In the Laboratory edited by
Cost-Effective Teacher
Harold H. Harris University of Missouri—St. Louis St. Louis, MO 63121
An Inexpensive, Disposable Cannula Filtration Device Brian K. Bennett and Thomas G. Richmond* Department of Chemistry, University of Utah, Salt Lake City, UT 84112-0850
Although several techniques have been developed for the filtration of air-sensitive solutions (1), these procedures utilize expensive and elaborate apparatus that require tedious drying and cleaning protocols (2). These systems are both cost- and time-prohibitive for the undergraduate student laboratory. We wish to report a very simple and inexpensive filter constructed from filter paper, septum, and a Pasteur pipet. Solutions are delivered by cannula with positive nitrogen pressure allowing for filtration with facile exclusion of water and air. The apparatus is constructed in minutes and is simple enough to be used routinely in advanced undergraduate synthetic laboratories.
Pressure Release
Rubber Septum For 5 mm NMR Tubes
Syringe Needle Or Short Cannula Copper Wire Tie
Cannula
Applied N2 Gas Positive Pressure
Qualitative Filter Paper
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Filtered Solution
Heterogeneous Solution
A 2-mL Pasteur pipet is cut to yield a short length of glass tube (ca. 3.2 cm). On one end of the tube an NMR septum (5 mm) is fitted and wired; on the other end a small disk of qualitative filter paper (3.0-cm diam) is wired (see illustration). The excess filter paper is then trimmed away with scissors. The end of a cannula is fed through the septum as far as possible without puncturing the filter paper. A second, larger, septum is fitted on the cannula male side towards the filter, which is fitted, with N2 purge, on the flask containing the heterogeneous mixture. The solution is forced through the filter and cannula to the receiving flask by positive pressure, where a small disposable syringe needle allows for the release of pressure. The chief advantages are that the filter requires no special drying procedure and is conveniently disposable. Very small particulate matter can be separated and both air-sensitive solids and mother liquor can be isolated simultaneously in micro to macro amounts. Literature Cited 1. Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-Sensitive Compounds, 2nd ed.; Wiley: New York, 1986; pp 15, 22, 192. Wayda, A. L.; Darensbourg, M. Y. Experimental Organometallic Chemistry: A Practicum in Synthesis and Characterization; American Chemical Society: Washington, DC, 1987; pp 6, 12–14. 2. Urbancic, M. A. J. Chem. Educ. 1988, 65, 65. Sintered glass filters require cleaning with strong oxidizing agents such as concentrated HNO3 , K2Cr2 O7 /H 2SO2 , or H2O2 /H2 SO4 and extended drying times at elevated temperatures.
*Corresponding author.
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Journal of Chemical Education • Vol. 75 No. 8 August 1998 • JChemEd.chem.wisc.edu
