Blood Alcohol Concentration by Headspace GC-FID
Over the end of year holidays I’ve been known to have an alcoholic beverage or two in the evening when I have nothing else to do. This got me thinking about BAC and what it takes to test that.
I know that a field breathalyzer can use either IR Spectroscopy or Potassium dichromate for the detection of alcohol in the breath, but what about detection of alcohol in the blood? This is where the GC-FID comes into use, but not just any GC, but headspace GC.
Headspace GC is where the sample is placed in an air tight sample vial and then, often times, heated to release any volatile compounds into the gas phase. That gas phase is extracted with a gas tight syringe and injected in the GC.
For this experiment I have several different standards ranging from 10 mg/dL to 100mg/dL which corresponds to 0.01% to 0.1%. Normally, blood would be drawn from someone suspected to be driving under the influence of alcohol, but we aren’t equipped to handle biohazards, so I will be using synthetic blood for my samples. The samples were made by adding a known amount of ethanol to the synthetic blood.
The standards and results were analyzed using the following method.
| Lucidity GC-FID Conditions | |||
|---|---|---|---|
| Carrier | Hydrogen | ||
| Control | Pressure | ||
| Flow | 1.0 mL/min | ||
| Column | RTX-WAX | 30 m x 0.25 mm, 0.25 um | |
| Injector | 125 ℃ | ||
| FID | 250 ℃ | ||
| Oven Program | |||
| Rate | Temperature | Hold Time | |
| 40 ℃ | 4 min | ||
| Headspace Program | |||
| Incubation Temperature | 70 ℃ | ||
| Incubation Time | 7 min | ||
| Syringe Temperature | 80 ℃ | ||
Chromatogram of the 0.08% Ethanol standard
Once the standards have been run, a calibration curve is established for the method.
Ethanol Calibration Curve run on a Wax column
The samples were prepared using synthetic blood ordered from VWR. Each of the samples was randomly made by a second lab chemist. The only guidelines they were given was to have the amount of ethanol be less than 1 mL and the total sample size be 1.5 mL. Set out with this task they got the samples made, and I tested them using the headspace autosampler and the GC-FID.
Chromatogram of sample 1 showing a BAC of 0.093% from the calibration curve
Sample 1 has a result of 0.093% BAC, the sample was prepared using 169 μL of 0.80% ethanol in 1500 mL total, giving a BAC calculated of 0.090%.
Chromatogram of a sample 2 showing a BAC of 0.197%
Sample 2 was prepared using 375 μL of the 0.8% ethanol solution into the synthetic blood, giving a BAC of 0.20%. The chromatogram shows a BAC of 0.20%.
These two runs demonstrate a pretty successful measurement of BAC vs actual BAC (0.090% versus 0.093% for Sample 1 and 0.20% versus 0.20% for Sample 2).