retention time

Retention time ( tR), also called the total  retention time. The time between injection  and the appearance of the peak maximum. The total retention volume (VR) is determined  by multiplying the retention time  by the flow rate. The adjusted retention  time (tR') adjusts for the column void volume;  tR' =  tR -  tM. 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..