Unavoidable flow-rate errors in high-performance liquid chromatography

Abstract

Two different types (low-pressure mixing and high-pressure mixing) of high-performance liquid chromatographic (HPLC) solvent delivery systems were evaluated for their flow-rate accuracy using three common hydro-organic mobile phases: methanol-water, acetonitrile-water and tetrahydrofuran-water. Both systems delivered flow-rates 2-12% lower than the desired (set) values, depending on the mobile phase composition. Further investigations revealed that these errors in flow-rate were due in part to non-ideal mobile phase behavior (non-zero volumes of mixing, non-zero compressibilities, pressure dependent viscosities, and deviations from Darcy's law) and non-ideal stationary phase behavior (column expansivity and packing compression). An approach to correct for the systematic errors in flow-rate is described for binary solvent mixtures. The approach utilizes correction factors based on non-ideal mobile and stationary phase behavior and has been experimentally confirmed for the mobile phases and columns we examined. Although approximate in nature, our approach reduces the systematic errors in flow-rate about ten-fold, and provides a means for estimating the instrumental contribution to flow-rate error as well. This leaves only an instrumental bias which can be measured and then factored out for all further experiments with that instrument. The resulting improvements in flow-rate accuracy provided by our approach will be extremely useful to researchers who need very accurate retention data for physicochemical measurements as well as to HPLC manufacturers and users for quality control and troubleshooting of these solvent delivery systems. © 1989.