Gas Chromatographic Determination of the Ethanol Content of Potable Liquids Using the Internal Standard Method

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Objective

In this experiment we would be ascertaining the percentage content of ethanol in 3 samples (spirit, wine and a beer). We would be comparing the concentration of ethanol to that of 25%propanol which would act as an internal standard.

Method

To set up the standards for a calibration curve we would make solutions of different concentrations of ethanol. Using a 25cm3 volumetric flask we would put 10cm3 of 25% Propanol into each one which would act as an internal standard. We would then add differing amounts of ethanol (0.5 cm3, 1.0cm3, 2.0cm3and 4.0cm3) and then top the volumetric flask up with distilled water. These would act as our standards to create a calibration curve. These standards are shown below in Table 1.0

Solution number| Volume of 25% propanol (cm3)| Volume of Ethanol(cm3)| Volume of H2O(cm3)| Percentage of Ethanol (%)| S1| 10| 0.5| 14.5| 2|
S2| 10| 1.0| 14.0| 4|
S3| 10| 2.0| 13.0| 8|
S4| 10| 4.0| 11.0| 16|
Table 1.0 Showing the percentage ethanol in the standard solutions

We would then make up solutions for our three samples. Predicting the possible percentage concentrations of ethanol we will make dilutions as necessary to fit within our region of confidence produced to our standards. Table 1.1 shows the solutions that were made up for the samples of spirit, wine and beer. It also shows the range of percentage values of ethanol we would expect in these samples.

Sample| Solution Number| Volume of 25% propanol (cm3)| Volume of Sample(cm3)| Volume of H2O(cm3)| Expected range of percentage of ethanol (%)| Spirit| S5| 10| 5| 10| 30-40|
Wine| S6| 10| 10| 5| 10-15|
Beer| S7| 10| 15| 0| 2-5|
Table 1.1 Showing the solutions made for analysis and the expected percentage of ethanol in each sample.

After creating the solutions we would run the solutions through the Gas Chromatography instrument. The Gas Chromatography instrument was a Focus GC and the experimental...
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