<Li> A mechanical or motorized mechanism to quickly lift the evaporation flask from the heating bath . </Li> <P> The vacuum system used with rotary evaporators 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 . Glassware used in the vapor stream and condenser can be simple or complex, depending upon the goals of the evaporation, and any propensities the dissolved compounds might give to the mixture (e.g., to foam or "bump"). Commercial instruments are available that include the basic features, and various traps are manufactured to insert between the evaporation flask and the vapor duct . Modern equipment often adds features such as digital control of vacuum, digital display of temperature and rotational speed, and vapor temperature sensing . </P> <P> Vacuum evaporators as a class function because lowering the pressure above a bulk liquid lowers the boiling points of the component liquids in it . Generally, the component liquids of interest in applications of rotary evaporation are research solvents that one desires to remove from a sample after an extraction, such as following a natural product isolation or a step in an organic synthesis . Liquid solvents can be removed without excessive heating of what are often complex and sensitive solvent - solute combinations . </P> <P> Rotary evaporation is most often and conveniently applied to separate "low boiling" solvents such a n - hexane or ethyl acetate from compounds which are solid at room temperature and pressure . However, careful application also allows removal of a solvent from a sample containing a liquid compound if there is minimal co-evaporation (azeotropic behavior), and a sufficient difference in boiling points at the chosen temperature and reduced pressure . </P>

Why is rotary evaporation conducted under low pressure
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