the vapor being drawn off the sample. The vacuum system substantially reduces the pressure within the evaporator system. The vacuum system can be as simple as a water aspirator with a trap immersed in a cold bath (for non-toxic solvents), or as complex as a regulated mechanical vacuum pump with refrigerated trap. A heated fluid bath, which is usually water, heats the sample. The condenser used in rotary evaporator can be simple or complex, depending upon the goals of the evaporation, and any propensities the dissolved compounds might give to the mixture. The condensate-collecting flask is located at the bottom of the condenser and it catches the distilling solvent after it re-condenses. The mechanical or motorized mechanism quickly lifts the evaporation flask from the heating bath.

Considerations before buying a Rotary Evaporator

Rotation speed range (rpm), vacuum (mm Hg), temperature, pressure (mbar) and condenser are key parts that should be considered when buying a Rotary Evaporator. You can decide on the type of Rotary Evaporator suitable for your application based on the size, type and sensitivity of the samples. For example, if the samples are acids, they require an acid-resistant system.

Safety precautions For Rotary Evaporator

Possible hazards include implosions resulting from use of glassware that contains flaws, such as star-cracks. Explosions may occur from concentrating unstable impurities during evaporation, for example when rotavapping an ethereal solution containing peroxides. This can also occur when taking certain unstable compounds, such as organic azides and acetylides, nitro-containing compounds, molecules with strain energy, etc. to dryness.

Users of rotary evaporation equipment must take precautions to avoid contact with rotating parts, particularly entanglement of loose clothing, hair, or necklaces. Under these circumstances, the winding action of the rotating parts can draw the users into the apparatus resulting in breakage of glassware, burns, and chemical exposure. Extra caution must also be applied to operations with air reactive materials, especially when under vacuum. A leak can draw air into the apparatus and a violent reaction can occur.

It is recommended to take precautions to avoid contact with rotating parts, particularly entanglement of loose clothing, hair, or necklaces. In such cases, a rotating mechanism can draw the user into the apparatus. In an incident like this, a user is subject to burns, sharps and chemical exposure. Extra caution must also be applied to operations with air reactive materials, especially when under vacuum. A leak can draw air into the apparatus and a violent reaction can take place.