THE CONTRIBUTION OF THE PRESSURE-DROP TO ANALYTE RETENTION IN COUPLED-COLUMN SUPERCRITICAL-FLUID CHROMATOGRAPHY OF LIPIDS

This paper reports the qualitative and quantitative effects of the col umn pressure drop on the retention of lipid components in a serially c oupled capillary column SFC system. The contribution of the pressure d rop consists of two components, the density effect and the flow effect . The magnitude of the flow effect, i.e. the change in retention which results from changes in the flow-rate when column pressures are chang ed, is determined by the difference in single column analyte k values. The effect will be positive compared with the uncorrected retention v alues when the column with largest k values is closest to the injector . With the columns in reversed order, the effect will be negative. The contribution from the density effect always resulted in larger couple d column k values and was in most instances of more significance than the flow effect component. Values calculated with and without pressure drop correction have been compared and it has been shown that for mos t of the eighteen model lipid compounds investigated, the deviations f rom the experimental retention factors were smaller when pressure drop corrections were made.