Tag Archives: flame ionization detector

Soapbox

Terpene Reconstitution: This Oak Barrel Is Not Your Answer

By Dr. Zacariah Hildenbrand
3 Comments

I’m not much of an oenophile but I recently came across a very interesting set of documentaries about sommeliers, which are experts on the science of wine and, most importantly, how wines are to be paired with food. What struck me as the most fascinating topic pertained to how mistakes made in the vineyard could be concealed by the barrel in which the wine is stored. For example, if the weather conditions throughout the season had been particularly tumultuous, and you end with sub-optimal grapes that are lacking complexity, then you can compensate for this by aging the wine in a variety of different oak barrels to enhance the flavor. To me, this is synonymous with the way that I’ve seen cannabis concentrates being handled, particularly with respect to terpenes. More specifically, it has recently become somewhat fashionable to supplement cannabis extracts with commercially available terpenes to reestablish an aroma profile that is most representative of the original stock material. Taken one step further, I have even heard of hemp extracts being supplemented with terpenes to achieve a particular strain phenotype, which I cannot imagine pans out very well. In my opinion, this is a very bad idea for two reasons:

One, cannabis is incredibly complex and can contain over 100 different terpene molecules, which can collectively act as anti-inflammatories (Chen et al., 2014), anti- microbial agents (Russo, 2011), sleep aids (Silva et al., 2007), bronchodilators (Falk et al., 1990), and even insulin regulators (Kim et al., 2014). So let’s say that you get your stock material tested and the laboratory screens the product for the top 25 most-prevalent terpenes: alpha- and beta-pinenes, linalool, limonene, beta-myrcene, etc. At that point you utilize this information to supplement your extraction product with these terpenes. However, you still may be missing information about other important molecules such as trans-2-pinanol, alpha-bisabolene and alloaromadendrene that are produced at extremely low, yet therapeutically relevant concentrations in the plant. So essentially with the limited information of the terpenes actually present in your stock material, you would be trying to rebuild a puzzle with only a small fraction of the pieces. Even Ben Affleck’s character in the movie ‘The Accountant’ can’t effectively pull this off.

An example of some commercially available terpenes on the market

Secondarily, not all commercially available terpenes are created equal. I’ll be the first to admit that I don’t have decades of experience vetting the quality of terpenes currently on the market; however, the several times that I have thrown samples into the GC-FID (Gas Chromatograph equipped with a Flame Ionization Detector) I have been unpleasantly surprised. Expecting beta-caryophyllene and detecting caryophyllene oxide is frustrating and in my opinion, such inaccuracies are wrong and should not be accepted as colloquialisms.

The moral of the story here is that in order to produce premium cannabis extracts/concentrates, the stock material needs to be handled with extreme care in order to retain the bouquet of terpenes in their natural ratios. This is incredibly important given the volatile nature of terpenes and their seemingly ephemeral, yet vital, nature in cannabis. Thankfully in this bourgeoning industry there are a number of extraction professionals who are delicately navigating the balance between art and science to produce premium products that are incredibly terpene-rich. However, for every alchemyst there is also someone trying to circumvent nature and while as a scientist I am inherently in favor of experimentation, I am also an admirer of natural processes.


Chris English
The Practical Chemist

Accurate Detection of Residual Solvents in Cannabis Concentrates

By Chris English
1 Comment
Chris English

Edibles and vape pens are rapidly becoming a sizable portion of the cannabis industry as various methods of consumption popularize beyond just smoking dried flower. These products are produced using cannabis concentrates, which come in the form of oils, waxes or shatter (figure 1). Once the cannabinoids and terpenes are removed from the plant material using solvents, the solvent is evaporated leaving behind the product. Extraction solvents are difficult to remove in the low percent range so the final product is tested to ensure leftover solvents are at safe levels. While carbon dioxide and butane are most commonly used, consumer concern over other more toxic residual solvents has led to regulation of acceptable limits. For instance, in Colorado the Department of Public Health and Environment (CDPHE) updated the state’s acceptable limits of residual solvents on January 1st, 2017.

Headspace Analysis

Figure 1: Shatter can be melted and dissolved in a high molecular weight solvent for headspace analysis (HS). Photo Courtesy of Cal-Green Solutions.

Since the most suitable solvents are volatile, these compounds are not amenable to HPLC methods and are best suited to gas chromatography (GC) using a thick stationary phase capable of adequate retention and resolution of butanes from other target compounds. Headspace (HS) is the most common analytical technique for efficiently removing the residual solvents from the complex cannabis extract matrix. Concentrates are weighed out into a headspace vial and are dissolved in a high molecular weight solvent such as dimethylformamide (DMF) or 1,3-dimethyl-3-imidazolidinone (DMI). The sealed headspace vial is heated until a stable equilibrium between the gas phase and the liquid phase occurs inside the vial. One milliliter of gas is transferred from the vial to the gas chromatograph for analysis. Another approach is full evaporation technique (FET), which involves a small amount of sample sealed in a headspace vial creating a single-phase gas system. More work is required to validate this technique as a quantitative method.

Gas Chromatographic Detectors

The flame ionization detector (FID) is selective because it only responds to materials that ionize in an air/hydrogen flame, however, this condition covers a broad range of compounds. When an organic compound enters the flame; the large increase in ions produced is measured as a positive signal. Since the response is proportional to the number of carbon atoms introduced into the flame, an FID is considered a quantitative counter of carbon atoms burned. There are a variety of advantages to using this detector such as, ease of use, stability, and the largest linear dynamic range of the commonly available GC detectors. The FID covers a calibration of nearly 5 orders of magnitude. FIDs are inexpensive to purchase and to operate. Maintenance is generally no more complex than changing jets and ensuring proper gas flows to the detector. Because of the stability of this detector internal standards are not required and sensitivity is adequate for meeting the acceptable reporting limits. However, FID is unable to confirm compounds and identification is only based on retention time. Early eluting analytes have a higher probability of interferences from matrix (Figure 2).

Figure 2: Resolution of early eluting compounds by headspace – flame ionization detection (HS-FID). Chromatogram Courtesy of Trace Analytics.

Mass Spectrometry (MS) provides unique spectral information for accurately identifying components eluting from the capillary column. As a compound exits the column it collides with high-energy electrons destabilizing the valence shell electrons of the analyte and it is broken into structurally significant charged fragments. These fragments are separated by their mass-to-charge ratios in the analyzer to produce a spectral pattern unique to the compound. To confirm the identity of the compound the spectral fingerprint is matched to a library of known spectra. Using the spectral patterns the appropriate masses for quantification can be chosen. Compounds with higher molecular weight fragments are easier to detect and identify for instance benzene (m/z 78), toluene (m/z 91) and the xylenes (m/z 106), whereas low mass fragments such as propane (m/z 29), methanol (m/z 31) and butane (m/z 43) are more difficult and may elute with matrix that matches these ions. Several disadvantages of mass spectrometers are the cost of equipment, cost to operate and complexity. In addition, these detectors are less stable and require an internal standard and have a limited dynamic range, which can lead to compound saturation.

Regardless of your method of detection, optimized HS and GC conditions are essential to properly resolve your target analytes and achieve the required detection limits. While MS may differentiate overlapping peaks the chances of interference of low molecular weight fragments necessitates resolution of target analytes chromatographically. FID requires excellent resolution for accurate identification and quantification.