Chromatography is a process used in science to separate mixtures. The basic principle of chromatography is that different compounds of different sizes will pass through barriers at different speeds. In high pressure liquid chromatography (HPLC), the compound is injected through a column of different sized beads. A smaller compound passes through the column faster than a larger compound. The amount of time it takes for the compound to pass through the column is the retention time (RT). The relative retention time (RRT) is the comparison of the RT of one compound to another.
Locate the main peak on the HPLC printout. The main peak will be the largest and most prominent peak in the output.
Read the RT of the main peak. This can by read by looking at when the peak starts and when it stops. If the peak starts at 6.5 minutes and ends at 9.5 minutes, then the RT is 3 minutes.
Locate the peak of interest. This can be any peak you want to calculate the RRT. Read the RT of that peak. If the peak starts at 1 minute and ends at 2.5 minutes, then the RT is 1.5 minutes.
Divide the RT of the peak of interest by the RT of the main peak to find the RRT of the peak of interest. In our case, this would be 1.5 minutes/3 minutes, or 0.5.