The concentration region at which the solvent is formed during in situ solvent formation microextraction is determined by varying the concentrations of the two components required to form a solvent. In particular, a solvent is formed in situ during ion-associate phase (IAP) microextraction by mixing an aqueous solution with an organic cation and an organic anion. In this study, benzethonium chloride (BenCl) and sodium ethylbenzenesulfonate (NaEBS) were employed as the organic cation and anion sources of model IAPs to thoroughly investigate the in situ solvent formation. Additionally, the formation of the IAPs and the solvent via centrifugation of the formed ion associates was examined. We demonstrated that ion associates are formed when the product of [EBS] and [Ben] is greater than the solubility product and [EBS] is greater than [Ben]. The highest extraction of polycyclic aromatic hydrocarbons (PAHs) was achieved with an amount of NaEBS 40 times greater than that of BenCl. A higher hydrophobicity in the IAP extraction of PAHs, estrogens, and pesticides facilitated extraction into the IAP.

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