Partitioning of Organic Chemicals to Polyacrylate-Coated Solid Phase Microextraction Fibers: Kinetic Behavior and Quantitative Structure−Property Relationships

The solid phase microextraction technique uses polymer-coated fused-silica fibers to extract organic chemicals from an aqueous or gaseous phase. In the current paper, the partitioning behavior of organic chemicals from water to polyacrylate coating is described in terms of a two-compartment model and first-order kinetics. Experimental results show that, through agitation, it is possible to achieve a sufficiently small aqueous diffusion layer around the fiber to prevent aqueous diffusion from being the limiting factor in the absorption process. This then implies that the equilibration time is completely determined by the polyacrylate phase. In addition, the kinetic rate constants derived from the experimental results, viz. the uptake rate constant and polyacrylate−water partition coefficient, are modeled by multivariate techniques, using physicochemical and quantum chemical descriptors. These models clearly show that, besides hydrophobicity expressed as the octanol−water partition coefficient, the energy of the lowest unoccupied molecular orbital (and related properties) and the most positive charge on any hydrogen atom in the molecule are important descriptors. This indicates that hydrogen bonding plays a significant role in polyacrylate−water partitioning. The models that are presented can be used to predict absorption profiles of organic chemicals to polyacrylate-coated fibers, thereby giving the opportunity to predict the kinetics (including equilibration times) by computations alone.