Why are special bottles required for transformer oil sampling?

Special bottles minimize contamination, gas loss, and moisture ingress. For DGA, gas tight glass syringes or sealed bottles are used to prevent headspace and avoid gas exchange with air, which would distort results. For moisture and chemistry tests, clean dry containers prevent absorption of water and introduction of particles. Bottles may be pre cleaned and sealed, sometimes with septa caps for gas sampling. Proper containers and handling are critical because small sampling errors can lead to wrong maintenance decisions.