Figure 28 : NOTE: k = ts / tm. In PLC all separation happens during the dead time tm, during which nothing is eluted from an isocratic HPLC column (Nothing is programmed. Iso baric, isothermal, constant phase composition) . Other name for dead time: hold-up time within the column. If we want to eluate a substance from the stationary bed we need an additional time ts. One may call ts the net retention time or the residence time in the stationary phase. See figure 29. The measurable total residence time in the mobile AND stationary phase or the non adjusted retention time is tms = tm+ ts. So simple.