In the Laboratory
A Simple Streaking Device for Preparative Thin-Layer Chromatography Yong J. Kim Department of Chemistry, Sun Moon University, Galsanri 100, Tangjeongmien, Asansi, Chungnam, Korea
Preparative thin-layer chromatography is a routine practice in many organic synthesis laboratories. A capillary tube or disposable pipet is usually used for loading a sample on a preparative TLC plate. The problem of using a capillary tube is that it holds only a small amount of sample at a time. With a disposable pipet sample flow is difficult to control.
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There is a commercial streaking device (Kontes Glass Company) for preparative TLC that is convenient but expensive. If the right tool is not available, loading a sample on a TLC plate is fairly tedious and time consuming. Here I describe a procedure for making a simple and convenient streaking device from a Pasteur pipet (illustrated in the figure). First, draw a capillary from the narrower part of a pipet and seal the end while pulling it apart using the flame of a microburner (a). Second, close the other end (the thicker end) of the pipet with a finger and flame one area of the pipet for a while. A small hole will be made at this spot by the expanding air inside the pipet (b). The hole should be fire-polished in the flame. Third, bend three places in the pipet as shown (c). Hold the pipet in the flame several seconds; it will be bent down naturally. The hole in the pipet should be placed at the top. Last, cut off the sealed tip of the pipet at a proper length. The finished device should look like (c). A sample solution can be loaded in the device through the hole (d). Capillary action draws the fluid out of the device. The device can be dragged on a TLC plate to make a streak or can be used as a normal capillary tube to make sequential spots.
Journal of Chemical Education • Vol. 75 No. 5 May 1998 • JChemEd.chem.wisc.edu
