Silicone rubber selection for passive sampling of pesticides in water

Abstract

Silicone rubber can extract organic compounds with a broad range of polarities (logKow>2-3) from aqueous samples. Such compounds include substances of major concern in the protection of aquatic ecosystems and human health, e.g. pesticides. Silicone rubbers (SRs) with various characteristics have been successfully used in sorptive methods for water sample extraction in the laboratory (SPME, SBSE), and for passive sampling in aquatic environments. However, only few studies have evaluated variability in organic compound sorption due to the origin of SRs, particularly for pesticides. The aim of this study was to select an SR for the extraction of pesticides from water samples by passive sampling. To this end we measured the impact of seven SR formulations on sorption capacity, defined by the partition coefficient (Ksw). Kinetic experiments and sorption isotherms were performed to determine extraction recovery as a selection criterion for SRs, and pesticide partition coefficients. Very large differences in affinity for pesticides were found between two kinds of SRs: "Polymerized SR kits" and "Manufactured SRs". One SR was chosen among the "Manufactured SRs", and the Ksw values of 21 pesticides were determined, filling a gap in the literature (1.50<logKow<5.51). In light of sorption properties, literature data and additional economic and technical factors, we suggest using SR from Goodfellow in future work to reduce the variability of Ksw literature values.

Calibration of silicone rubber rods as passive samplers for pesticides at two different flow velocities: Modeling of sampling rates under water boundary layer and polymer control

“…This silicone rubber had been selected in an earlier study for its sorption properties for pesticides [13]. The rod shape was preferred to the classic sheet because of the convenience of handling and storage, the lower volume of solvent required for backextraction, and the possibility of using thermodesorption-gas chromatrography (TD-GC)/MS analysis.…”

“…Before use, silicone rubber rods were chemically and thermally cleaned to remove most residues such as oligomers that could interfere with the instrumental analysis [13]. First the silicone rubber rods were chemically conditioned by immersion in dichloromethane/methanol (50/50, v/v) under sonication for 15 min.…”

“…For more apolar pesticides, spiked silicone rubber sheets acted as diffusive contaminant sources in the water [5,10]. The quantity of pesticides absorbed by the sheets was assessed with partition coefficients determined by Martin et al [13]. The total volume of the dosing sheets was 20 times that of the silicone rubber rods, ensuring that depletion caused by uptake would be negligible.…”

“…The solvent back-extraction recoveries of this step were between 60 and 98% depending on the compounds (listed in Table 1). Chromatographic parameters, limits of quantification (LOQs), and settings for MS/MS (Supplemental Data 1) analysis are reported elsewhere by Martin et al [13]. Before analysis the pesticides absorbed in the silicone rubber rods were desorbed in 200 mL of acetonitrile/methanol (50/50) for 15 min under sonication.…”

Flow lithography in ultraviolet-curable polydimethylsiloxane microfluidic chips

“…45 Given the fact that a viscosity ratio of X-34-4184 (2900 cP) to Sylgard 184 (5100 cP) is approximately 0.57, 34,46 the molecular weight ratio of UV-curable PDMS to thermally curable PDMS is approximately 0.45. Moreover, not only because the density of both types of the base polymer is identical to 1.03 g/ml but also because both types of PDMS are crosslinked by catalytic hydrosilyation, 47 the smaller molecular weight indicates that a greater number of precursors of UV-curable PDMS exist in a unit volume. This could induce more interfacial crosslinks and thus stronger bonding while a partially cured bottom layer continues undergoing hydrosilylation in contact with another block of UV-cured PDMS, which also appears to be consistent with other research.…”