How is PCB content tested in transformer oil?

PCB content is tested by collecting a clean oil sample and analyzing it in a certified laboratory using chromatographic methods, most commonly gas chromatography with appropriate detectors. The result is reported in ppm or mg/kg and compared to regulatory thresholds that determine handling, labeling, transport, and disposal requirements. Screening test kits may exist for field indication, but compliance decisions usually rely on lab results and chain of custody.