Wayne M. Moreau, Theodore A. Tyler, and Karl Weirs
Northeastern University Boston, Massachusetts
I I
Transfer Apparatus for Degassed Solutions
In many liquid phase photochemical experiments, the rigorous exclusion of oxygen is necessary. This is usually accomplished by subjecting solutions to repetitive liquid nitrogen freeze-thaw cycles on a high vacuum line. When the photochemical change is completely reversible in the dark, a given sample may be used for many experiments. However, most photochemical reactions are irreversible, and in these cases repetitive experiments require the preparation of many individual samples. This is extremely time-consuming. Also, if a number of d i e r e n t sample cells are employed, slight differencesbetween them and non-uniformsolvent loss lead to poor reproducibility of results. We have developed a sampling apparatus which overcomes these problems, and which has been successfully used in flash photolysis and spectrophotometric kinetic studies. All glass construction is preferred since the greaseless O-ring seals recommended by Hanrahan1 are susceptible to slow attack by solvents such as tetrahydrofuran. The degassing bulb2 A (see figure) is filled with solution by means of a narrow funnel which is inserted into the ring-sealed tube D. The assembly is connected to an "L"-shaped arm of the vacuum line (ball and socket joints), so that bulb A is held in a vertical position for efficient freezing. Degassing is carried out in the usual manner with magnetic stirring during the thawing cycles. If desirable, the solvent can be trap-to-trap
This apparatus was developed in the course of research sponsored by the U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research (Contract AF19(628)3836), and by the Department of Health, Education, and Welfare, Public Health Service (Grant RH00302-02). HANRAHAN, R. J., J. CKEM.EDUC., 41, 623 (1964). "Pyrex" Kjeldahl flasks make reliable degassing bulbs.
distilled between flasks A and B. After degassing, the assembly is sealed a t E, and solution is poured into the reaction vessel C by tipping. After the experiment, the contents of C are transferred, again by tipping, into the waste reservoir B. The reaction vessel is then rinsed with a small quantity of fresh solution and is refilled for the next run.
w Tronsfer orsernbly
m a s h e d to vacuum line.
In one application of the apparatus, Cis a cylindrical flash photolysis cell (14.0 cm path length, 25 ml capacity), and vessels A and B can each accommodate 500 ml of solution. This quantity suffices for 22 flash experiments, which would have required the same number of sample preparations. A smaller version of theassembly is suitable for repetitive photochemical electron spin resonance experiment^.^ RABOLD, G . P., BAR-ELI,K. H., REID, E., J . Chem. Phys., 42, 2438 (1965).
AND
WEISS, K.,
Volume 43, Number 8, Augurt 1966
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