A Rapid Method For Degassing Samples

We have developed a useful technique for degassing samples that does not require flame-sealing the sample tube. The method involves the use of single tip-off manifolds (ACE Glass). Manifolds for sample tubes with diameters of 5 , 8 , and 10 mm are available. The systems we use in our spectroscopic work are illustrated in the figure.

A sample for absorption or luminescence study is dissolved in nonaqueous solvent and placed in a fire-polished, 9-in., IO-mm NMR tuhe, and the manifold is attached. The stopcock is closed and the sample freeze-pump-thaw degassed by immersing the sample tuhe in liquid nitrogen, opening the stopcock to high vacuum, closing the stopccek, and thawing the solution. Since it is aelosed system, thawingshould be done carefully, gently rubbing the sample tuhe with fingers, warming from the top down. Otherwise, sample tubes may break. After three cycles, the sample is adequately degassed for most measurements.

For emission and excitation spectra, in the exam- ole eiven in the firmre. the Dewar assemhlv (Soex & ~ - - -- ~~~ ~ ~ ~

Fluorolog) was the sample comp&tgent of the spectrofluorometer, serving as a cell balder. An extension to the original cell compartment was machined to accommodate the sample tuhe and attached manifold. For excited-state lifetime mea-

l surements at room temperature, a cell block was machined with the appropriate diameter for the sample tuhe and for openings for beam entrance and exit. This should he long enough to provide ade- quate support far an otherwise top-heavy system. A second black was fabricated for sample-tempera- ture control by water inlet and outlet in the cell hlnrk i taelf~ ...... ..... ~.

This concept has wide applicability for spectral data acquisition. The Dewar assembly and cell - blockcan be designed to fit in the cell compartments J " O I W

Cdl oompartmartmt (1. 4. 1 4.7b h) of most spectrometers. Also, one can use this tech- nique in most areas of spectroscopy where the sam- ple is stationary. The apparatus i s simple to assemble and is as effective as other degassing methods but with less expense in the long run

because sample tubes can be reused. Although certain solvents, notably THF, attack the O-ring seals, we have found that properly sealed systems maintain their vacuum for up ta 24 h, offering ample opportunity to carry out most desired mea&riments.

This technique was developed on a research project funded by the Ofiice of Basic Research of the Department of Energy under grant DE-FG05-84-ER13263.

Randy Shaver, Shawn Van Wallendael, and D. Paul Rillema The University of North Carolinaat Charlone

Charlone. NC 28223

604 Journal of Chemical Education