Optimization of the polar organic chemical integrative sampler for the sampling of acidic and polar herbicides

This paper presents an optimization of the pharmaceutical Polar Organic Chemical Integrative Sampler (POCIS-200) under controlled laboratory conditions for the sampling of acidic (2,4-dichlorophenoxyacetic acid (2,4-D), acetochlor ethanesulfonic acid (ESA), acetochlor oxanilic acid, bentazon, dicamba, mesotrione, and metsulfuron) and polar (atrazine, diuron, and desisopropylatrazine) herbicides in water. Indeed, the conventional configuration of the POCIS-200 (46 cm² exposure window, 200 mg of Oasis® hydrophilic lipophilic balance (HLB) receiving phase) is not appropriate for the sampling of very polar and acidic compounds because they rapidly reach a thermodynamic equilibrium with the Oasis HLB receiving phase. Thus, we investigated several ways to extend the initial linear accumulation. On the one hand, increasing the mass of sorbent to 600 mg resulted in sampling rates (R _s s) twice as high as those observed with 200 mg (e.g., 287 vs. 157 mL day^?1 for acetochlor ESA). Although detection limits could thereby be reduced, most acidic analytes followed a biphasic uptake, proscribing the use of the conventional first-order model and preventing us from estimating time-weighted average concentrations. On the other hand, reducing the exposure window (3.1 vs. 46 cm²) allowed linear accumulations of all analytes over 35 days, but R _s s were dramatically reduced (e.g., 157 vs. 11 mL day^?1 for acetochlor ESA). Otherwise, the observation of biphasic releases of performance reference compounds (PRC), though mirroring acidic herbicide biphasic uptake, might complicate the implementation of the PRC approach to correct for environmental exposure conditions.