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Analysis by Gas Chromatography (SRI Model 420)


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Sample Chromatogram 

(500 ng/ul THC and 500 ng/ul CBD Lipomed standard)

Effect of decarboxylation on THC testing by Gas Chromatograph


A 20 gram sample of well-trimmed cannabis (Dakini Kush strain)  flowering tops was dried and sieved through a 20 mesh screen (20 openings per inch).   Mass loss due to evaporation was approximately 8%.  Four (150 milligram) samples were placed in separate crucibles.  One sample was kept at room temperature; while three samples were heated as follows:


Sample 1 - (Control Sample ) Not heated

Sample 2 - 230° F (110° C) for 110 minutes

Sample 3 -  250° F (121° C) for 27 minutes

Sample 4 - 300° F (149° C) for 7 minutes


Each sample was prepared for THC/CBD analysis by Gas Chromatography by combining 100 mg of  sieved plant material with 40 ml of denatured alcohol.  The alcohol contained 250 mg/l of methyl stearate as an internal standard.  The samples were analyzed and results are as follows:


Sample 1 - 0.4% THC

Sample 2 - 5.36% THC

Sample 3 - 16.49% THC

Sample 4 - 15.66%


Conclusion: Heating a sample for 250° F (121° C) for 27 minutes yielded the maximum THC result.


Two additional samples were prepared from the original 20 gram sample of Dakani Kush and heated to determine  the optimal time for decarboxylation:


Sample 5- 250° F (121° C) for 15 minutes

Sample 6 - 250° F (121° C) for 45 minutes


Samples 5 and 6 were prepared and analyzed as before.  


Sample 5 - 8.01% THC

Sample 6 - 15.98% THC


Conclusion: Heating a sample for 250° F (121° C) for 27 minutes yielded the maximum THC result.


Validation of Gas Chromatograph Results by High Performance Liquid Chromatography 


Samples of cannabis flowering tops were sieved and sample splits were submitted to MCR laboratories for analysis by High Performance Liquid Chromatography (HPLC).  The samples were also analyzed with the Model 420 Gas Chromatograph.  Results are shown below:

Conclusion: The SRIGC Model 420 Gas Chromatograph yields results similar to HPLC as long as the samples used for GC analysis are decarboxylated at 250° F (121° C) for 27 minutes prior to analysis.