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The interaction properties of some alkylsiloxane-, phenylsiloxane-and cyanopropylsiloxane-bonded silica-based sorbents for solid phase extraction are characterized. The linear solvation energy relationship model is used to estimate the characteristic interaction constants of the sorbents, s (dipolarity/polarizability), a (hydrogen bonding basicity), b (hydrogen bonding acidity), r (polarizability), and l (methylene selectivity). For nonpolar alkyl-bonded sorbents, the l constant is the largest, indicating that the cavity/dispersive interactions term is the dominant term favoring retention on the sorbent. Other interaction terms play minor roles in retention. For the polar cyanopropyl-bonded sorbent the s and a constants are the largest and are essentially equal, followed by 1, r and b constants. For the phenyl-bonded sorbent, the b coefficient is the largest, followed by a quite large a coefficient. KeywordsCharacteristic interaction constant, linear solvation enerev relationship reversed-phase sorbent, solid phase extraction, gas chromatography, Solid phase extraction (SPE) is widely used to isolate and concentrate organic contaminants from water, largely replacing liquid-liquid extraction.1 A variety of silica-based sorbents with different bonded ligands are broadly used in SPE. Among these silica-based sorbents, reversed-phase sorbents with various bonded functional groups are widely used.Practicing chromatographers have noted the significant differences in retention characteristics between nominally equivalent silica-based stationary phases for reversed phase liquid chromatography (RPLC) such as C-182 and cyano-bonded materials.3 This variability comes naturally since retention in RPLC is determined by both solvophobic and chemical interactions between solute molecules and reactive sites of the stationary phase, which involve not only interactions between solute molecules and the organic bonded phase (solvophobic)4 but also hydrogen bonding interactions with unreacted silanol groups and complexation with trace metals on the silica surfaces.5 The relative contributions of these two types of interactions depends on the characteristics of the stationary phase, which include the nature of the base silica particles such as the specific surface area and pore size and volume, the nature of bonded organic ligand, and the bonding process. Chemical interactions are often regarded as undesirable since these types of interactions, in particular silanophilic interactions, are responsible for the excessive peak tailing and long retention times observed for basic solutes. The presence of these types of interactions also leads to poorer control of the column packing, resulting in column-to-column irreproducibility.4,5 As diversity in retention properties of various stationary phases due to this variability has caused many difficulties for chromatographers in selecting the best column for a given separation, knowledge of the nature and relative contributions of possible interaction between the solute and stationary phase to ...