How Do C18 HPLC Phases Differ ?

Reversed phase HPLC columns which utilize the octadecyl functional group often differ in many ways. Besides the particle size and shape of the stationary phase (irregular or spherical), other parameters must be considered including: Porosity (fully porous or superficially porous) the coating chemistry and degree of end-capping used. Two other very important ways that columns can differ from one another are in their available surface area and the extent to which those surfaces are covered with the phase coating (i.e. covalently bonded or non-covalently coated onto the support, plus the total carbon %). When comparing columns for use in validated methods, be sure and consider these factors to minimize the number of changes to your method. Always test several columns of the same exact type to determine the batch-to-batch reproducibility and variation. Some manufacturers have mastered the art of preparing and packing columns which achieve high batch-to-batch reproducibility. After all, what good is a specific column in your method if the results are not reproducible ?