Retention time
The retention time (tR) is the time that each analyte needs to go from the injector to the detector. It is normally calculated from the injection moment (t=0) until the maximum of the peak, when most of the molecules reach the detector (t=tR) indicated by the highest point of the peak.
This retention time is dependent on the affinity between the analyte and the mobile and stationary phase. The more the analyte interacts with the stationary phase, the longer the retention time is. In contrast, the more the analyte interacts with the mobile phase, it will be eluted fast and hence the retention time will be short.