Mark Yuan Harvey Mudd College Claremont, California 9171 1
The gas chromatograph is one of the most useful and common analytical twls in the undergraduate lahoratory. 114 great utility and popularity warrant a firm understanding hy the student of the theory and practice of gas chromatography. Too often, because of time limkations, the student cannot discover for himself the effects of varying some of the parameters in gas chromatography such as column temperature or different liquid phases. Often retention times are too long for the student to make more than a few runs in a lab period and the columns must he changed in order to see the effect of different liouid nhases. A computer program has been written in interactive FORTRAN IV to model a eas chromatomaph and to output a chromatogram-like traceon a ~ e k t r o n i xgraphics termkal or a Calcomn The user selects a liquid phase, a sample . . . nlotter. . mixture, a column temperature, and a n output attenuator setting. Each simulation takes about two minutes to run, from the selection of the column to the complete output of the chromatomam. The prigram makes use of the facts that chromatographic oeaks are often Gaussian in form and that the log ot therekntion volume is p r o p d o n a l to the reciprwal ofthe absolute temperature over a limited temperature range.' L'sing chromatographic data gathered in the lahoratory and plotting retention volume versus reciprocal absolute temperature on semi-logarithmic paper, the slope for each unknown sample on each liquid phase over a varying temperature range was
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A Gas Chromatographic Simulation Program determined. When the user specifies a sample mixture, a column choice, and a column &mperature, he specifies the retention volume. At this retention volume, a Gaussian peak is output. The height and width of this peak are determined hv the sample choice and liquid phase and are calculated within the program. This program does not take into account leading or tailing peaks. Examples of output obtained from the graphics terminal are shown in the accompanying figures. Fiaure lo shows the trace wlth the liquid phase being DC-710 with the column temperature a t 60°C. Figures l b and l c show the trace with the same liquid phase hut with column temperatures of 80 and 10O0C,respectively. Changing the liquid phase and holding everything else constant can have a dramatic chromatoeram. Firmre 2a shows the trace ~ ~effect ~ ~- on ~ the -~ ~ ~ ~ with the liquid phase beingdiisode&l phthalate with the column temnerature a t 60°C. Firmres 2b and 2c show the trace with the same liquid phase hut with column temperatures of 80 and 100°C, respectively. The program was designed to aid the student in discovering what effects certain parameters, e.e., column temperature, designed to r&ce the have on the chromato~ram;it was vnluahle "hands-on" time that the student has with a real chromatograph. With a better understanding of what effect the changing of basic parameters can have on the chromatogram, the student will he able to make better use of both his and the instrument's time. Copies of the program, documentation, and sample output are available upon request. ~
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' Purnell, Howard, "Gas Chromatography,"John Wiley and Sons, New York, 1962, p. 214.
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Figure 1. Simulated chromatogram of a sample midure of hexane, benzene, cyciohexane, cyclohexene, n t i a 1:24:8, on a DC-710 column. (a) Temperature at 60°C. (b) Temperature at 80%. (c) Temperature at 100°C.
364 1 Journal of Chemical Education
Figure 2. Simulated chromatagram of a sample mixture of hexane, benzene. cyclohsxane, and cyclohexene, ratio 1:2:4:8. on a diirodecyl p h h l a t e column. (a) Temperature at 60% (b) Temperature at 80°C. (c) Temperature at 100°C.
