High temperature liquid chromatography on packed capillary columns with nonaqueous mobile phases

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Abstract
The need for a high resolution chromatographic technique for analyzing compounds that are heavy, relatively polar, have low water solubility, and are not adequately separated by regular HPLC methods, has led to the development of a high temperature liquid chromatography system. The increased diffusion coefficients and reduced viscosity at higher temperatures resulted in high separation velocities and allowed long columns to be used. The HTLC system contained 70 cm columns and nonaqueous mobile phases. Packed capillary columns prevented radial temperature gradients which otherwise would reduce the efficiency. The capillary columns were packed with a reversed phase material (ODS) using supercritical carbon dioxide as the slurry fluid. A new method for preparing a ceramic frit inside the column was developed. The frit withstood pressures of at least 600 bar. The robustness of the columns in a nonaqueous environment with elevated temperature was tested and found satisfactory for 150 injections with a temperature program at each injection. Isothermal elution or temperature programming in the 50–150°C range reduced the analysis time significantly. Compounds which were completely retained at room temperature eluted with good peak shape at elevated temperature.