The ability to measure the amount of alcohol in a blood sample is fundamental to determining if a person violated the law. DUI laws usually prohibit exceeding a certain amount of alcohol in a person system. This task requires that a laboratory develop a measurement system.
Within that measurement system is a machine called a gas chromatograph. The machine performs two primary tasks: (1) it separates the substances within a sample; and then (2) measures how much of each substance is present.
The machine doesn’t inherently know how to identify any specific substance. It must be taught. This process is known as calibration. This is accomplished using calibrators. A calibrator is known and specific amount of alcohol. Here, the term means the concentration of alcohol (i.e. 00.08) in water.
Each time the machine tests a group of subject samples several calibrators are placed in the machine. These calibrators teach the machine specific alcohol concentrations. This calibration process essentially builds a virtual ruler out of the different concentrations.
However, what happens if the calibrator isn’t what you tell the machine it is? That is, you tell the machine that a calibrator is 00.08, but it’s actually a lower concentration. Before answering that question, consider the stability of an ethanol calibrator.
Evaporation is the process of changing a liquid into a gas. Different substances have different rates of evaporation. Ever use hand sanitizer? Your hands dry faster with an alcohol based sanitizer than when you wash them with water. This is because a gram of alcohol evaporates significantly faster compared to a gram of water.
The evaporation process of alcohol starts when it’s exposed to air. Open your 00.08 calibrator, expose it to air and evaporation begins. If you leave it exposed to air long enough, before using it, then enough evaporation will occur to materially reduce the concentration. Degradation can happen after only a few minutes.
With this in mind, what happens when a degraded calibrator is used to teach a machine an alcohol concentration? The machine is taught incorrectly. You have told the machine (entering a value into its software interface) that this calibrator is 00.08 when in reality the concentration is significantly less. Not only has the calibrator degraded but now the machine’s virtual ruler has also been degraded.
Take a look at the above video and it will illustrate what happens when a degraded calibrator is used. You will see that a test result for a subject sample is artificially inflated. Put another way, the test result might incorrectly show a result above a legal limit. And the machine provides no indication the result is wrong. All because the machine had a bad teacher.
