**3. Concentration techniques for reducing the solvent volume**

Once the analytes are diluted in the presence of a large volume of solvents during the extraction processes, they should be concentrated to analyze by instrumental methods as GC. If the amount of solvent to be removed is not very high and the analyte is nonvolatile, the solvent can be vaporized by a gentle stream of nitrogen gas flowing either across the surface or through the solution. But when a large volume of solvent should be removed, a rotary vacuum evaporator is used. In this case, the solution is placed in a round-bottomed flask which put in a heated water bath. A water-cooled condenser is attached at the top of flask to condense the evaporated solvent, and it distils into a separate container. Then, the flask is rotated continually to expose maximum liquid surface to evaporation. It should be noted that evaporation should stop before the solution reaches dryness.

For achieving smaller volume, e.g., less than 1 ml, a Kuderna-Danish concentrator is used. In this case, the solution is slowly heated in a warm water bath until the necessary volume is obtained. Also, an air-cooled condenser provides the solvent reflux [2].
