Calibration of a passive sampler based on stir bar sorptive extraction for the monitoring of hydrophobic organic pollutants in water

Abstract

A passive sampler based on stir bars coated with polydimethylsiloxane (PDMS) was calibrated for the measurement of time-weighted average concentrations of hydrophobic micropollutants, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls and organochlorine pesticides, in water. Stir bar/water partition coefficients were measured by equilibrating bars with sheets made of silicone rubber material for which partition coefficients had been reported previously. Kinetic parameters characterising the exchange of analytes between stir bars and water were determined under controlled exposure conditions using a passive dosing system. The dosing system consisted of silicone rubber sheets with a large surface area, spiked with analytes. During stir bar sampler exposure, analytes partitioned from dosing sheets to water in the exposure tank and maintained constant exposure concentrations. Reversible and isotropic exchange kinetics of analytes between sampler and water was confirmed by measuring the release of a range of performance reference compounds (PRCs) from stir bars. Application of a two-resistance model confirmed that, except for hexachlorocyclohexane isomers, uptake of the test compounds under the experimental conditions was controlled by diffusion in the water boundary layer. This permits the application of PRCs for in situ calibration of uptake kinetics of test compounds to stir bars.