4.2.2 Summarizing Solute Retention

The nature of the interaction of a solute with a given stationary phase is generally van der Waals forces. It would be quite cumbersome to constantly refer to these interactions, their functional form and magnitude, directly. It is more succinct to communicate the interaction via parameters based on the retention a phase causes for a given solute.

• Retention Time (RT): The absolute time taken by a compound to travel from the injector through the column to the detector. This is very dependent on operational conditions, so it is useful only to compare retention times for various components on one instrument for experiments performed with the same conditions. It is not meaningful to compare rentention times for different instruments.
• Relative Retention Time(RRT): Retention times can be calculated relative to the retention time of a specific compound. This can be useful for comparing retention data from one instrument to another, provided the operational parameters are the same.
• Retention Index (RI): The most general rentention parameter, this is a scale developed from the retention of straight chain hydrocarbons by a given phase.
  • The only thing that needs to be known to compare retention indices of different compounds is the stationary phase. This makes it useful to compare rentention data collected on different instruments for experiments done with different conditions.
  • The RI scale is a linear construction that defines the RI of n-C $_{\textrm{10}}$H $_{\textrm{22}}$= 1000, the RI of n-C $_{\textrm{20}}$H $_{\textrm{42}}$ = 2000, etc. That is, the RI is defined as 100*n where n is the number of carbons in a straight chain hydrocarbon. {insert figure}