Retention time stability in a gas chromatographic apparatus

Apparatus for performing a chromatographic analysis of a fluid in a separation column having an outlet subject to a barometric pressure p.sub.atm, comprising:

• fluid flow controller for providing a selectable flow of the fluid in the separation column;
• a plurality of transducers for sensing a respective plurality of actual operating condition parameters to which the fluid flow is subjected, the plurality including the barometric pressure p.sub.atm ;
• means for providing information representative of a desired operating condition parameter;
• a processor for:
• a. determining a desired average linear velocity of the fluid flow according to the desired operating system parameter,
• b. determining an actual average linear velocity of the fluid flow according to the sensed plurality of actual operating condition parameters;
• c. determining, 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;
• and
• an interface for providing a control signal representative of the determined fluid flow amount to the fluid flow controller.