Retention volume:

In this Unit, we shall restrict to retention volume, V_R, for our discussion. The small early peak in Figure represents a solute that is least retained through the stationary phase. It passes straight by the column without stopping. In GC, this behaviour is frequent shown through air or methane and the peak is frequent called an air peak. The symbol V_m, sometimes known as the hold-up volume or void volume, serves for measure the interstitial or interparticle volume of the column. The term dead volume, although not recommended, is also hugely used.

 t_R′ = t_R  - t₀                                                                                                              

where t_R = adjusted retention time and t₀ = retention time of air peak Thus, (t_R)  A, (t_R) B and (t_R) C are the adjusted retention times for solutes A, B, and C, respectively. Similarly

V_R =V_R-V_M

where V_R = adjusted retention volume and V_M = hold up volume and ( V_R′ ) A, (V_R′ ) B and (V_R′ ) C are the adjusted retention volumes for solutes A, B, and C, respectively.

The detector response, or field under the curve, (AUC) is proportional to the quantity of material passing by the column. Thus, a quantitative measurement could be made. For this reason, a calibration graph of AUC vs quantity of solute injected required to be constructed for each solute separately. If we refer to Figure, based on AUC, solute B is present in the largest amount, while A and C are in lesser amounts and are approximately equal.