Total retention time (\(t_{\rm{R}}\)) minus hold-up time (\(t_{\rm{M}}\)). \(t_{\rm{R}}^{\prime} = t_{\rm{R}} - t_{\rm{M}}\)
Source:
PAC, 2017, 90, 181. 'Terminology of separation methods (IUPAC Recommendations 2017)' on page 196 (https://doi.org/10.1515/pac-2017-0111)