The basic anatomy of a rotovap

All rotary evaporators have these fundamental components:

  1. Heating bath: the sample flask is lowered into the heating bath during operation. Temperatures are set dependent upon the sample being used.
  2. Condenser: as the sample heats, the vapor rises through the condenser apparatus to be cooled and collected.
  3. Collecting vessel: the vessel in which the condensed vapor collects.
  4. Rotating sample flask: flasks of various sizes and construction are available depending on your application.

Options to look for when purchasing:

  1. Programmable: different models offer a variety of preset modes, or the option to program your own mode.
  2. Remote controls: a wireless remote can be removed from the evaporator to take with you for adjustments away from the rotovap. Look for one with rechargeable batteries. If you are operating multiple evaporators, there may be options to individualize the different remotes to avoid errors when adjusting them. Finally, make sure the base unit has a paging function to find the remote, when you inevitably put it down somewhere and can’t find it.
  3. Vacuum pump: use a vacuum pump for ventilation instead of a water aspirator or house vacuum for better control, it’s also chemically inert, and quieter.
  4. Temperature range: check if the rotary evaporator accommodates the temperature range you need.

Heating bath features for optimal evaporations:

  1. Type of heating medium
    • Water: has a top limit of 100°C, at sea level.
    • Silicone oils: can be used to adjust the liquid bath temperature to between 150-210°C.
    • Glycol based liquids: for temperatures up to about 170°C are safer than oils, because water that hits the hot liquid doesn’t foam and spit. It also cleans up with just water.
  2. Adjustability
    • Position: heat bath position can be adjusted on some models to help accommodate different sample flasks.
    • Scale: some models will have a fill line in the bath corresponding to the sample flask you will be using. This prevents over- and under-filling of the bath.
  3. Features for cleaning
    • Shaped vessel: a pouring spout on the heating-bath vessel allows for easy removal of the medium.
    • Handles: to help when moving the bath or emptying the heating fluid.
  4. Refrigeration: for heat sensitive samples.
  5. Bump controls: Bumping is the loss of sample through the solvent recovery path due to the rapid heating or vacuum application
    • Splash or bump traps: to prevent sample loss if there is any bumping.
    • Vacuum controller: helps prevent bumping altogether using automation or vacuum gradients.

Condenser features for best performance:

  1. Application types: check with your manufacturer for the types of applications their condensers are made for and match them to your application. Applications include distillation, drying, concentrating, reflux reactions, recrystallization, and Soxhlet extraction.
  2. Cooling mechanism and temperatures: choices could include water from a tap, dry ice, another cooling liquid, or a cooling mixture (such as dry ice and ethanol).
  3. High throughput: check with your manufacturer if the condenser is capable of handling high throughput processes.
  4. Size: not all condensers will fit in all spaces

Collecting vessel features to consider:

  1. Flask lift: choose between a manual or motor lift, which can be important for handling large flasks and for safely raising and lowering the flasks at the appropriate speed.
  2. Variety: investigate what collection flask options your manufacturer has and if they would be appropriate for your application.

Sample flask features to look for:

  1. Refill valve: some manufacturers have an optional refill valve to allow you to add sample during processing so you don’t have to remove and replace the sample flask.
  2. Sample size: sample flask sizes can range from 5L to 50L, so shop around to find the size that will work for your process.
  3. Clips and clamps: some models have clips designed for easy attachment and removal of the sample flask.
  4. Variety: as for collection flasks, investigate if the manufacturer has flasks appropriate for your applications

Optional features for improved safety:

  1. Protective shield: a rotovap should be operated in a fume hood for safety, but if your heating medium temperature is under 90°C, some manufacturers offer a protective shield to allow benchtop usage.
  2. Sensors: sensors are available to monitor condenser heat, pressure, vapor temperatures, vacuum levels, bumping, alerts when the collection vessel is full, or foaming.
  3. Instruction manuals: all manufacturers now have their manuals online. Download them and see how easy their instructions are to follow and if they are comprehensive enough for your applications.
  4. Ergonomics: check to see if the manufacturer has considered ergonomics in their design.