Marijuana Math: Figuring Potency by Fill Weight

Figuring potency based in a complicated formula for something like an infused topical or edible can be daunting. Often there are several different ingredients with different densities that make the calculations difficult and confusing. There’s a much easier way: Fill Weight.

The Fill Weight is the actual weight of the product. For topicals that would be the weight of the product in the container. For a cookie that would be the weight of a single cookie.

To find the weight in a container simply weigh the container empty, fill it with a known amount of product, and weigh it again. Subtract the weight of the empty container from the weight of the filled container and you have the fill weight. Pretty simple, huh? As long as you put the same weight of product in each container, your potency should be the same each item.

Here’s an example:

An empty 60ml jar weighs 5 grams. The total weight of a filled 60ml jar is 45 grams. Subtract 5 from 45 to get the fill weight: 40 grams. That means the weight of the product inside the jar is 40 grams.

Let’s say the product tested at 2.0% CBD.
First, convert grams to milligrams. 40 grams = 40,000mg
Multiply milligrams by percentage. 40,000 X 2.0% = 800
There’s 800mg of CBD in the 60ml (40g) jar of product.

Here’s another example:

A cookie weighs 4 grams and tests at 0.15% CBD
4 grams = 4,000mg
4000 X 0.15% = 6
The whole cookie has 6mg of CBD.

So how much does your product weigh?

That’s not always an easy answer, at least not if you’re in the United States. Unlike most of the world, the U.S. uses the imperial system of weights and measures rather than the metric system. Where this gets in the way (or weigh) is when an ounce isn’t really an ounce.

The imperial system uses “ounce” to indicate both weight and volume. But a one-ounce jar of lead doesn’t weigh the same as a one-ounce jar of water, and ten ounces of feathers will take up more space (volume) than ten ounces of water, so you have to know what you’re talking about.

The weight of a tincture in a one-ounce bottle will vary depending on its formula. This gets particularly complicated when it comes to topicals where ingredients are often whipped together with air taking up space without adding weight.

We work in the metric system, and if you’re producing a cannabis product, you should too. It’s so much easier to keep weight and volume straight during formulation when you’re talking milligrams and milliliters.

If you need to convert ounces to milligrams, there are some great calculators online that make it easy.

Get a good scale

The real trick is having an accurate metric scale that measures in milligrams (.001 gram). The accuracy of your scale can really skew your results. If you want us to figure your Fill Weight, simply send an empty jar along with the full jar to be tested and we’ll weigh, compare and make the calculations for you.

Now you know how to figure potency by Fill Weight. Pretty simple and pretty useful.

Go forth and formulate good products. And remember to get them tested at The Good Lab.

Potency testing: GC vs. LC

Alex-Edwards-at-LP-Analytical-3At The Good Lab, we use High-performance liquid chromatography (HPLC) for potency testing. Why is that important? Here’s a great explanation of the difference between gas chromatography (GC) and liquid chromatography (LC) from Lift Cannabis News Magazine (Canada).

Potency Testing

Marijuana is a complex matrix. Like many natural products it contains thousands of compounds, many of which have yet to be discovered or understood. Separating out the THC and CBD from the diverse soup of compounds contained in your marijuana is essentially like looking for a few needles in a big haystack.

Chromatography is the chemist’s way of sorting out that haystack. In the cannabis world, potency is tested by liquid chromatography or gas chromatography. Although there are some promising techniques for testing potency using spectroscopy instead of chromatography, chromatography is currently the industry standard method used in Cannabis testing labs from Colorado to Uruguay.

How it works

To get an understanding of how chromatography works and what the “liquid” and “gas” terminologies mean, one first needs to look at the “column”. This is where the separation occurs in both liquid and gas chromatography.

A column is basically a tube that contains a chemical phase or material (the stationary phase) and a “mobile phase” which is what keeps everything moving through the column (this is where the “liquid” and “gas” part comes in). In gas chromatography the mobile phase is a gas (an inert gas like helium, hydrogen or nitrogen) and in liquid chromatography the mobile phase is a liquid (like methanol, acetonitrile and water).

For the separation to take place, the marijuana extract gets put onto the column, and will be transitioned through the column from one end to the other by the mobile phase. The components inside the extract (the THC and CBD) will have varying affinity to stay in the stationary phase that lines the column. Some will stay in longer than others, so they become separated from each other.

gc vs lc liftcannabis caAt the end of the column, once each of the components have been separated, they will be detected or “counted”. There are differences between the way the THC and CBD are detected between liquid or gas chromatography. In gas chromatography (GC) you often see that the analysis is called “GCFID”. The FID part stands for “flame ionization detector” which is essentially like it sounds – a flame! The FID will burn the compounds as they exit the column and an electrical signal is measured. This signal is directly proportional to the amount of the compound present.

In this type of liquid chromatography, the measurement is by UV (ultraviolet). A light in the wavelength range of the ultraviolet (yes, the same UV that your Oakley sunglasses are blocking from your eyes) is directed through the compound as it exits the column. The helpful characteristic of the THC and CBD molecules is that they absorb UV light, and this absorption can be measured and is directly proportional to the amount of the compound present.

You may have noticed that “LC” is often referred to “HPLC”. This was just the chemists adding more letters to something that was already concise and sensible. The “HP” stands for high pressure, or sometimes “high performance”, which varies from manufacturer to manufacturer. Some even call their systems UHPLC or ULTRA high pressure liquid chromatography. A higher pressure system will do the analysis faster, but that’s it.

So what about the other cannabinoids? Chances are, if you are reading this blog you are aware that there are a lot of other important cannabinoids in marijuana; CBN (cannabinol), CBG (cannabigerol), CBC (cannabichromene), delta-8-THC and many, many more! Why are these not reported? Especially as there is an indication that these compounds have important medical properties. Well, for now, it is not required. But many labs and licensed producers are already testing for these other cannabinoids. And what about the acid forms of the compounds, THC-acid and CBD-acid? This brings out an important discussion that relates directly back to the analysis by GC versus LC.

The effect of the main psychoactive compound (THC) is greatly reduced unless the THC-A is converted to THC. When cannabis is heated, the acid forms of the cannabinoids will readily convert to their neutral forms. Without heating (and not waiting for a long time) THC will remain in acid form, and this structure of the molecule doesn’t bind to the receptors in our brain that happily accept the neutral THC (THC with the acid removed).

Why does this affect the choice of analytical instrumentation? Well, in order for GC (gas chromatography) to work, the marijuana extract has to be converted to gas form, which means it is heated before entering the column. Any acid cannabinoid compounds, such as THC-A will be converted to their neutral forms, and no acid compounds will be detected, Conversely, in LC, the extract in liquid state can be injected onto the column as is, and therefore, you can quantify all the acid and neutral forms of your cannabinoids.

Some argue that the GC better mimics the state in which marijuana is typically consumed; by smoking or vaporizing. However, many patients may choose to vaporize at lower temperatures, and they may in fact be consuming some of the cannabinoids in acid form. And what about the potential medical benefits of the acid cannabinoids and the other unreported cannabinoids such as CBC? At this early phase in our industry, we at Signoto believe it’s better to provide as much information as possible to medical practitioners and patients. It’s time to move quickly away from the mystery era of cannabis.

~Emily Kirkham

VP of Laboratory Operations at Signoto.

Thank you Lift Cannabis News Magazine for allowing us to share this! Please visit their site for more information on all things cannabis in Canada.

Go out and start your own lab

We fought hard to get access to the licensed cannabis labs for patients and caregivers, but the industry and the Marijuana Enforcement Division is having none of it. They told us if you want testing for patients, go out and start your own lab.

So we did!

Frustrated with the lack of testing available to home cultivators, especially patients who need information about their medicine, we decided to do something about it. Thanks to the support of one of the state licensed labs, we can provide quality, accurate test results you can rely on.

We starting out by offering a Cannabinoid Potency Profile using High Performance Liquid Chromatography (HPLC). We’ll be expanding our services over the next several months.

For more information or to make an appointment:
Call 303-455-3801