The volume of mobile phase entering the column between the start of the @E02042@ and the emergence of the peak maximum, or the corresponding time. In most of the cases, this is equal to the total retention volume (time). There are, however, cases when the @E02042@ process does not start immediately at sample introduction. For example, in liquid @C01075@, sometimes the column is washed with a liquid after the application of the sample to displace certain components which are of no interest and during this treatment the sample does not move along the column. In gas @C01075@, there are also cases when a liquid sample is applied to the top of the column but its @E02042@ starts only after a given period. This term is useful in such cases.