Prior to the development of ultra-high power liquid chromatography systems, the upper pressure limits and flow rate ranges that could be tested were limited by the power range of currently available HPLC hardware.With the advent of ultra-high power chromatography systems, the performance of the columns analyzed has been explored both theoretically and experimentally.Historically, plate height has been used as the measure for separation efficiency.However, in a practical sense, this measure is best used for isocratic and isothermal based separations.Peak capacity is a more suitable measure of efficiency in gradient separations as it considers the partitioning effects from the change in solvent strength during an analysis.For a given gradient time, peak capacity has been shown to increase beyond the predicted optimum based on the van Deemter equation, when flow rates are extended past optimal linear velocity.