In accordance with one aspect of the present invention, an ultra-high pressure chromatography system (UHPLC) is provided and includes a high pressure chromatography arrangement of equipment (HPLC system) as well as a UHPLC module for converting the HPLC system into the UHPLC system. One exemplary module includes a gradient storage column fluidly connected to the HPLC equipment in a post injector manner such that an injection plug can be selectively delivered and stored, in an inverted manner, therein at low pressures, while stored injection plug (gradient) is delivered to an analytical column using higher pressures for chromatographic separation.