Relative retention times
You can use relative retention times to check if the identification of your compounds is correct. The retention time of a compound is compared to the retention time of another specific given compound (also referred to as RRT reference). The ratio of the two retention times, that is, the relative retention time RRT, is normally a known number which you can provide in the application.
The RRT values themselves have no impact on the compound identification. Only the absolute expected retention times are used for this purpose. They are either specified in the processing method as absolute time values or calculated from relative retention times. Time reference compounds or method updates may be used to correct these absolute retention time windows based on possible shifts.
The following example shows the identification parameters for an RRT reference compound with an associated compound.
If you change the expected RT of the associated compound, its RRT value will automatically be recalculated. Also vice versa, if you change its RRT value, its expected RT will be recalculated.
If you change the expected RT of the RRT reference compound, the system recalculates the expected RT of the associated compounds.
If you use time reference compounds with RRT reference compounds, the retention time shift is applied to the RRT reference compound (see Calculations for time reference compounds). The system recalculates the expected RT of the associated compound so that the RRT values do not change.
You can also use the Update RT function with RRT reference compounds. However, you can only configure the update parameters for the RRT reference compounds. The associated compounds are forced to use the same values as their references, so that the RRT values do not change.
For not identified peaks, there is no associated compound. In this case, the first RRT reference compound is used to calculate the RRT value.