A small irony
HP and then Agilent were/are probably the largest manufacturer of gas chromatographs and mass spectrometers used to analyse sites for PCB and TCE contamination. PCBs were used mainly for dielectric fluids for large transformers and capacitors as well as plasticisers, flame retardants, coatings, etc., which might be where they came from.
One use for PCBs was as the pumping fluid for high vacuum diffusion pumps (as used in mass spectrometers). Some modern instruments still use diffusion pumps, but the fluids are normally silicone or polyphenyl ether oils - Although most of these systems now use turbo pumps,