The standard procedure for solute descriptor determination was as follows. First, the system parameters in eq 1 were calibrated for each column (or partition system) and temperature by MLR using log k' or log K data for reference compounds. Solute descriptor values for the reference compounds are presented in Table . Dimethylformamide, 1-pentylamine, dimethylsulfoxide, and dodecamethylcyclohexasiloxane (D6) were removed from the log k' data sets, because they frequently appeared as outliers (>3 SD) of the PP-LFER model fit. Reference data sets for hexadecane/water partition coefficients (KHxd/w), Kow, and octanol/air partition coefficients (Koa) were taken from the cited references and amended with data for organosilicone compounds The solute descriptors for PFAS were then backcalculated using the calibrated PP-LFER equations. Of the five descriptors, V can be calculated from the molecular structure, and L was available for the PFAS studied. Thus, the left side of eq 2 below was known, and MLR was performed to obtain S, A, and B on the right side.