Novel pressure control in supercritical fluid chromatography using a resistively heated restrictor

Abstract

An alternative means of independently controlling column pressure in supercritical fluid chromatography (SFC) by resistively heating the post-column restrictor is demonstrated. Compared to conventional block heating methods, resistive restrictor heating provides at least four times greater pressure programming rates and allows for much faster cooling times in between runs, thereby increasing sample throughput. When applying resistive restrictor heating in proximity to a flame ionization detector, the chromatographic baseline noise increases substantially and obscures peaks. However, adding about 100 mL/min of nitrogen into the flame burner essentially removes this noise and returns the detector response to normal. The analyte retention time in consecutive pressure gradient trials reproduces well with a minimal relative standard deviation of 0.36% (n = 3). The resistive restrictor heating technique presented is also found to be equally effective for either capillary or packed SFC operating modes. Results suggest that this method can potentially provide a simple, inexpensive, and convenient alternative to limited passive restrictors or more costly and complex backpressure regulators that are often used to maintain system pressure in supercritical fluid chromatography.