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Background Information: Commercial mouthwashes are mixtures of water, alcohol, dyes, flavorings, and other compounds. In this experiment, you will use gas chromatography to determine the alcohol content of the mouthwash. Since the volumes of alcohol and water are not additive when mixed, a calibration curve must be used. It will provide the correction factor needed for alcohol-water mixtures. The calibration curve will be prepared by placing a known amount of alcohol in an alcohol-water mixture. The observed percentage of alcohol will be plotted against the true percentage of alcohol.

Equipment/Materials: 95% ethanol distilled water gas chromatograph (w/10 PL syringe) mouthwash samples Procedure: 1. Warm-up and set-up the GO as directed. Use a chart speed of 2 CM/min. Set the attenuation to 4 or 8. Inject 0. 5 PL of 95% ethanol to determine the best attenuation to use. All of the other alcohol peaks will be smaller than this one, so the 95% peak should be as high as possible. 2. Prepare standard solutions of ethanol according to the following amounts. 1% volume alcohol 195% alcohol (ml/100 ml) 1 120% | 5. 26 121. 05 1 110% 1 130% 110. 53 131. 58 3. Obtain 1. PL off standard solution and add about 5 PL of air.

Inject the sample into the GO. Label the standard injected and attenuation. Follow the same procedure for each standard solution. 4. Obtain 1. 0 PL off mouthwash sample and about 5 PL of air. Label the mouthwash injected and attenuation. Follow the same procedure for each mouthwash sample. Rinse the syringe with toluene between injections. Data Analysis: 1. Determine the retention time of the 95% alcohol. 2. Use the retention time to identify the alcohol peaks of the standard solutions and mouthwash samples. 3. Determine the area under each alcohol peak by measuring he height of the peak and the width at h the height.

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