Quantitative evaluation of polyethersulfone and polytetrafluoroethylene membrane sorption in a polar organic chemical integrative sampler (POCIS)

Abstract

The lag effect in the polar organic chemical integrative sampler (POCIS) equipped with a polyethersulfone (PES) membrane (POCIS-PES) is a potential limitation for its application in water environments. In this study, a POCIS with a poly(tetrafluoroethylene) (PTFE) membrane (POCIS-PTFE) was investigated for circumventing membrane sorption in order to provide more reliable concentration measurements of organic contaminants. Sampler characteristics such as sampling rates (R_S) and sampler-water partition coefficients (K_SW) were similar for POCIS-PES and POCIS-PTFE, indicating that partitioning into Oasis HLB as the receiving phase dominates the overall partitioning from the aqueous phase to the POCIS. Membrane sorption was quantified in both laboratory and field experiments. Although POCIS-PTFE showed minor membrane sorption, the PTFE membranes were not robust enough to prevent changes in the sorption of the pollutants to the inner Oasis HLB sorbent due to biofouling. This was reflected in significant ionization effects in the electrospray ionization (ESI) source during the LC-MS/MS analysis. Despite clear differences in the ionization effects, the two POCISs types provided similar time-weighted average (C_TWA) concentrations after a two-week passive sampling campaign in surface water and the outflow of a wastewater treatment plant. This study contributes to a more detailed understanding of POCIS application by providing a quantitative evaluation of membrane sorption and its associated effects in the laboratory and field.