Evaporators - "Rotary Evaporators"

For decades, rotary evaporators have been staples in labs and industries performing chemistry, including labs in the chemical, environmental, materials, life science, and forensics industries. Key applications include sample concentration, solvent recycling, extractions, and separation of solvent mixtures.

In their simplest embodiment, “rotovaps” consist of a temperature bath, rotating flask, condenser, collection flask, and vacuum source. Solvent distills from the sample under the combined effects of heat and vacuum, and collects after condensation in the collector. Recovered single-phase organic solvents may be dried and re-used; binary, tertiary, or quaternary solvent mixtures are also re-used but may need adjustment for composition.

Water is the fluid of choice for the bath, but some laboratories use oils to reach heating temperatures of up to 180°C. Several choices are available for the condenser coolant. Chillers provide more precise cooling, greater control over condensation, a greatly reduced environmental footprint, and overall are less expensive to use than water. High-efficiency trapping of low-boiling solvents is achieved with a “cold finger” charged with dry ice and acetone.

Vacuum is probably the broadest rotovap option. At one time, water aspirators were the most common vacuum sources. That practice has gone by the wayside due in part to environmental concerns related to solvent vapors venting down the drain.

The next most common source is house vacuum, which is limited but inexpensive and reliable. Users typically insert a Woulff bottle or cold trap between the vacuum spigot and the rotovap, to trap volatiles the condenser missed and protect the house vacuum system.

Increasingly, users employ vacuum pumps to achieve reproducible and rapid solvent removal. The vacuum must be applied carefully, however, to avoid problems.

Users are now turning to more sophisticated vacuum control, which Kristof O’Connor, product manager at Heidolph Brinkmann (Elk Grove Village, IL), describes as “probably the number-one improvement in rotary evaporators over the past two decades.” Control became necessary, he says, because “vacuum pumps are very stupid machines. They try to achieve as high a vacuum as they can, as quickly as possible, which often results in bumping and foaming.”

Newer rotovaps may incorporate thermocouple-controlled operation, in which a pump integrates with a controller and a thermocouple located near the condenser coils. As the coil temperature rises through heat transfer between the condenser and the evaporated solvent, the vacuum is bled out through valving to maintain steady distillation. Another technique, known as “RPM” control, speeds or slows the pump’s inner workings to control the delivered vacuum.

Systems integration is also important in rotovaps. In such an arrangement, the main components of the evaporation solution are fully integrated with respect to parameters and control. The benefits include: up to 75 percent reduction in energy consumption, reduced heat emissions in the lab, optimized distillation capacity, and increased process safety. Buyers should consider several vacuum and condenser cooling options before buying a rotovap. Cooling method, which dictates the type of condenser used, should be decided based on the expected solvent load. More vigorous cooling is demanded for high volumes, rapid distillation, and very low-boiling solvents.

Rocket

Evaporates samples quickly and with a precise temperature control
Dries or concentrates as many as six large volume flasks or 18 ASE tubes simultaneously
Provides excellent recoveries of even the most volatile analytes
Dri-Pure® technology prevents solvent bumping and cross contamination inherent with rotary evaporator and other vacuum evaporation systems

Genevac
www.genevac.com

RapidVap Vertex

Microprocessor-controlled heater supplies heat to the block and is programmable from 30° C to 100° C in 1 degree increments
Up to 50 samples may be processed at once for maximum throughput
Nitrogen blow down reduces the partial pressure directly over the liquid to speed evaporation and helps remove the solvent as it evaporates

Labconco
www.labconco.com

Centrifan PE

Simple, robust and safe for users and samples
Easy-to-use and low cost of operation
Less expensive than typical vacuum concentrators
Replaces polluting nitrogen blow-down set-ups
Dries six 20 mL vials at once

Modular SFC
www.modularsfc.com

MiniVap™

Removes volatile organic solvents from HPLC fractions collected in 24- or 96-well microplates
Installation just requires connection to a standard gas supply and standard mains socket
Incorporates advanced evaporator head technology which directly injects heated nitrogen into each microplate well simultaneously

Porvair Sciences
www.porvair-sciences.com