A sample pump system for metering the amount of sample taken from a pressurized fluid process such as a natural gas pipeline or the like, the sample pump system designed for immersion, directly or indirectly, into the pressurized fluid stream so that the sampling is taken at the prevailing pressure and temperature of the fluid stream. A spot sample cylinder device is further provided which employs a method of collection wherein the initial cylinder volume of the collection vessel or sampling cylinder is zero. The spot sample cylinder is inserted into the pressurized gas (or fluid) source, said sample cylinder employing a piston or moveable end configured such that purging of the cylinder sample cavity is not required, since the sample cavity volume is essentially eliminated prior to sampling by the location of the piston within the cavity, the cavity expanding upon sampling via piston movement within the cavity.