Linear solvation energy relationships regarding sorption and retention properties of hydrophobic organic compounds in soil leaching column chromatography

The capacity factors of a series of hydrophobic organic compounds (HOCs) were measured in soil leaching column chromatography (SLCC) on a soil column, and in reversed-phase liquid chromatography on a C₁₈ column with different volumetric fractions (φ) of methanol in methanol-water mixtures. A general equation of linear solvation energy relationships, log(XYZ) = XYZ₀ + mV_I/100 +π* + bβ_m + aα_m, was applied to analyze capacity factors (k′), soil organic partition coefficients (K_oc) and octanol-water partition coefficients (P). The analyses exhibited high accuracy. The chief solute factors that control logK_oc, logP, and logK′ (on soil and on C₁₈) are the solute size (V_I/100) and hydrogen-bond basicity (β_m). Less important solute factors are the dipolarity/polarizability (πr*) and hydrogen-bond acidity (α_m). Log k′ on soil and log K_oc have similar signs in four fitting coefficients (m, s, b and a) and similar ratios (m:s:b:a), while k′ on C₁₈ and logP have similar signs in coefficients (m, s, b and a) and similar ratios (m:s:b:a). Consequently, log k′ values on C₁₈ have good correlations with logP (r > 0.97), while log k′ values on soil have good correlations with logK_oc (r > 0.98). Two K_oc estimation methods were developed, one through solute solvatochromic parameters, and the other through correlations with k′ on soil. For HOCs, a linear relationship between logarithmic capacity factor and methanol composition in methanol-water mixtures could also be derived in SLCC.