The Determination of Alcohol Content of Beer: A General and Analytical Experiment with High Student Interest Value This experiment was undoubtedly the mast papular in our advanced general chemistry course this year. It introduces gas chromatography, one of our most powerful research and analytical tools, and demonstrates several useful analytical techniques while providing results which are definitely "relevant" to the average college stpdent. Apparatus: Separation was done on a Carle "Basic" model 650OT gas chromatograph using the standard ?Q in. X 5-ft dinonyl phthalate column and a Heathkit model EUWdOA recorder. Reagents: Absolute ethanol, USP Reagent quality, U S . Industrial Chemicals; 1-propanol, Baker analyzed reagent, J.T. Baker Co.; Helium carrier gas. Procedure: A standard curve is made with 3.0-10.0 vol% solutions of ethanol in water which are then "spiked" by the addition of 10.00 ml prapanol per 100.0 ml of standard solution. One microliter of each final solution is injected into the gas chromatogra&(with 8 0 ' ~ column temperature), and a working curve is made by plotting the ratio of peak heights of ethanol to propanol versus percentage ethanol in the original standard solution. Samples of beer are then spiked with 10.00 ml propanol per 100.0 ml of beer and chromatographed as above. The ratio of peak height ethanol to propanol is used to determine the percent ethanol directly from the standard curve. We performed the experiment during two 3-hr laboratory periods for a general chemistry course, but it could he done in one session for a quantitative analysis class. The first session was used for discussion and demonstration of gas chromatography followed by eaeh student, or pair of students, making up standard solutions and determining one point an the standard curve. The standard point results were exchanged and each made his awn working curve. For the second laboratory period eaeh brought in whatever beverage he wanted to test. A few points of the standard curve were rechecked and the remainder of the period was spent analyzing the samplesand comparingresults. This experiment is useful as an introduction to analytical techniques for general chemistry and is also well suited to an analytical chemistry course. The careful solution preparation, the method of standard additions and the preparationand usage of a standard curve are all valuable techniques. The author wishes to thank Dr. P. B. Reiehardt for helpful suggestions. University of Alaska Fairbanks, 99701
D. A. Lokken
Volume 52, Number 5. May 1975
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