Abstract: In the drying of solvents-containing material in a vacuum concentrator and which involves condensation of evolved solvents in a cold trap, simplified and inexpensive flow blocking devices are provided intervening an outlet of the cold trap and an inlet to the vacuum pump with which the concentrator is evacuated. The flow blocking practiced allows cryopumping effect to ensue between the concentrator and cold trap such being the agency by which solvent vapor outflows from the concentrator and is recovered by condensation thereof in the cold trap. Near complete solvent recovery can be achieved and carryover of solvent to the vacuum pump is reduced to insignificant measure. In one form, flow blocking is attained by use of a simple pressure differential valve.

Abstract: A solvent-containing biological material specimen is dried in a vacuum chamber with solvent evolving during the drying cycle being condensed in a refrigerated cold trap. During the drying cycle, communication of the drying chamber with the vacuum pump with which the chamber is evacuated, selectively is established or interdicted in response to raising or lowering of the vacuum condition in the chamber with respect to an initially set predetermined vacuum condition. Evolving of solvent from the specimen proceeds during interdiction by way of "cryopumping" due to the differential in pressure between the chamber and the refrigerated trap. Thus maximized solvent recovery in the trap is achieved, and carry over of solvent to the vacuum pump wherein its presence would be contaminating of the pump oil is for practical purpose eliminated.