Retention time stability in a gas chromatographic apparatus

摘要

The effect of barometric pressure variation on the retention time stability of a chromatographic analytical system is compensated by active control of the amount of fluid flow by way of a fluid flow controller, preferably in the form of an electronic pressure control system. Control signals are derived by: receiving data representative of a desired operating condition parameter, such as column inlet pressure; sensing actual operating condition parameters such as inlet pressure pi and barometric pressure patm; determining a desired average linear velocity of the fluid flow according to the desired operating system parameter; determining an actual average linear velocity of the fluid flow according to the sensed plurality of actual operating condition parameters; and controlling, as a function of a predetermined relationship of the desired average linear velocity to the actual average linear velocity, the amount of fluid flow to cause the actual average linear velocity to substantially equal the desired average linear velocity.