A Versatile and Inexpensive Ebullator for Sample Concentration %"I%" Samples for GLC or HPLC often need to be concentrated, or the solvents need t o be removed and replaced. For examples, TMS carbohydrates are often prepared l,lPl in pyridine. If chromatographed as such, small amounts of low-molecular-weight I I,-1 materials are obscured by the solvent front. Consequently, it is a common practice to remove the pyridine by evaporation and replace it with hexane or chloroform. Nitrogen is bubbled through the sample to facilitate evaporation. The ebullator herein described is a modification of one reported by Berozal et al in 1972. The changes incorporated in this new design, i.e., a syringe needle and W*iLd a GLC septum, permit greater flexibility in the number of samples treated (1 to 20). The device is constructed of inexpensive and readily available laboratory equipment. The manifold is constructed from a l/s in. to '14 in. brass reducing union. Alternatively, the main body of the manifold can be constructed from other types of fitting, e.g., a reducing tube fitting or a plastic connector. AV-in. GLC septum is placed aver the %in. end of the reducing union and secured in place by a nut. This unit will serve as the manifold. A disposable needle, from which the Luer fitting has been removed, is inserted on each end of a piece of Tygon (Teflon or polyethylene) tubing. One end pierces theseptum and the other end is placed under the surface of the sample t o be concentrated. Gas flow is controlled by a needle valve. Disposable needles are readily available in a number of sizes. The needle shaft is easily separated from the Luer fitting by scoring with a triangular file and then bending back and forth. This procedure prevents crimping of the end. The combinations of a 22G X 1% in. needle with 0.025 in. LD. Tygon tubing worked out well. The septum did ndt leak even after several needle insertions and removals. A number of other needle-tubing combinations are possible. However, needles thicker than 22G leave a permanent hole in the septum. This option is useful since changes in bubbling rate can occur following the addition or removal of needles from the manifold. This effect can be minimized by utilizing a needle tubing combination with a smaller I.D. Once the student removes his sample and needle from the septum, the flow of nitrogen automatically stops even if he forgets to turn off the cylinder valve.
Beroza, M., Bowman, M. C., and Bierl, B.,Anol. Chem., 44,2411 (1972). The mention of firm names or trade products does not imply that they are endorsed by the US. Department of Agriculture over other firms or similar products not mentioned National Regional Research Center Agricultural Research Science and Education Administration US. Department of AgricultureZ Peoria, IL 61604
J o h n Lehrfeld
Volume 57, Number 8, August 1980 / 587
