Equilibrium partitioning of organic compounds to OASIS HLB® as a function of compound concentration, pH, temperature and salinity

Abstract

Oasis hydrophilic lipophilic balance^® (Oasis HLB) is commonly employed in solid phase extraction (SPE) of environmental contaminants and within polar organic chemical integrative passive samplers (POCIS). In this study batch experiments were carried out to evaluate the relative affinity of a range of relevant organic pollutants to Oasis HLB in aqueous systems. The influence of sorbate concentration, temperature, pH, and salinity on the equilibrium sorption was investigated. Equilibrium partition ratios (K_D) of 28 compounds were determined, ranging over three orders of magnitude from 1.16 × 10³ L/kg (atenolol) to 1.07 × 10⁶ L/kg (isoproturon). The Freundlich model was able to describe the equilibrium partitioning to Oasis HLB, and an analysis of the thermodynamic parameters revealed the spontaneous and exothermic nature of the partitioning process. Ionic strength had only a minor effect on the partitioning, whereas pH had a considerable effect but only for ionizable compounds. The results show that apolar interactions between the Oasis HLB and analyte mainly determine the equilibrium partitioning. These research findings can be used to optimize the application of SPE and POCIS for analyses of environmental contaminants even in complex mixtures.

Keywords: Concentration; Equilibrium partitioning; Ionic strength; Oasis HLB(®); Temperature; pH.