Gas v. Liquid Chromatography

Gas v. Liquid Chromatography

Gas chromatography and liquid chromatography differ in one way that is important to the analysis of cannabinoidsGas chromatography uses heat and liquid chromatography does not.  Heat allows the sample of marijuana to go through a chemical process called decarboxylation, which is a necessary step to determine the exact amount of CBD and THC that can be absorbed into the body.  The body will not absorb marijuana that has not been decarboxylated, which is why prior to a patients use marijuana is always exposed to heat.  Marijuana is decarboxylated either through smoking, vaporizing, or cooking butter. Link

Analyzing medical marijuana without decarboxylation, like through liquid chromatography, allows only for the measurement of the maximum THC and CBD possible in a sample.  This produces high numbers that are not useful to patients because they will need to decarboxylze marijuana in order to feel its effects.

This is why Gas Chromatography has been the method of choice for the quantification of cannabinoids by both the United Nations Office on Drugs and Crime (UNODC) and the National Institute on Drug Abuse (NIDA).

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NIDA Peer Reviewed Method:

GC–MS Analysis of the Total 9-THC Content of Both Drug- and Fiber-Type Cannabis Seeds

Authors: Ross S.A.1; Mehmedic Z.2; Murphy T.P.3; ElSohly M.A.4

Source: Journal of Analytical Toxicology, Volume 24, Number 8, November/December 2000 , pp. 715-717(3)

Publisher: Preston Publications


A GC–MS method was performed to determine the total 9-THC content in both drug– and fiber-type cannabis seeds. Drug-type seeds were found to contain much higher levels of 9-THC (35.6–124 g/g) than fiber (hemp) seeds (0–12 g/g). The majority of 9-THC was found to be located on the surface of the seeds. Approximately 90% of the total 9-THC was removed by a simple, quick wash with chloroform. Washed drug-type seeds contained less than 10 g/g. Separation of the seeds into the kernel and testa showed that the bulk of 9-THC is located in the testa, mainly on the outside. The kernels of drug- and fiber-type cannabis seeds contained less than 2 and 0.5 g 9-THC/g seeds, respectively. Fluctuations in the 9-THC content of different replicates of the same type of seeds could be the result of the degree of contamination on the outside of the seeds.

Language: English

Document Type:

Affiliations: 1: National Center for Natural Products Research, Research Institute of Pharmaceutical Sciences, School of Pharmacy, University of Mississippi, University, MS 38677 and Departments of Pharmacognosy, School of Pharmacy, University of Mississippi, Uni 2: National Center for Natural Products Research, Research Institute of Pharmaceutical Sciences, School of Pharmacy, University of Mississippi, University, MS 38677 3: ElSohly Laboratories, Incorporated (ELI), 5 Industrial Park Drive, Oxford, MS 38655 4: National Center for Natural Products Research, Research Institute of Pharmaceutical Sciences, School of Pharmacy, University of Mississippi, University, MS 38677 and Department of Pharmaceutics, School of Pharmacy, University of Mississippi, Univ

Publication date: 2000-11-01

UNODC Peer Reviewed Method:

UN methods for THC testing

1. Introduction
1.1 Background

Cannabis products are the most widely trafficked drugs worldwide, accounting for 65 per cent of all global seizure cases (1.65 million cases) in 2006. 5,200 metric tons of herb and 1,000 metric tons of resin were seized in 2006. Practically all countries in the world are affected by cannabis trafficking. Similarly, cannabis also remains the most widely used drug worldwide, with an estimated 166 million people having used cannabis in 2006, equivalent to some 4 percent of the global population aged 15-64.

At the same time, especially since the end of the last century, production methods have become increasingly sophisticated, resulting in the availability in illicit markets of a wide range of cannabis products with widely varying levels of the main psychoactive ingredient, delta-9-tetrahydrocannabinol (THC). Most recently, there has lso been a renewed debate about increasing THC content (frequently referred to as “potency”) in illicit cannabis products. All of this requires analytical data which are comparable between laboratories and over time.

However, most countries do not require by law the detailed analysis of the THC content of the different products, and where such analyses are carried out, they use a variety of approaches and experimental designs, reducing the comparability of results. For example, the conversion of natural constituents, such as tetrahydrocannabinolic acid (THCA), by both smoking and under certain analytical conditions into THC, and how this should be reflected in the analytical report, are issues which are not yet standardized worldwide.

On the technological side, the analysis of cannabis products is further complicated by the relatively restricted availability of pure or well defined reference material of THC and other cannabinoids.* The present manual is an updated and significantly revised version of the manual on “Recommended methods for testing cannabis” (ST/NAR/8), which was published in 1987. It has been prepared taking into account both developments in analytical technology and advances in the science of cannabis, and with a view to providing the analytical basis for an objective discussion about changes in THC content over time, and differences between regions and products.

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