SFC and Density Gradients

Scientists from Brigham Young University (Provo, Utah) and Weber State University (Ogden, Utah) used on-column spectroscopic measurements to investigate density gradients in packed capillary supercritical fluid chromatography (SFC) columns operated at the pressure drops used for solvating gas chromatography. They used Raman spectroscopy to measure the mobile phase density with respect to column position. They noted that the mobile phase linear velocity initially increased gradually and then rose rapidly near the column’s outlet. They reported that the high flow rates at the outlet were offset by a loss of solvating power and consequent decreased separation speed. They also examined the effect of fluid compressibility on SFC separations by measuring band dispersion from on-column elution profiles obtained under solvating gas chromatography conditions. The researchers found that the primary cause of band broadening was the high mobile phase velocity near the column outlet, but that significant band broadening was occurring near the column inlet as well.