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Chemistry LibreTexts

Alcohol

Analysis of a Simulated Blood Sample for Ethanol

Objective

To determine the concentration of ethanol in a blood sample; to see if the person being tested was legally drunk.

Sample

A simulated blood plasma with added ethanol. Store the aqueous solution in a tightly closed vial in the refrigerator; the solution is stable for at least one month.

Preparation of Simulated Blood Plasma

Draw a small amount of yellow food coloring into a Pasteur pipette and squirt it out again. Rinse the pipette with deionized water and dilute the rinsings to about 10 mL. Add a few drops of this colored solution to the volumetric flask, in which the analyte sample is being prepared, to approximate the pale yellow color of blood plasma.

Reagents

Ethanol (analyte), n-propanol (internal standard)

Standard Reference Material

The standard reference material is simulated blood plasma with a concentration of 0.10% (w/v) ethanol. Store the aqueous solution in a tightly closed vial in the refrigerator; the solution is stable for at least one month.

Method

Gas chromatography; direct aqueous injection

Special Equipment

Capillary gas chromatograph with thick-film Carbowax column (e.g. 30 m x 0.25 mm x 0.5 µm) and flame ionization detector

Procedure

For instructor (detailed); For student (brief)

Typical Results

Chromatogram: 1 µL injection of liquid sample at 1:40 split; isothermal separation at 70 degrees C; 1 mL/min helium flow; elution order is (1) ethanol (2) propanol

Calibration curve: (peak area ethanol / peak area propanol) vs. concentration of ethanol