Comparison of solid phase microextraction geometries for effective preconcentration of volatile per- and polyfluoroalkyl substances

Neutral per- and polyfluoroalkyl substances (PFAS) serve as precursors to perfluorinated acids, and their transformation contributes to the ongoing release of legacy PFAS contaminants into the environment. The accurate and efficient extraction of neutral, volatile PFAS remains a critical analytical challenge. In this study, we evaluated the impact of solid phase microextraction (SPME) geometry and agitation methods on extraction performance using SPME-fiber and SPME-arrow devices in headspace (HS) and direct immersion (DI) extraction modes. Agitation of the samples during extraction was conducted with a cycloid-shaped Heatex agitator at 600 rpm and compared to an orbital shaker at 250 rpm. Results demonstrated that SPME-arrow devices offered enhanced sensitivity and broader linear dynamic ranges for fluorotelomer alcohols such as 1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluoro-1-hexanol (4:2 FTOH). In contrast, SPME-fibers showed improved response for hydrophobic, semi-volatile analytes such as <i>N</i>-methylperfluorooctanesulfonamidoethanol (MeFOSE) with lower limits of quantitation (0.005 μg L^-1-0.25 μg L^-1). The influence of extraction mode on SPME-geometry was systematically investigated with residual plots (DI-HS) reaffirming the propensity for extraction by DI of hydrophobic, semi-volatile analytes and volatile analytes by HS. The Heatex agitator improved extraction efficiency for diffusion-limited compounds by enhancing convective mixing and reducing mass transfer resistance in the boundary layer. Extraction time profiles suggested the occurrence of competitive adsorption at extraction times longer than 35 min. These findings underscore the importance of tailoring SPME parameters - agitation type, extraction mode, time, and sorbent geometry - when developing sample preparation workflows for analysis of neutral volatile PFAS.