Convenient, Degassable, Reusable Tubes for "Merry-Go-Round" Photochemistry and General Vacuum Line Applications 11%. ohotochemical reactors' often re~luiresthe vacuum line overations of freeze-pump-thaw de. of "merrv-ro-round" . ~, n gasaing and flame waling ofsamples in glass iuhes. Excesswe expenditures c,lcnmpl~s,t m e , and yuud will in many quarters u.hm haw wrhniqucs sere nttcrnptnl in imrlprgmduste research projrrLs led us togepk >mprwmrnen&.\FP have now found :I unique V B C U U iral ~ i l ~ ~ i l ~ l ~ l r r o m m e rnhiclt t i a l l ~u e have used make reurahlr $ample tulres The ruheq have hwn exceedingly efficient in our applications and may have some general utility. As shown below, the tube in position n is sealed by two O-rings, one above and one below the two holes in the sliding elass stovoer. In wsition b the tube and the space between the O-rings may be evacuated. On return to position a , the lower the lower O-ring without leakagesince a vacuum exists above and below the O-ring. b e ~
~~~~
~
threaded tube
170 x 15 m m
position b
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basition a
A batch of six samples in tubes of this type may be degassed to residual pressures of 10-"on in 30-45 min. Leakage into degassed tubes was not detectable in periods of 2&48 hr. The tubes may be used with no lubricant by experienced hands, but we have found it expedient to lubricate the sliding stopper with a very thin film of silicone grease. The O-ring seal is secure when only slightly compressed; undue tightening may result in breakage of the tube or difficulty in moving the stopper. The tubes make excellent containers for irradiated solutions during workup or analysis since the seal does not leak, and the entire stopper assembly is easily unscrewed to allow direct access to the contents with a pipet or syringe. Graded seals allow use of the threaded borosilicate top with quartz sample tubes. In actual use, tubes of the dimensions shown containing4 ml samples are attached to the vacuum line through heavy wall tubing. The line stopcock is opened to the tube in position a , and the sample is frozen slowly from the bottom upward in liquid Nz, taking care toavoid cooling the O-rings somuch that leakage occurs. The tube is raised to position b until the pressure stabilizes, and then returned to position a. The contents are thawed immediately by bathing the bottom inch or two of the tube in methanol, which is applied with a rapid up and down motion of the container. Since most solvents expand when melted, the tube will often break when thawed by means other than that described. The partially melted plug will often rise and be retained in the cold center of the tube, where it should be melted on one side only using the heat from one's hand. When the plug drops to the bottom again, thawing may proceed rapidly using a water bath. Degassing cycles are repeated as necessary, whereupon the line stopcock is closed and the tube in position a is removed from the line. We are aware of a few other applications of these tubes or the vacuum seal by itseK2 These include use for isolating samples under vacuum or an inert gas, reactions involving gaseous or other radioactive materials, and reactions which may involve modest accumulation of pressure.
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Moses. F. G.. Liu. R. S. H.. and Monroe, B. M., Mol. Phatachem., I, 245 (1969);commercial models are now available. Information on parts and designs may be obtained from the Ace Glass Co., P. 0.Box 688,Vineland, NJ 08360.The author. appreciates the timely suggestions and assistance of Hugh Bowe and the late Maurice Anderson of the Ace Glass Ca. Grinnell College Grinnell, Iowa 50112
Gene G. Wubbels
i
Volume 54, Number 1, January 1977 / 49
