the microscale laboratory
perature, precipitated by the addition of distilled water, and isolated by vacuum filtration. The recovered mass of N-tert-butylbenzamide is 437 mg for a yield of 51%N-tertbutylbenzamide: mp = 131-133.5 "C; literature mp = 133135 "C (12). IR (CHC13,cm-') 3420,3050,1645,1505,1210. Literature Cited 1. Williamson, K. L. Mocmscole and Micrmmk Orgvnie Ezpriments; D.C. HeaUI: Lexington, MA, 1989; pp 171-180. 2. Mayo, D.W.: Plke, R. M.; BuWler, S. S.Micmsmlr Orgonichbordory; John Wlley: NewYork, 1986:pp 112-117. 3. Lehman, J.OpmliomiOganieChemislry;AllynandBamn: Boston, 1998;pp 1 6 s 177~ ~~
4. Rodig, 0. R.; Bell, C. E.: C1ark.A. K O w n i c Chemistry hbomtory: Saunders College Publishing:Phibdelphia, 1990; pp 203-209. 5. Kildah1,N.;Berka,L. H. J Cham.Educ. 1993,70,671. 6. Erwin,D. K. J Chem Educ. 1991,68,862. 7. Rieci, R. W.: Ditzler, M. A. J Chem. Educ. 1991,68.228. 8. f i m e n . L. I.: Cota. 0. J. OmanicRocfions 1969.17212425. . 9. Mvndy, B. ~ l k ; d .M. 0 . " Rpocfions ~ ~ and ~ Remen& in Oganie Chemistry; John Wiley: NewYork. 1988: n, 18CL181. 10. Mareh,J.Aduancd Oganie Chemistry. 4hed.; John W~ley:NelvYork,pp97G971. 11. Chtisto1.H.: Lsurmt.A.:Mouaseron.M.BuN. Soc. Chim. X). 1961.2313-2318.
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PI
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2. Landgrebe, J A . Thooryondhctice in IheOganieLnbomfory,4th ed.:BraaksiCole: Pacific Gmve, CA: 1993: p 31. 8. Williamson. K.L. Mocrosmle and Micmseda Org.nie Ezmn'mnts:DC Heah: Lerington, MA; 1989; p 15.
Manual Head Space Sampling for Gas Chromatographic Analysis Jeffrey A. Corltill and Kenneth W. Raymond Eastern Washington University Cheney, WA 99004 Gas chromatography (GC) is one of the most frequently used techniaues for the analvsis of volatile ~roductsderived from microscale organic chemistry experiments (18). Manual iniection of liauid samples is the most irre~roducible facecof GC anal& espekally for novice chromatorwil~hers. - . The usual method of iniectine a 1-2 JL liouid sample can frequently result in inappropriate injection volumes (either too large, resulting in massive solvent peaks that can obscure &ly anal& peaks, or too small, resulting in unreliable chromatograms). In addition, inadequate syringe cleaning can lead to inter-sample contamination. These factors can seriously affect the reproducibility and the accuracy of GC analyses. We have found that a manual head space sampling technique can alleviate or reduce most of the aforementioned problems of solvent injection. This head space method is particularly well-suited for use in microscale experiments where, frequently, only limited amounts of products are available. The syringe handling techniques of such head space sampling are much easier and present much less of an obstacle to obtaining meaningful chromatographic data for students. Tvoicallv. students lace one d m (40-100 ~ uL) of their mixmixt'ure f& analysis in a 1dram viai, seal the latter with a Teflon-lined caD and dace the vial.in an 60-80 OC oven for about 45-90 %'ThecLp i s removed and the needle of a syrinec (we use a 10-uL SGE rcolaceahln needle s e n g e with a gexible plungerj is positioned in the centerbf tLe vial. The oluneer is pumped twice and 3 5 uL of head mace vap& is &-awn ;ntoLthe syringe. The k p l e is inje'cted ra~idlvinto the GC iniector. The figure shows an example of; student chromato&am obtain; using this techniq;e. In our organic chemistry laboratory, manual head space sampling for GC has increased si@~cantly both the productivity of sample processing and the reliability of the quantitative analysis of mixtures of volatile organic compounds.
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A Simple But Accurate Pipet for Use in Microscale Organic Labs Gerald C. Swanson Department of Science Dayiona Beach Community College 1200 International Speedway Blvd. Dayiona Beach, FL 32114 Calibrated pipets can he made by students for use in dispensing small amounts of liquids in microscale organic chemistry experiments (13).These consist of disposable Pasteur pipets, which students calibrate during their first lab period. The calibration is usually limited to 0.5- and 1.0-mL volumes. The accuracy of the pipets is dependent on the quality of the student's calibration techniques. An inaccurately calibrated pipet results in incorrect volumes of liquids being dispensed throughout many of the subsequent experiments. Additionally, the tips of the pipets sometimes brake off, requiring the preparation of new calibrated pipets during later experiments. A simple and more accurate pipet can be constructed from l-mL serological pipets. Since an ordinary pipet bulb will not fit on this size pipet, an adapter can be made from a Pasteur pipet and a short piece of rubber tubing, as shown in the figure. Once made, this adapter can become part of the normal equipment stocked in the lab drawer. Literature Cited 1. Pauis, DL.; Lampman, G.M.; M z , G.S.; Engel. R.G.Inlmducfion faOrg.nieLnbomlow Technioues.A MiemseoleAoomoch. 3rd d.: Saunders:New Yark: 1990: o 44
Literature Cited
Adaptation of the serological pipet for microscale use A202
Journal of Chemical Education
1. Pavia. D. L.: Lampman, G. M.: M l , G. S.:Engel, R. G. Inkduction to OrganieLobom t w y TPchniwes. A Mtcmscok Appmoch. 3rd ed.; Saundera College Publishing: Philadelphia. PA, 1992: Experiments 8, 11, 14, 16, 18. 2. McRitFhiclkkly D.: Gab"elsm, B. Ogonie Chemistry in the Lnbomfory, 2nd ed.; KendalWunt: Dubuque. lA, 1985:Experimenta l6snd 28. 3. Maya, D. W.; Pike, R. M.; Butcher, S. S. MicrweleOganieLabwolory,2nd ed.:John Wtley: New York, 1989: Experiments 1.5.9. . C. Heath and CN Lexington, 4. Williamson, K. L.Miemsmla Oganie Ezprimnfs: D MA. 1987: Expetimenfs 11-13. 5. Peterson, T H.; Blyan, J. H.; Koevil. T A J. Chem Educ. 198% 70.A96.498. 6. Wigal, C . T;Hopkins, W T;Ronald, B. P. J Chem. Edue 1631,68,A229. 7. Lee. M. J C k m . Educ 1992.69.Al72A173. 8. Gmch, E. E. J. Chem Educ ISSO, 67.A232-A233.
the microscale laboratory
Atotal Ion chromatogram JS ng head space sarnpllng oota~nedby a st~dentfrom a sample aenveo from tne acla catalyzed oehydrauon reamon of cyclohexylrnethanol Tne xy ene was ~ s e dn the synlhesls both to Increase tne en~cencv of tne o st1 allon of the alnenes out of the orlo nal reaction mixture and as a retention times reference. Asmall amount of unreacted alcohol is evident.
Volume 71 Number 8 August 1994
A203
