R. P. Harpur McGill University Macdonald College P. O., Quebec, Canada
A Simple Valve for Burets Chromatographic Columns
A
recent article by Crawfordl outlines some of the difficulties encountered when titrating with bases. The control of the flow of chlorinated hydrocarbons through chromatographic columns, especially under pressure, is an even more difficult problem. The commercial valves available are expensive, require special glassware, and some are liable to leak with organic solvents under pressure. A new form of flexible tetraflnoroethylene tubing (Annealed, Teflon, Pennsylvania Fluorocarbon Co., Inc.), which has recently appeared on the market, may he employed to construct the device described below. When used with a buret it is possible to make titration additions of 0.005 ml, and with chromatographic columns it is easy to control the flow of chloroform under a pressure of 5 lh Since t.etrafluoroethylene is reported to be resistant to all but molten alkali metals or fluorine at elevated temperature^,^ this simple valve may find many applications. The annealed tetrafluoroethylene tubing (4.5 mm i.d.) is pushed as a tight fit over glass tubing and requires no clamps or wire to hold it. Since it is not completely opaque, air bubbles are easily detected. The control mechanism is constructed from a standard hose clamp. Financial support for this project came from the National Research Council of Canads. CRAWFORD, C . M., J. C H E MEDUC., . 35,380 (1958). DuPont Bulletin No. A-6251.
Two pieces of No. 8 copper wire (3.3-mm diameter), A and B, are soldered to the jaws, as shown in the figure. To obtain good alignment it is advisable to solder one wire, A , to the stationary jaw, then tin the other jaw and one side of the other wire, B, and complete the soldering with the wire B clamped lightly in position. A toothed wheel, D, from an old alarm clock or toy construction set, is soldered to the knurled knob, C, to allow smooth control of the valve. Although the annealed tetrafluoroethylene tubing is sufficientlyrigid to support the weight of the clamp, it is advisable to provide additional support so that the valve may be operated with one hand. This may he accomplished with a small retort clamp or by soldering galvanized iron brackets, E and F, to the hose clamp as shown in the figure.
fW
d ? ! GMS. Top view
Volume
Side view
36, Number 3, March 1959
149
