Simple correction for variable post column split ratios using pure carbon dioxide in packed column supercritical fluid chromatography with independent pressure and flow control

Summary

Packed column supercritical fluid chromatographs (SFC) with independent control of pressure and flow produce constant efficiency but suffer from variable response factors when using a post column split into a mass sensitive detector. Most of the flow passes through a backpressure regulator, but a small fraction of the flow passes through a fixed restrictor in the base of a detector like the FID. Since the flow through a fixed restrictor increases with pressure, a changing split ratio into the detector and non-linear response results. For samples requiring a pressure program to elute both light and heavy components, distorted mass distribution measurements result.

A simple correction for this variable response is presented. Restrictor flow is a linear function of pressure. Division of the FID detector signal by the current pressure corrects for variations in post column split ratios. The correction only works for constant mass flow pumps and does not work for mixed fluids, syringe pumps or reciprocating pumps with inadequate compressibility compensation.