On the Calculation of the Stationary Phase Volume in Reversed Phase Chromatography

Abstract

The volume phase ratio (stationary/mobile, V_s/V_m) in reversed phase liquid chromatography (RPLC) is a necessary quantity for obtaining thermodynamic information such as chromatographic partition coefficients and changes in entropy and Gibbs free energy as a solute partitions from the mobile to the stationary phase. Previous methods of calculating this ratio have used only the surface area of the bonded stationary phase or have overestimated the stationary phase volume by including that of the inert silica support. A new method is presented for the calculation of the stationary phase volume, V_s, which only requires measurements of carbon load and the total weight of packing in the column. A primary advantage of this method is that knowledge of the packing surface area is not necessary. When calculated by this method, V_s is the actual volume of the alkyl chains bonded to the support surface, but neglects intercalated solvent volumes.