The study of the characteristics of packing material for preparative liquid chromatography

The study of the characteristics of packing material for preparative liquid chromatography was carried out on two types of commonly used stationary phases: the octadecyl-bonded silica adsorbents (ODS) for Reversed Phase Liquid Chromatography (RPLC) and the ion exchange resins for Ion Exchange Liquid Chromatography (IXLC).

For RPLC, an overall look at the column performance reproducibility was made first by packing a series of five columns with the same stationary phase and under the same conditions. Four 10 µm spherical C₁₈ stationary phases were used: KROMASIL, VYDAC, YMC and ZORBAX. The retention factors, column efficiencies, and equilibrium isotherms were determined for a series of compounds and the results were compared. It was found that these columns have significantly different performance. The source for this irreproducibility was investigated from the packing density view point, which in part was done by applying Inverse Size Exclusion Chromatography (ISEC) to determine the column external porosity. As a result, the column external porosity varies from column to column. This study was followed by packing more columns with the same stationary phase but under various packing pressures. It was found that the column external porosity decreases and packing weight increases as the packing pressure increases. Isotherm parameters obtained on one column, after being modified by the respective packing volumes or weights, can be applied to another to predict band profiles with satisfactory accuracy.

For IXLC, the emphasis was put on the mass transfer kinetics between proteins and the ion exchanger stationary phase. One Tosohaas DEAE-5PW TSK-Gel and two Pharmacia RESOURCE-Q anion exchange columns were used. Breakthrough curves were acquired for the determination of the equilibrium isotherm on each column. An average rate coefficient of the mass transfer kinetics was determined for each breakthrough curve by applying a lumped kinetic model coupled with the ideal model of the mass balance equation in liquid chromatography. This rate coefficient was found to increase linearly as the average sample concentration increases. The column performance reproducibility study in IXLC was made on the two identical RESOURCE-Q columns (same code number but different lot number). Their thermodynamic properties were found to be significantly different from each other, indicating the difficulties one might encounter in the future if preparative liquid chromatography is to become a major technique of separation in the pharmaceutical industry.