Concentration of an extract to a small volume is often necessary prior to spotting on thin layer plates. In many instances, the extract is concentrated to a desired volume, transferred to a suitable container and final evaporation accomplished by a stream of air or nitrogen. A known volume of solvent is then added and the sample is ready for spotting. Often the vessel used for the final evaporation step is not suitable as a storage vessel and the sample must be transferred again. The following described method is considerably more rapid than air drying, it eliminates the necessity of transferring the sample to a storage vessel and may be accomplished with a minimum of expensive equipment.