The main diffusion processes that are in devices for testing of transformer oil for gas chromatography are considered. The estimation of time for safety storage of most movable gas in transformer oil - hydrogen in several types of syringe, is shown. It is obtained that the most suitable device is "Elchrom", where used both glass frame of syringe and glass plunger. Besides it has PTFE sealing gasket that lead to the safety of the gas in probing during more than one month. The equilibration time for gas in oil and gas in gas phase is estimated for some devices of gas extraction.