Chemistry 439

Alcohol Content of Blood and Breath

I. Objectives:

II. Background:
It is illegal to perform various activities, including driving a motorized vehicle, if your blood alcohol level is above 0.08% ethanol by volume. The density of ethanol at room (20 C) temperature is about 0.7893 g/ml so a concentration of 0.08% by volume is approximately 0.063% ethanol by weight.
During 2001, the warden of the prison in Vienna, IL was driving with a friend home from a meeting. They had an accident and the friend was killed. The warden was taken to a Kentucky hospital where his blood alcohol level was measured to be 0.082 % by volume. Another sample was taken later and measured in Illinois as 0.046%. The warden was charged with manslaughter. Using one of the procedures below, do you think you could measure the difference between 0.079 % (legal and innocent) and 0.082% (illegal and guilty) of ethanol in blood?

III. Procedure:
Obtain an aqueous unknown containing ethanol from your TA. You are to measure the percent of ethanol, on a percent by volume basis, in the sample and report both the percent and the 95% confidence limits for your determination. You will then convert your results to a percent by weight and report that number.
Prepare a series of calibration standards by adding a known volume of absolute (pure) ethanol to enough water to provide a known volume of solution. The most frequently used concentration for the stock solution is 1.00%. Since the legal limit of ethanol in blood in most states is 0.08% by volume, the working calibration standards should be well below and above that number. Again, a convenient way to prepare the calibration standards is to dilute the 1% stock solution to concentrations from 0.05% to 0.20% ethanol in a water solution. You are to prepare a calibration curve of peak area (instrument units) vs ethanol concentration using a GC to obtain the ethanol peak areas. The instrument should be equipped with a capillary column specifically designed to separate low molecular weight alcohols. However, alcohols are hard to separate on gas chromatograph columns so you should expect some peak tailing. You should also be aware that you will be working close to the method detection limit so your best analytical technique will be required. The procedures for operating the different instruments are inside the instrument log book.
Choose the settings for the injector, oven and detector based on your knowledge of GC and the boiling point of ethanol (78.4 degrees C).
After making 10-15 injections, heat the detector to 275 C and the column to 250 C to clean the column and then return to the settings above for subsequent analyses. Heat the column as the last thing you do on the instrument so the next group will have a clean column to start their analyses.

Report
Report the equation for the calibration curve (Y = mX + b) where mg etoh/ml of solution is the Y coordinate and the peak area is the X coordinate. The numerical value of the slope and intercept will be graded so be sure your units are as specified. Determine the amount of error in your measurements and