I have moved this post to an application area and updated the tags for better visibility .
PCBs are not commonly sampled via headspace. SPE is more commonly used as a cleanup step followed by standard auto-sampler injection. PCBs are more often detected using MS or uECD due to their more selective operation. I've attached some separation conditions to get you started, but they don't provide headspace or FID conditions.
This note discusses some improvements in sample cleanup: https://www.agilent.com/cs/library/applications/5990-9164EN.pdf
Dissolved gases in insulating fluids are analyzed using headspace - GC/TCD/FID, and guidance for that analysis is located in ASTM D3612C. That configuration implements gas sampling and switching valves to optimally separate the gases.
I hope this information is helpful. Please respond with additional questions and I'll do my best to assist.