2025 Volume 46 Issue 3 Pages 145-151
The retention of ethane in cryogenic high performance liquid chromatography (HPLC) at -196 °C was investigated by comparing with the retentions in ambient temperature gas chromatography (GC) at 50 °C (analyte: n-pentane) and ambient temperature HPLC at 25 °C (analyte: acenaphthene) using commercially available linear (trimethyl, dimethyl-n-butyl, dimethyl-n-octyl, and dimethyl-n-octadecyl silica) and laboratory-made branched alkyl chain (dimethylisopropyl and dimethylthexyl silica) stationary phases. For this investigation, the densities of the functional and end capping groups were evaluated using the carbon and hydrogen contents in the packing materials, as measured by CHNS analysis. To evaluate retention in each stationary phase and separation mode, the retention factor per single functional group and the retention per single carbon unit (CH2 or CH3) were calculated. A detailed study on the retention behavior revealed that the retention behavior observed with linear alkyl chain stationary phases in cryogenic HPLC was similar to that in ambient temperature GC, but not ambient temperature HPLC. The stationary phase of the branched thexyl group resulted in a weak interaction for the test analytes in HPLC-196°C and HPLC25°C. By contrast, the stationary phase of the isopropyl group did not suppress the analyte retention in either liquid chromatography.
