Refractive Index Detection Using an Ultraviolet Detector with a Capillary Flow Cell in Preparative SFC

Abstract

An ultraviolet detector with a capillary flow cell is evaluated for use as a refractive index detector in supercritical fluid chromatography (SFC) using a CO 2 mobile phase. The temperature or pressure control or both of the cell is critical to minimize density-related refractive index changes. Using CO 2 , which has a refractive index value that is significantly smaller than that of common organic solvents, leads to higher detector response. Based on a long-term noise level of 2.3 x 10 -5 refractive index units, the detection limit for n-hexadecyl alcohol at a signal-to-noise ratio of 2 is 30 μg on a 4.6-mm i.d. packed column. This corresponds to the actual detection limit of 30 ng in the capillary cell (at a split ratio of 1 :1000). The linear dynamic range of the detector is more than 2 orders of magnitude. This detection method can readily be used for preparative SFC.