Nonsteady-state flow in gas chromatography during fast changes in inlet pressure

The steady-state assumption for describing the flow in a capillary gas chromatography column fails when changes in inlet pressure are introduced at a fast rate. To accommodate the possibility of nonsteady-state conditions, or a transient behavior, a second-order nonlinear differential equation for the pressure is suggested. Good agreement between the new theoretical model and representative experimental results is shown when the inlet pressure is increased at a rate of several hundred kPa per minute; in contrast, predictions from traditional steady-state calculations are relatively poor.