In order to allow verification of the purity of a fluid sample from a pressurized fluid system, a sampling assembly includes a pressure chamber adapted to removably receive a sampling container. An inlet in the pressure chamber of the sampling assembly is connected to a bleed point of the pressurized fluid system of which the fluid is to be sampled, and the fluid in the system is caused to flow for a predetermined time interval through the sampling container in the pressure chamber. An outlet of the sampling assembly is connected to a return point of the fluid system. When the sampling assembly is disconnected from the fluid system, the pressure in the pressure chamber is released and the sampling container now containing a representative sample of the fluid in the system may be removed from the sampling assembly for analysis of its contents.