E.
s.
Hanmhan
Marshall University Huntington, West Virginia
I
Xylene Analysis
II
Integrated experiment in, instrumental analysis
T h e series of experiments described here, has been designed with two primary objectives. First, using the same unknown sample in several experiments provides continuity and stimulates student interest. Second, the use of an unknown which contains major "impurities" encourages individual initiative and provides the student with a realistic problem of the type he will undoubtedly encounter in independent work. The unknown used is a "Technical" grade xylene, which contains major amounts of ethylbenzene and toluene in addition to the three xylene isomers. The first experiment in this series is an infrared analysis similar to that described by Ewing (I). Alert students will note the presence of major components in addition to the xylenes. Consulting the literature references provided (2-6)aids in identification of these components, and the student is allowed to continue the experiment to attempt to develop full identification if he desires to do so. I n all experiments, no detailed instructions for reporting results are given, and the student is graded on the originality of his report as well as on completeness and accuracy. Gas chromatographic analysis is a natural supplement to the infrared analysis. The experiment is based on the work of Mortimer and Gent (6), and uses a twelve foot column of "Bentone-34"-di-isodecylphthalate (10%) on "Chromosorb P." Results of the analysis of a synthetic mixture prepared from chromatoquality xylenes are shown in Table 1. The experiment is carried out using an F & M Model 500, operated isothermally a t 8@120°. The student is provided with pertinent literature references (6, 7) which, if consulted, aid in the identification of toluene and ethylbenzene as the major impurities. This information can then be used to reinterpret the results of the infrared analysis. Table 1. GLC Xylene Analysis Component
Observed
Calculated
The instrnctions provided do not require the identification of the two major impurities, but chromatoquality samples of both toluene and ethylbenzene are kept available. Presented in part before the Southeast-Southwest Joint Regional Meeting of the American Chemical Society in Memphis, Tenn., December, 1965.
Table 2 shows the results of student analyses of the same xylene sample used previously in the infrared experiment. Also shown is the "theoretical" composition, obtained by Rossini, et al. (a),by analysis of cooling curves. This corresponds to the theoretical composition of petroleum xylenes calculated from thermodynamic properties. Table 2.
GLC Xylene Analysis
Component
Found
Theoretical=
Ortho Meta Para Ethylbenzene Toluene
19.5 42.5 17.0 16.0 5.0
21 48 19 12
= Rossini ( 8 ) .
This experiment can easily be extended in scope to investigate programmed temperature operation and effect of carrier gas flow rate and temperature on theoretical plate number. The third phase of the xylene analysis experiment is carried out as a supplementary experiment. I n a preliminary ultraviolet experiment, the student uses the Beclcman Model DB to obtain spectra of benzene and the xylene isomers in cyclohexane or iso-octane. I n addition, the spectrum of benzene vapor is obtained using the "Narrow" and "Medium" slit programs of the DB, and also using the minimum slit attainable by manual adjustment. The bare minimum of directions are provided, and the student is asked to evaluate and comment on his results, and to evaluate ultraviolet spectroscopy as a potential tool for xylene analysis. I n the second, supplementary, phase of this experiment, the student is again supplied with pertinent literature references (9-11) and asked to carry out the analysis of an unknown containing either xylenes, xylene plus ethylbenzene, or xylenes, ethylbenzene and toluene, using the results of the preliminary experiment to determine the feasibility of analysis of these mixtures. Preliminary results indicate that a precision of 5% is a b tainable in the analysis of the ternary mixture. At the end of the semester, one class period may be used to discuss the results of these experiments, emphasizing the accuracy, precision, and usefulness of each technique. Student response has been generally favorable. A continuing problem of this type tends to generate more interest than experiments which are treated as completely separate and unrelated problems. I n addition, the use of the technical grade sample as an unknown alerts the students to the danger of forming premature opinions about the results of an experiment. The case for this approach is stated clearly by Hamhlen (19), " . . our classroom experiences are not close
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Volume 43, Number 6, June 1966 / 321
enough to the real world. The classroom treats the ideal case. Problems in the texts always have soluin world that is tions. , , our graduates quite different."
.
Literature Cited (1) EWING,G. W., "Instrumental Methods of Chemical Analy-
sis," 2nd Edition, McGraw-Hill Book Company Inc., New York, 1960, p. 409. (2) KAYE,W. I.,AND OTIS, M. V., Anal. C h a . , 20, 1 ~ 1 6 , (1948).
D. M., (3) FRANKEL,
AND
JOHNSON, C. E., Anal. Chem., 30,
550, (1958). (4) SCHNURMANX, R., AND KENDRICU,E., Anal. Chem., 26, 1263, (1954).
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Journal o f Chemical Education
(5) YOUNG,C. W., DUVALL,R. B., AND WRIGHT,N., Anal. Chem., 23, 709, (1951). (6) "oRT1"W J. AND GENT,P. L., Anal. Chem., 36, 754, (1964).
(7) ZLATKIS, A., LING,S., AND KAUFMAX, H. R., Anal. Chem., 31, 945, (1959). (8) ROSSINI,F. D., AND STREIFF,A. J., National Bureau of Standards, R P 1830. (9) WHITE,R. G., in "Progress in Infrared Spectroscopy," Vd.
I. (Editor:SYZMANSKI, H. A.) Plenum Press, New York, 1962, p. 297. D. D., BRATTAIN, R. R., AND ZUMWALT, L. R., (10) TUNNICLIFF, Anal. Chem., 21, 380, (1949). R. T., A N D STEARN, A. E., Anal. Chem., 21, 1361, (11) VAUGHN, (1949). (12) HAMRLEN, J. W., Science, 150, 965, (1965).
