Does the heat from the GCMS change the composition of the sample being tested?

Samples are introduced into the GCMS through a heated injector that volatilizes the components of the mixture. Any substance that is unstable at the temperature of the injector or the chromatographic column is likely to degrade. Those substances are known or are identified during method development and method validation studies and measures may be taken to mitigate or eliminate degradation during analysis.

In some methods (such as the GC determination of total THC), the acid form of THC is intentionally decarboxylated during GC analysis by raising the injector temperature to cause complete decarboxylation. On the other hand, the acids can be analyzed by GC methods if the acids are stabilized by converting them to derivatives before analysis. We routinely analyze acids of cannabinoids like CBDA or THCA by GCMS after derivatization without any evidence of decarboxylation.

A recent publication reported the results of an investigation of the degradation of cannabidiol to Delta-9-THC during GCMS analysis and identified several factors that contributed to this analytical problem. These factors included the type of glass used in te injector liner, the design of the liner, the temperature of the liner, the presence of packing materials in the injection liner, the temperature of injection, whether the injection volume was split or was splitless, the condition of the mass spectrometer detector (i.e., cleanliness), whether the sample was derivatized.