Solid phase microextraction speciation analysis of triclosan in aqueous media containing sorbing nanoparticles

Abstract

Environmental context. Speciation analysis of organic compounds in aquatic media is often performed using solid phase microextraction with the assumption that only the free organic form is accumulated. We show that in the presence of silica nanoparticles, this interpretation is confounded by partitioning of nanoparticulate-bound compounds between water and the solid phase, as well as their aggregation at solid-bulk medium interfaces. Equilibrium measurement of the target analyte is feasible if the solid phase is protected by a suitable membrane.Abstract. Solid phase microextraction (SPME) is applied in the speciation analysis of the hydrophobic compound triclosan in an aqueous medium containing sorbing SiO 2 nanoparticles (NPs). It is found that these NPs, as well as their complexes with triclosan, partition between the bulk medium and the solid phase poly(dimethylsiloxane) (PDMS). Furthermore, they appear to aggregate at the PDMS-water interface. The total triclosan concentration in the solid phase thus includes both the free and the NP-bound forms. Proper computation of the analyte concentration in the sample medium requires (i) consideration of the speciation of triclosan inside the solid phase and (ii) elimination of the effects of aggregation of NP complexes at the solid phase-bulk medium interface. Possible solutions include application of a protective membrane with pore size smaller than the NP diameter. This allows measurement of the free triclosan concentration, albeit at the cost of longer accumulation times and loss of kinetic information on the triclosan-NP complex.Additional keyword: SPME.

Polyelectrolyte coatings prevent interferences from charged nanoparticles in SPME speciation analysis

“…Based on measurements for the samples containing triclosan only, an equilibrium partition coefficient of TCS between water and solid phase, K sw;TCS , of 5 Â 10 2 was determined. This value of K sw;TCS is similar to the one obtained for native PDMS [18] which indicates that the polyelectrolyte bilayer did not influence its extraction characteristics. Detailed description of the temporal evolution of the mean total triclosan concentration in the unmodified solid phase is presented and discussed in [15].…”

“…The experimentally measured value of k TCS in the absence of SiO 2 nanoparticles is found to be 1.1 Â10 À3 s À1 which is in good agreement with the value found for non-modified PDMS [18]. This allows us to conclude that diffusion through the PDDA/PSS layer at the PDMS surface (a few nanometers thick [27]) does not significantly reduce the rate of mass transfer from the sample medium into the solid phase.…”

“…at its surface which are measured together with the extracted free triclosan [15]. One of the proposed solutions to avoid interferences due to sorbing nanoparticles is the application of a protective membrane with a pore size smaller than the nanoparticle diameter [18]. This, however, has the drawback of prolongation of the SPME equilibration time and loss of kinetic information from the temporal accumulation profile.…”

“…In fact, the polyelectrolyte-modified solid phase neatly extracts the amount of TCS that corresponds to the triclosan speciation in the aqueous phase and reflects its free concentration (equal to 55% of total TCS [18]). The temporal curves exhibit the expected shape of an approximately exponential accumulation function (see dashed lines in Fig.…”

“…Therefore, a substantial number of studies have been devoted to search for ways to improve the performance of SPME in complex samples. Solutions like sample pretreatment and clean-up, preparation of new biocompatible extraction phases [16,17] and employment of a protective membrane around the solid phase [18] have been suggested.…”