Effect of the Cooling Coefficient on Efficiency Loss in SFC

Abstract

Supercritical fluid chromatography (SFC) is becoming a rapid alternative to high performance liquid chromatography (HPLC) because the lower viscosity and higher diffusivity of the mobile phase due to critical conditions enables faster separations and the ability to use smaller stationary phase particle sizes. However, radial temperature gradients that form from expansion of the mobile phase across the column reduce its efficiency. The net cooling coefficient of the mobile phase at the column outlet is a major factor controlling that temperature drop. The experimental correlation between the net cooling coefficient and efficiency loss was examined by performing two series of experiments: one where the oven temperature was held constant at 50.0 °C and the column outlet pressure was varied to yield nominal net cooling coefficients ranging from 0.10 to 0.25 K/bar and another where the column outlet pressure was held constant at 148 bar and the oven temperature was varied to yield the same range of nominal net cooling coefficients. Plate height curves of both sets of experiments were produced to examine column efficiency. It was found that the elution profiles that shared the same net cooling coefficient but had different experimental conditions had nearly identical column efficiencies, indicating that the net cooling coefficient strongly predicts column efficiency.