A Constant Flow Device for lon-Exchange Columns In performing ion-exchange column chromatography, it is frequently desirable to have a constant flow rate. In certain studies, this requirement is mandatory. Gravity flow, where feasible, is the easiest and most economical method of achieving a constant flow rate, but requires some sort of a constant head device. A very simple device has been suggested recently by Rieman and Walton.' In the student laboratory, and in many research applications, columns are frequently prepared in a buret, or similar tube. The diameter of these columns, being on the order of 1-2 cm, makes the insertion of the two glass tubes fmm the above device difficult. We have built devices based on Rieman and Walton's design for use with buret columns, and have found that a constant level could not-be maintained to any better tolerance than about 4cm. The problem was overcome by the simple alteration, shown in the figure, of making the tubes concentric. The outer tube was made from 10-mm tubing, the inner tube from 3-mm tubing. A U-bend was made in the inner tube which allowed it to hook over the edge of the outer tube as shown, and kept it from falling out of the flask. The length of the outer tube, fixing the depth to which it protrudes into the column, defines the level which will be maintained. The entire device can be fabricated in just afew minutes time. Our experience with this device has been extremely favorable. The difference in diameter of the two tubes allows air bubbles to pass between them readily. Constant levels have been maintained to a tolerance of 0.5 cm in routine work m t h no special precautions. An added advantage offered by such a device is the freeing of the operator from making frequent additions of eluent. The pmtuding tuhing lends enough stability that the assembly can be rested atop the buret without additional support. In such cases, a small gmove must be made in the top oi the stopper which rests an the buret, to allow air to pass and prevent a seal from forming. 'Rieman, W., and Walton. H. F., "Ion Exchange in Analytical Chemistry," Perpamon Press, Oxford, England. 1970, p. 136. Patrick G. McConnick M q u e t t e university Milwaukee, Wisconsin 53233
Volume 51, Number 1, January 1974
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