Evaporation with Nitrogen Gas

A very convenient method for removal of final solvent traces is the concentration of fhe lasf 0.5 mL of a solution by evaporation with a gentle stream of nitrogen gas while the sample is warmed in a sand bath. This process is usually done at a hood station where several Pasteur pipets can be attached to a manifold leading to a source of dry nitrogen gas. Gas flow to the individual pipets is controlled by needle valves. Always test the gas flow with a blank vial of solvent. 

Ruekberg described an alternative way to remove solvent from solutions of compounds fhaf are not readily oxidized. The setup includes an aquarium air pump, a pressure safety valve and ballast container, a drying tube, and a manifold. Blunted hypodermic needles are used in place of Ftisteur pipefs. 

The sample vial will cool as the solvent evaporates, and gentle warming and agitation of fhe vial will thus help remove the last traces of the solvent. This avoids possible moisture condensation on the sample residue, as long as the gas itself is dry. Do not leave the heated vial in the gas flow after the solvent is removed This precaution is particularly important in the isolation of liquids. Tare the vial before filling it with the solution to be concentrated constant weight over time is the best indication that aU solvent has been removed. 

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