The formation of in-situ coatings on the packing in HPLC or on capillary walls in CE by adding a substance to the mobile phase that adsorbs onto (or absorbs into) the packing or at the wall surface. The purpose of a dynamic coating is to generate a new stationary phase or to deactivate the packing material or capillary wall to prevent unwanted interactions. One simple example is the adjustment of the mobile phase or running buffer to less than pH 3 to protonate silanols and negate their effect. Another example is coating the phase with a hydrophilic polymeric material to prevent adsorption of proteins.