ACS Instrument Practice Test

In chromatography, the times tR and t0 are used to quantify how long an analyte interacts with the column compared to the mobile phase. The retention time tR is the time from injection to when the analyte is detected, reflecting how long the analyte spends traveling through the column (including both mobile and stationary phase interactions). The dead time t0, also called the void time, is the time it takes for an unretained species to pass through the column, representing the portion of the run that involves only the mobile phase with no interaction with the stationary phase. In retention-factor calculations, k = (tR − t0)/t0, so tR is the retention time and t0 is the dead time. This is why the correct interpretation labels tR as the retention time of the analyte and t0 as the time for the unretained compound to pass through.