Also called the total retention time. The time between injection and the appearance of the peak maximum. The total retention volume (V_R) is determined by multiplying the retention time by the flow rate. The adjusted retention time (t_R´) adjusts for the column void volume; t_R´ = t_R – t_M. It usually is measured from the point of injection to the apex of the peak, but it should be measured to the center of gravity of the peak for asymmetric peaks.