Optimizing flash chromatography requires finding the ideal cartridge and conditions for a given sample. As the goal is to prepare the largest possible amount of pure sample in the shortest possible time and with a minimum use of solvent, it is crucial to know how high loadings affect the separation for different cartridges.
Unlike analytical chromatography, preparative separations are usually carried out under overloaded conditions, i.e. with a sample amount that is so large that it causes additional peak broadening. This is acceptable in preparative chromatography, as long as the peaks in the sample do not overlap. The maximum feasible loading for a given separation therefore depends not only on the loading capacity of the column, but also on the initial separation of the compounds of interest.
Spherical silica particles provide multiple benefits as a column material over irregularly shaped particles. They can be packed more tightly into the column, leading to more homogeneous flow, reduced peak broadening and thus higher resolution. The low content of fine particles also reduces back pressure, a property that is especially important when using smaller particle sizes. This application note gives an example of how loading affects preparative separations for a specific sample. FlashPure cartridges with particles of different sizes are compared, as well as spherical and irregular packing materials.