Evaporation of Chromatography Fractions Simplified Evaporation of chromatography fractions on a rotary evaporator requires either a large "fleet" of costly J flasks or many inconvenient transfers. A most satisfactory solution to the prohlem is t o collect fractions in ordinary Erlenmeyer flasks and connect these to the 3 joint of the evaporator through an inexpensive (-$0.10) cup-shaped polyethylene stopper (Nalgene, eat. No. 6190). Size 1will adapt 25- and 50-ml flasks t o a $19138 joint on the evaporator, and size 4, 125-ml flasks t o a 324140 joint (or a hushing adapter on the smaller joint). Before first use, several small holes are made with a stout needle around the center of the bottom of the stopper to provide passage for the vapor. The rest needs no explanation. Aside from the great saving of east or inconvenience, this technique (which need not he restricted to chromatography) offers several other important advantages: (1) the restriction of vapor flow by the holes prevents the solution from boiling up violently when vacuum is first applied, yet permits orderly evaporation; (2) the stopper will catch foreign pxticles which often tend to drop from the evaporator into the solution; (3) condensation of solvent vapor in the evaporator is far less likely to occur hecause of the throttling action of the stopper, and it is even less likely that any condensate will actually return to the flask;(4) it is far easier to clean the stopper than the entire evaporator head; and last hut not least, (5) the flask is always easy to separate from the stopper, which is often not the case with a J flask on the 3 joint. George Vogel Boston College Chestnut Hill, MA 02167
Volume 59
Number 1
January 1982
69
