While watching the local news, you’ve probably heard of people in your area getting arrested for driving under the influence. Across the U.S., driving with a blood alcohol concentration (BAC) (link to chart on CDC website) greater than or equal to 0.08 percent is a crime, with penalties varying by state (link to drunk driving laws by state chart). There is some variation in legal limits in different countries around the world (link to world map with BAC limits).
BAC is usually measured as mass per volume. For example, a BAC of 0.03% means there are 0.03 grams of alcohol in 100 grams of a person’s blood. Headspace gas chromatography (link to GC page) coupled with a flame ionization detector (link to product page) is one of the most common methods for measuring BAC in forensic labs. This method allows a large number of samples to be analyzed quickly and precisely. Ethanol is the main substance tested for during analysis, but scientists can also look for methanol, acetone, and 2-propanol.
Accuracy is crucial in blood-alcohol analysis, since legal decisions can be made based on a person’s BAC at the time an accident or incident occurs. However, blood is a complex matrix that can have a lot of variation from person to person, for example in the salt or lipid content. So how do forensic scientists and toxicologists make sure their test results are reliable?
Flame Ionization Detector Sensitivity
The typical instrument configuration for analyzing BAC via headspace gas chromatography with flame ionization detection consists of a static headspace instrument for sample introduction, followed by gas chromatography (GC) with two capillary columns for separation, and two flame ionization detectors (FIDs) for detection and quantitation.
Flame ionization detectors are mass sensitive, meaning their measurements are proportional to the mass of the carbon that passes through them. FIDs operate by detecting ions formed during the combustion of organic compounds in a hydrogen flame. The generation of these ions is proportional to the concentration of organic species in the sample gas stream. Hydrocarbons generally have molecular response factors equal to the number of carbon atoms in their molecule. Molecules that contain only carbon and hydrogen respond best to flame ionization detection. As ethanol (link to chemical fact page) is primarily made up of hydrogen and carbon, it can be accurately analyzed by FID.
Tools for Blood Alcohol Content Analysis
There are multiple state-of-the-art tools available for analyzing a large volume of BAC samples quickly and precisely. Gas chromatography systems (link to product page) work well thanks to their versatility, with features like instant-connect modularity. Modules can be installed by the user in less than two minutes, with no special training, dedicated tools or on-site service engineers required. Such modules include the Instant Connect Flame Ionization Detector (link to product page) and the Instant Connect Split Splitless Injector (link to product page). Another gas chromatography-mass spectrometry (link to product page) system is designed to ensure reliable performance in all ionization modes. Source components are composed of solid, inert material, including a repeller that assists in maintaining instrument performance over time.
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- Rapid, Automated, and Accurate Determination of Volatiles in Human Blood by Headspace Gas Chromatography (application note)
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