Absorption of hydrophobic compounds into the poly(dimethylsiloxane) coating of solid-phase microextraction fibers: High partition coefficients and fluorescence microscopy images

The use of solid-phase microextraction with poly(dimethylsiloxane) (PDMS)-c oated glass fibers for the extraction and analysis of hydrophobic organic a nalytes is increasing. The literature on this topic is characterized by lar ge discrepancies in partition coefficients and an uncertainty of whether hi ghly hydrophobic analytes are retained by absorption into the fiber coating or by adsorption to the fiber surface. We applied a new method, which mini mizes the impact of experimental artifacts, to determine PDMS water partiti on coefficients of 17 hydrophobic analytes including chlorinated benzenes, PCBs, PAHs, and p,p'-DDE. These partition coefficients are several orders o f magnitude higher than some reported values. Two observations strongly sug gest that the retention of hydrophobic organic substances is governed by pa rtitioning into the PDMS coating, (1) The partition coefficients are propor tional with octanol/water partition coefficients, (2) The fluorescence of f luoranthene was observed to be homogeneously distributed within the polymer coating when studied by means of fluorescence microscopy, Implications of these findings for the application of solid-phase microextraction with resp ect to potential detection limits, with respect to biomimetic extraction, a nd with respect to measurements in multicompartment systems are discussed.