Question

In the laboratory measurements are made of the gross retention time. To use this information to relate retention properties to the compound structure the adjusted retention time is required. (a) Why do the gross retention time and adjusted retention time have different values? (b) How would you determine the adjusted retention time in gas chromatography. (c) How is the adjusted retention time related to the retention (capacity) factor?

Answer 1

(a) Adjusted retention time is analyte's retention time (t_R) minus the elution time of an unretained peak (t_m).i.e. t_R'= t_R - t_M

which is also equivalent to the time the analyte spends in the stationary phase.

A solute’s retention time in chromatography is directly related to the strength of the solute’s interaction with the mobile and stationary phases. A solute’s retention time e in chromatography is directly related to the strength of the solute’s interaction with the mobile and stationary phases.

Gross retention time can be in addition of retention time (t_R) or might be total retention time of the solute.

b) The adjusted retention time in gas chromatography can be determine by analyte's retention time (t_R) minus the elution time of an unretained peak (t_m).i.e. t_R'= t_R - t_M

c) The adjusted retention time related to the retention (capacity) factor in the following way:

k’ = (t_R –t_M)/t_M (adjusted retention time (t_R' ) = (t_R - t_M )

k' =  t_R' / t_M

Capacity factor(k') is useful for comparing results obtained on different systems since it is independent on column length and flow-rate