The impact of placement, experimental conditions, and injections on mass flow measurements in supercritical fluid chromatography

Abstract

In supercritical fluid chromatography (SFC), the variation of pressure, temperature and volumetric flow-rate is most noticeable when the mobile phase contains only neat carbon dioxide. This can be explained by the compressibility of CO2 and introduces several difficulties to the work of chromatographers. The only flow parameter that is considered to be constant across the SFC system is the mass flow-rate. It has been shown that the Coriolis flow meter (CFM) provides different types of information depending on its placement in the instrument. Therefore, the goal of this paper is to investigate several factors affecting the variation of mass flow-rate in SFC, including four different configurations around the column, four sets of experimental conditions along with two columns and a zero-volume union. The effect of disturbances introduced by injections are studied as well. The results show different mass flow-rates when taken at the inlet or the outlet of the column. In addition, different columns produced different tendencies of variations. Study of the injections showed that the initial severe drop of mass flow is reduced when the averages are taken until the elution times of the chosen compounds. Additional testing related to possible leaks and CFM calibration showed that even if all standard operating procedures are strictly followed, reproducibility of the mass-flow rate can still be an issue.