In the Laboratory edited by
Harold H. Harris University of Missouri-St. Louis St. Louis, MO 63121
Flash Chromatography: A Novel Pressurization Apparatus Jeffrey D. Butler,* Wonken Choung, and Mark J. Kurth Department of Chemistry, University of California, Davis, Davis, California, 95616 *
[email protected] Since its introduction by Still et al., flash chromatography has become a mainstay technique for the purification of organic mixtures (1). Improvements have been made to this basic technique to make it safer by implementing a lateral reservoir (2), simpler through apparatus modification (4), and a better instructional tool by reducing the time required for the separation of a model system (3). Flash chromatography implies that the column is pressurized to increase the flow rate. Usually the column is pressurized using a “house” system of compressed air that typically delivers a pressure that is too high for proper flash chromatography (5). Importantly, novel methods to pressurize the column continue to be explored to address the safety issues that arise when pressurizing glass columns (6). Further, the absorbent silica gel bed used for separations has a tendency to crack when sudden pressure changes occur, a common difficultly in teaching laboratories (7, 8). To address several of these flash chromatography issues, we have developed a modified setup allowing the column to be pressurized using a common blood pressure bulb and valve system. Our system consists of a 90° ground-glass adaptor (24/40 adaptor, Chemglass, CG-1014), a convenient length of
Tygon tubing, and the pressure source, a Baumanometer latex bulb and Air-Flo control valve. The bulb and control valve assembly can be purchased through several retailers for $10-$15. Connecting one end of the tubing to the bulb and control valve and the other end to the 90° ground-glass adaptor completes the assembly. This assembly can be inserted into the column and clamped in place (Figure 1). The complete assembly is considerably less expensive than the pressure control valves sold by column manufactures for $60-$80. A rubber stopper with a hole to accommodate the tubing can be substituted when using columns without ground-glass joints. Because the bulb valve assembly is not capable of generating a highly pressurized system, the primary benefit of the setup is the reduced risk of overpressurization. That said, the setup easily provides ample pressure to pack the column using either the dry or slurry methods addressing issues identified by Jacobson (9) and Krause (10). The Air-Flo control valve allows the pressure in the column to be released gradually protecting the silica gel bed from cracks. The system requires two or three compressions of the bulb periodically (every couple of minutes depending on the column size) to maintain a properly pressurized column. Because the users' hands are free, the method allows for the TLC of fractions as they are eluted so that target compound(s) can be identified the moment they elute, saving time and reducing solvent waste. Further, the method can be used in laboratories not equipped with compressed air and provides a necessary water-saving alternative to widely used aspirator methods. This method has been in use in our research laboratory for 4 years and has proven to be reliable and broadly applicable across a wide range of solvent systems and column sizes. As such, it provides a useful and inexpensive alternative for both teaching and research laboratories. Literature Cited
Figure 1. Flash chromatography employing the pressurization assembly.
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1. Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923– 2925. 2. Ponten, F.; Ellervik, U. J. Chem. Educ. 2001, 78, 363. 3. Bell, W. L.; Edmondson, R. D. J. Chem. Educ. 1986, 63, 361. 4. Thompson, W. J.; Hanson, B. A. J. Chem. Educ. 1984, 61, 645. 5. Deal, S. T. J. Chem. Educ. 1992, 69, 939. 6. Horowitz, G. J. Chem. Educ. 2000, 77, 263–264. 7. Feigenbaum, A. J. Chem. Educ. 1984, 61, 649. 8. Shusterman, A. J.; McDougal, P. G.; Glasfeld, A. J. Chem. Educ. 1997, 74, 1222–1223. 9. Jacobson, B. M. J. Chem. Educ. 1988, 65, 459. 10. Krause, J. G. J. Chem. Educ. 1991, 68, 790.
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r 2010 American Chemical Society and Division of Chemical Education, Inc. pubs.acs.org/jchemeduc Vol. 87 No. 11 November 2010 10.1021/ed100416x Published on Web 09/09/2010
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Journal of Chemical Education
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