Roger E. Rondeau Air Force Materials Laboratory Wright-Patterson AFB, Ohio 45433
A Technique for Degassing Liquid Samples
In many photochemical and radiation chemical studies as well as in some nmr and esr observations, special care must he taken to remove dissolved air from the liquid sample. The two usual methods of degassing liquids involve either freezepump-thaw cycling or flushing with an inert gas. Both methods are rather time-consuming and relatively inefficient-especially when the sample is contained in a long, narrow tube as in nmr and esr work. The technique described and depicted here is much more efficient than freeze-pump-thaw cycling and much faster than gas flushing. The rapidity of the method depends on the volatility of the liquid. The tube containing the sample is attached to the bottom of a borosilicate glass cold trap (with an O-ring adapter or with a greaseless joint, etc.) and frozen with liquid nitrogen, or some other appropriate coolant. With the sample frozen, valve A is opened and the air above the sample is removed. After this preliminary pumping, the valve is closed and the liquid nitrogen is removed from around the sample tube and poured into the cold trap. Condensation of the liquid sample occurs as a thin layer along the bottom of the spherical
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cold wall. The last t r : w of air that was previously illcxtrieably trapped in t,hc liquid column can now be quickly removed by pumping (111 the thin, exposed layer of the sample. After pumping, tho valve is closed and . the liquid nitrogen is removed from inside t l ~ c VAC cold trap by blowing into it with an air hose. The sample is then allowed to drip hack into the tuhc A by liquid nitrogen pumping (and gravity) where it is sealed under vacuum. Tho insert depicts a simple ball and socket connecting tube fabricated with a ring seal and drip tube to prevent the returning liquid from coming in contact with Sample the grease on the joint.
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