Dear Sir. Concerning your issue about how to formulate the pathway of degradation from the result of gcms. Every stage of the flow path in GC can degrade your results, from the inlet liner to the ion source. To solve this, Here are five tips for GC flow path inertness, so you can be confident that nothing has been added to or lost from your sample, even when components are present at trace levels. Maintain the inlet Preventive maintenance which helps to ensure the best instrument performance and productivity. Prevent sample loss at injection Inlet liners are critical links in the sample flow path. Using glass wool in liners can trap non- volatiles and extend column lifetime. Use a column with low activity Active sites within columns that are not optimally deactivated can negatively affect peak shape and peak response. Highly inert columns minimise compound loss and degradation, and provide more accurate quantitation of active analytes, especially at trace levels. Remember your detector, if you have used inert liners and column, but still have issues with breakdown products, then active sites in your detector could be responsible. To ensure accurate quantification and high sensitivity, the entire flow path must be highly inert, including detector surfaces. Purify your gases Contaminants in gases can significantly affect your analysis. Moisture, oxygen, and hydrocarbons contribute to loss of sensitivity and undermine the accuracy of the GC. For more detailed,  the following below attached file may help you in your analysis:

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The only significant way to demonstrate that a transformation product (TP) derive from a specific parent compound is the use of labelled parent compound. But this is expensive and unpractical, becuase there are few commercially available labelled compounds. So the most of the degradation pathways are inductive and founded on the knowledge of the chemical reactivity