The Chemistry of Cannabis

Detection in the Body

Well everyone, this is our sad farewell. This is going to be the last blog post on The Chemistry of Cannabis. For our final topic, we’re going to discuss how Cannabis is detected in the body. For this post, we’re going to focus on one of the more common methods of Cannabis detection in the body: hair testing. Additionally, we’re going to focus on one of the more standard methods of analyzing hair: gas chromatography/mass spectrometry. We know that sounds like a lot of big words and a pretty confusing thing, but don’t worry, its not as bad as you think. Now, we don’t want to spoil too much in the intro, so we’re going to move right into the topic.

Hair Analysis

Before we go into hair analysis, let’s talk a little bit about why this method is used. First, it is non-invasive. Second, it is cheaper than most other methods of Cannabis detection. Finally, Cannabis can still be detected in hair months after consumption, while other methods cannot be reliably performed after several days. This has to do with the nature of how Cannabis gets into the hair. During the growth phase, every strand of hair is connected to the body’s circulatory system. Consequently, the metabolites, or products of metabolism, ofCannabis are deposited in the hair through the bloodstream, and become the chemical that reveals prior use ofCannabis. As the hair grows, the section in which the Cannabis metabolites reside is pushed up, and the deposit contents remain unchanged. A diagram of human hair containing chemical substances is shown to the right. Theoretically, one can test deposits from years ago, although most tests only go as far back as 90 days. Going more in depth, there are multiple ways of actually detecting certain Cannabis metabolites in hair.

 Gas Chromatography/Mass Spectrometry

Before this process begins, the hair shafts first need to be decontaminated. Hair shafts are washed with methanol (CH4O), the structure of which is seen to the left, to remove external contamination. This compound is used because it dissolves any contaminants that are present while leaving the hair intact. Methanol is not corrosive, and so it will not break down the hair. Additionally, it has a polar and a non-polar end. Remember the saying “like dissolves like”? It is the general rule for solubility; molecules tend to dissolve other molecules that have the same polarity. Because of this concept, polar and nonpolar contaminants are attracted to the methanol and virtually all potential contaminants can be washed away. After decontamination is complete, the hair matrix is broken down. Sodium hydroxide is commonly used because it is highly basic and thus corrosive. Compounds are released from the hair matrix, and can now be analyzed for specific drug metabolites.

Next, the two-step analysis begins. The first step is gas chromatography (GC). Chromatography is often used to separate colored dye into individual components. The same idea applies here: the chemicals in a hair strand are separated and, if present, Cannabis can be detected. One microliter of the mixture containing the compounds is injected into the sample column. Then, the sample column is heated to a temperature above the boiling point of all the compounds. The vapor is carried by an inert, or chemically inactive, gas through the coiled column, which is cooler than the sample column. The coil is packed with diatomaceous earth, or very porous rock, which is then coated with a liquid with a high boiling point. The basic setup for this process is shown in a diagram to the right.

Now, this is where this really gets interesting. Some compounds have very strong intermolecular forces, or interactions between the same molecules, so these compounds “want” to be closely packed in the solid state, and thus have a high boiling point. These compounds will condense on the diatomaceous earth. However, some of the compound will sublimate again into the gas phase until an equilibrium is established. Because the molecules are constantly condensing and subliming, the molecules with strongest intermolecular forces take the longest to move through the column with the inert gas.

Other compounds will dissolve in the liquid. Their polarity affects their solubility in the compound, and so molecules with the same polarity as the liquid will spend less time in the gas phase and take some time to move with the inert gas (although less time than those that completely condense out). The molecules that travel with the inert gas the fastest are those that remain in the gas stage the longest. These compounds have weak intermolecular forces which cause low boiling points, and so the cooler temperature of the chamber is warm enough to keep them in the gas stage.

As you can see, the differing characteristics of molecules affect the speed at which they travel through the column, so they are separated based on these characteristics. As each one reaches the end of the column, they are fed into a mass spectrometer. Mass spectrometry enables precise identification and quantification of each distinct component. In a mass spectrometer, the separated compounds are first ionized by knocking away an electron, resulting in a net positive charge. Then, the compounds are set into motion and deflected with either an electric or a magnetic field (the molecule needs to be charged to be able to be deflected by one of these fields). The degree of reflection is dependent on the mass of the compound; heavier molecules are deflected at a smaller angle than lighter molecules are. Some simple illustrations of how this process looks are shown in the image below. Mathematical analysis is done to relate the degree of reflection to the mass, and violà, you have the mass of the compound, which serves to identify the constituent elements. If a suspected molecule has the same mass and moves through the column at the same speed as a standard sample of a Cannabis metabolite would, then the presence of Cannabis in the bloodstream has been verified.

Now, of course, gas chromatography used with mass spectrometry isn’t the be-all, end-all to hair analysis. There are various other methods used to analyze hair, and new ones are constantly being researched and developed. Additionally, hair analysis isn’t the only method used to detect Cannabisin the body. Cannabis can be detected in many different parts of the body, including in blood, saliva, and urine. The various methods and the techniques used to employ them are where we leave you, and hopefully we’ve been able to teach you a little bit about one of the most effective and common methods.


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