Three quality criteria are introduced to evaluate the efficiency of fractionation by AFFF. Firstly, the resolution factor R S is given by (Eq. 3) and describes the degree of separation between two species. R S increases with a higher difference in retention times (∆t R ) and decreases with the peak widths ω i as defined by the half maximum at full width. At a resolution of 1.5, the peaks are baseline-resolved.