Transfer Kinetics of Polar Organic Compounds over Polyethersulfone Membranes in the Passive Samplers Pocis and Chemcatcher

Abstract

Passive samplers for polar organic compounds often use a polyethersulfone (PES) membrane to retain the particulate sorbent material (e.g., in a POCIS; polar organic chemical integrative sampler) or to reduce the sampling rate and thus extend the kinetic regime (e.g., in a Chemcatcher). The transport kinetics over the PES membrane are evaluated here in a short-term (6 days) and a long-term (32 days) experiment with POCIS and Chemcatchers. Passive samplers were placed in a channel with flowing river water that was spiked with 22 organic chemicals including pharmaceuticals, pesticides and biocides; with logK(ow) (logarithmic octanol-water partitioning coefficient) values between -2.6 and 3.8. Samplers were removed at intervals and membranes and sorbent material were extracted and analyzed with LC-MS/MS. Uptake kinetics of the compounds fell between two extremes: (1) charged chemicals and chemicals of low hydrophobicity did not accumulate in PES and rapidly transferred to the sorbent (e.g., diclofenac) and (2) more hydrophobic chemicals accumulated strongly in the PES and appeared in the sorbent after a lag-phase (e.g., diazinon and diuron). Sorption kinetics were modeled with a three-compartment first-order kinetic model to determine uptake and elimination rate constants and partitioning coefficients. Water PES partitioning coefficients fitted with the model correlated well with experimentally determined values and logK(ow). Sampling rates of Chemcatcher (0.02-0.10 L/d) and POCIS (0.02-0.30 L/d) showed similar patterns and correlated well. Thus the samplers are interchangeable in practical applications. Longer lag-phases may pose problems when calculating time-weighted average aqueous concentrations for short passive sampling windows and for a correct integrative sampling of fluctuating concentrations.

Overview of the Chemcatcher® for the passive sampling of various pollutants in aquatic environments Part A: Principles, calibration, preparation and analysis of the sampler

“…From these results, the authors concluded that analytes first adsorbed onto the membrane, then diffused through the membrane and finally accumulated on the disk. These results were in accordance with other observations showing that the use of a membrane induces a lag-time between sampler deployment and the beginning of accumulation [37,61]. Vermeirssen et al [61] observed a lag phase for compounds with log K ow higher than 2.0 (diuron and diazinon).…”

“…These results were in accordance with other observations showing that the use of a membrane induces a lag-time between sampler deployment and the beginning of accumulation [37,61]. Vermeirssen et al [61] observed a lag phase for compounds with log K ow higher than 2.0 (diuron and diazinon). Two experiments were conducted for 6 and 32 days and the estimated lag phases were slightly different, probably as a result of a temperature variation between the experiments (20.5°C and 13.8°C, respectively).…”

“…Firstly, Empore disks employed without membrane accumulate a wider range of analytes with higher sampling rate values (Fig. 4) [61]. Indeed, for a range of highly hydrophobic compounds (bromodiphenylethers, the insecticide DDT and its metabolites), the use of a membrane over the C 18 disk lowered the accumulation 12-270 times for a LDPE membrane and 270-2500 times for a PES membrane [35].…”

“…Vermeirssen et al [61] analyzed this extract separately from the receiving phase whereas Nyoni et al [74] combined both extracts.…”

Uptake and release kinetics of 22 polar organic chemicals in the Chemcatcher passive sampler

“…In contrast, membranes are needed to retain the sorbent in a POCIS. If Empore™ disks are used without a membrane, they will sample a wider range of chemicals and with higher sampling rates [12]. Low selectivity is very important when combining passive sampling with biological analysis, to prevent exclusion of unknown toxicants [13].…”