Speciation Analysis of Aqueous Nanoparticulate Diclofenac Complexes by Solid-Phase Microextraction

Abstract

The dynamic sorption of an organic compound by nanoparticles (NPs) is analyzed by solid-phase microextraction (SPME) for the example case of the pharmaceutical diclofenac in dispersions of impermeable (silica, SiO(2)) and permeable (bovine serum albumin, BSA) NPs. It is shown that only the protonated neutral form of diclofenac is accumulated in the solid phase, and hence this species governs the eventual partition equilibrium. On the other hand, the rate of the solid/water partition equilibration is enhanced in the presence of the sorbing nanoparticles of SiO(2) and BSA. This feature demonstrates that the NPs themselves do not enter the solid phase to any appreciable extent. The enhanced rate of attainment of equilibrium is due to a shuttle-type of contribution from the NP-species to the diffusive supply of diclofenac to the water/solid interface. For both types of nanoparticulate complexes, the rate constant for desorption (k(des)) of bound diclofenac was derived from the measured thermodynamic affinity constant and a diffusion-limited rate of adsorption. The computed k(des) values were found to be sufficiently high to render the NP-bound species labile on the effective time scale of SPME. In agreement with theoretical prediction, the experimental results are quantitatively described by fully labile behavior of the diclofenac/nanoparticle system and an ensuing accumulation rate controlled by the coupled diffusion of neutral, deprotonated, and NP-bound diclofenac species.

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

“…It may be expected [6,7] that the lability of the complex triclosannanoparticulate species is determined by the rate of diffusive transport of triclosan between the bulk medium and the surface of the spherical nanoparticles. ) is given by [21] :…”

“…Fulfilment of both conditions is not difficult for a sample containing the target analyte only, but in heterogeneous environmental samples containing binding components such as humic acids, nanoparticles and proteins, it becomes a challenge. Association of target molecules with different sample constituents generally leads to lowering of the concentration measured by SPME (if only the free form is accumulated) [1,6,7] and significant changes in the extraction kinetics (for example by labile complexes of the target that facilitate the diffusive transport [8] ). A recent study utilising confocal laser spectroscopy showed, however, that complexing silica nanoparticles do partition into the extracting solid phase, poly(dimethylsiloxane) (PDMS).…”

“…, molar mass computed as ,2 Â 10 6 g mol À1 [6] ), acetone, ethanol and liquid chromatography-mass spectrometry (LC-MS) grade methanol were obtained from Sigma-Aldrich (Zwijndrecht, the Netherlands). Glass fibres with a core diameter of 110 mm and a 100-mm PDMS film (volume 0.6667 mL cm À1 ) were obtained from Poly Micro Industries (Phoenix, AZ).…”

“…Such values of k ad and k des render the system dynamic on the time scale of SPME, implying that the bulk equilibrium between free and bound organic is maintained. Under conditions of the present SPME experiments, the ratio between the kinetic flux and the diffusive flux of the nanoparticle-bound TCS is computed to be ,1.4 Â 10 3 (for details on the computation, see Zielińska et al [6] ). Because this is much larger than unity, the triclosan-SiO 2 nanoparticle complex system will be fully labile in the process of transfer of triclosan molecules from the bulk medium to the SPME surface.…”

Lability of nanoparticulate metal complexes in electrochemical speciation analysis

“…Non-equilibrium speciation techniques, such as various electrochemical methods [4], diffusive gradients in thin film (DGT) [5], and dynamic solid phase microextraction (SPME) [6], provide a measure of the fluxes and reactivities of species [7][8][9]. The pertaining knowledge is operationally formulated in terms of the lability of the complex species, i.e.…”