This article from Issue 16 of the Analytix Reporter demonstrates how the reusable Carbotrap® T420 tube allows monitoring and determination of terpenes in variety of settings including cultivation environments and high humidity conditions.
INTRODUCTION
There is a growing interest in sampling terpenes from the air. Since gas chromatography is the most common technique used for terpene analysis, a new thermal desorption (TD) tube specific for sampling terpenes relevant to cannabis and hemp was developed. This provides a means to monitor/determine terpene concentrations in the cultivation environment.
Thermal desorption is less wasteful and more environmentally friendly than single-use devices since the TD tubes can be reused and no (toxic) solvents are required for the sample preparation workflow. TD is capable of sampling a wide range of terpene concentrations by either adjusting the sample volume (how much air pulled through the tube during sampling) or by adjusting the split flow ratio of the thermal desorber prior to the analysis to transfer more or less of the sample to the GC instrument and detector.
Air sampling near live plants or dried plant materials provides a simple way to determine the concentration of the different terpenes released by the plant at a given time and under specific growing or drying conditions. With thermal desorption, only the volatile compounds, such as the terpenes are collected by the TD tubes. Less volatile compounds, such as tetrahydrocannabinol (THC), and cannabinoids, are not released into the air by the plant due to their much higher boiling points. So, for analysis only the TD tubes are sent to the laboratory, not any plant material. The technique is non-invasive/less destructive.
Knowing the terpene concentration emitted from the dried plant material could provide valuable information to growers and dispensaries, since the terpene odor can influence customer purchasing decisions.
What is Thermal Desorption?
See the full article for a brief introduction to this sample preparation technique for GC.
EXPERIMENTAL CONDITIONS
To quantify the terpene concentration, a thermal desorption tube must be able to retain the terpenes during sampling, but it also must efficiently release them during the desorption step. During the research, it was discovered that no single adsorbent could provide good recoveries for all the terpenes relevant to cannabis and hemp samples. Therefore, a new multi-bed TD tube was set out to be developed that was named the Carbotrap® T420. It contains two different graphitized carbon black adsorbents that offer different surface areas and retentivity (weak and medium), resulting in excellent recoveries of the target terpenes. To demonstrate the performance of this new Carbotrap® T420 tube, it was tested alongside a TD tube packed with Tenax® TA, which is a commonly used adsorbent in the field of thermal desorption.
Analytical Conditions
For the conditions and instrument parameters for the analysis of the collected samples on the TD tubes, please refer to the full article.
Calibration
We combined two multi-component terpene test mixes and then added neat β-myrcene to the final mix to create a comprehensive terpene test mix for calibration and to challenge the TD tubes. See Table 1 (in full article) for the specific details.
RESULTS & DISCUSSION
Recovery Experiments
To test the recovery, each of the TD tubes was spiked with 0.5 µL of the terpene test mix and challenged with 2 and 10 liters of nitrogen gas. To spike the TD tube the Adsorbent Tube Injector System (ATIS) was used. It is a sample preparation device designed to transfer calibration standards or test mixes onto a TD tube. The recoveries on the Carbotrap® T420 tube were similar or better compared to the Tenax® TA tube.
Uptake of Moisture During Air Sampling
Additionally the water uptake was investigated showing that the Carbotrap T420, due to its hydrophobicity, is suitable for sampling also under humid conditions.
For full details of the results and discussion, please refer to the article.
Conclusion
The Carbotrap® T420 thermal desorption tube has been specifically designed for sampling terpenes in air. It exhibits excellent recoveries of terpenes relevant to the cannabis and hemp industry for sample volumes of up to 10 liters of air. This new adsorbent tube is also suitable for sampling in humid atmospheres, such as greenhouses as it does not retain water.
Thermal desorption can be considered as an eco- friendly sample collection and analysis technique since the used tubes, such as the Carbotrap® T420, can be re- conditioned and reused multiple times. Furthermore no (hazardous) solvents are required in the desorption process, that would need to be sourced and later disposed after the analysis.
The Carbotrap® T420 is available as both glass and stainless-steel tubes. Glass tubes do have the advantage of allowing a visual observation of the integrity of the adsorbent packing with repeated use and are generally considered to be more inert. Stainless-steel tubes are more durable and will not break when sampling under harsher conditions in the field. Each TD tube contains a unique barcode for easy sample identification and tracking. The tubes are designed to function with any thermal desorption instrument that accepts ¼ in. O.D. x 3.5 in. long tubes (6.35 mm O.D. x 89 mm length).
*The life science business of Merck operates as MilliporeSigma in the U.S. and Canada.