Patent ID: 8343258

Claim:
A device for providing a constant mass flow rate to a downstream column system of a gas chromatograph, the device comprising: a small full scale mass flow controller configured to control a carrier gas to flow at a first mass flow rate; a flow resistance element having a finite flow resistance, the flow resistance element comprising an inlet port connected to a sample inlet, an outlet port connected to the downstream column system, and a pressure sensing port in fluid communication with both the outlet port and the small full scale mass flow controller for receiving the carrier gas at the first mass flow rate; a sample inlet pressure controller configured to control the sample inlet at a first pressure; and a pressure sensor configured to measure a second pressure of the carrier gas at the pressure sensing port of the flow resistance element, wherein a set point of the first pressure is determined as a function of the second pressure, the flow resistance of the flow resistance element, and a second mass flow rate from the inlet port to the outlet port of the flow resistance element, and the mass flow rate to the downstream column system is kept constant by controlling the first pressure to equal the first pressure set point.