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8333336 
Journal Article 
Development of a high-performance evaporating apparatus for organic and biological samples in test tubes 
Kadono, T; Okamoto, J 
1988 
38 
35-49 
Japanese 
Evaporating solvents from biosamples after their extraction by organic solvents is often an essential procedure in analyses of medicines and their metabolites in biological fluids and tissues. Various types of evaporating apparatuses are commercially available, but their performance and handling characteristics are not always satisfactory for the analytical purpose intended. In using such equipment, we have often found the evaporation process to be too time-consuming resulting in decomposition of the thermally labile compounds to be analyzed, encountered sudden boiling (bumping) of the solution, and sometimes found the samples contaminated with plasticizer that dissolved from the plastic tubing (Unitube) due to exposure to recycled solvent. To overcome these problems, we developed an evaporating apparatus which can be adapted for various analytical demands and can handle a relatively large number of samples per cycle. Our evaporating apparatus is equipped with four special devices: (1) a warming hood for heating the solvent vapor evaporated from test tubes so that it does not liquefy and flow back; (2) adaptors capable of simultaneously evaporating sample solvent in a large number of test tubes (maximum 5 ml x 24 tubes); (3) a cooling device capable of reversibly changing the direction of vapor passage depending on the boiling and freezing points of solvents, in order to efficiently cool and liquefy the vapor from any solvent by use of a dry ice/acetone coolant; and (4) a solvent trapping device with which bumping during the evaporation process can be prevented by an easy control method and which can easily be handled to discard a relatively large quantity of trapped solvent. Our apparatus enables efficient evaporation with a high level of safety even for radioisotope-labeled samples. Performance evaluation tests were done for various solvents such as diethylether, n-hexane, acetone, benzene, isopropanol and water, to compare the treatment times needed for evaporation and the trapping yields. The results showed that even in the case of diethylether, which is usually difficult to completely trap, 24 x 5-ml sample solvents could be evaporated and trapped within 5 minutes in a high trapping yield of 97%. And even in the case of less volatile solvents such as water, all 24 x 2.5-ml sample solvents could be evaporated to dryness within 20 minutes at a water-bath temperature of 40°C and a vacuum level of 11 mmHg. We also developed a device for introducing an inert gas to prevent oxidation of labile compounds during evaporation. By incorporating this device into the apparatus and conducting the evaporation under nitrogen gas flow, for example, we could improve the recovery of the air-oxidizable compound S-312 from rat plasma. Thus, the present apparatus provides one of the most suitable means for rapidly evaporating a large number of sample solutions without their decomposition. Sixteen evaporating appratuses of this type are now in use in our laboratories.