In-situ kinetic and thermodynamic study of 2,4-dichlorophenoxyacetic acid adsorption on molecularly imprinted polymer based solid-phase microextraction coatings

Abstract

Solid-phase microextraction (SPME) is attracting increasing interest due to being promising, new and green sample-preparation technique. Despite the vast research on the SPME, little is known about adsorption kinetics and thermodynamics of SPME coating, which plays the key role in the extraction. In this paper, a blade type SPME coating was prepared on glass slide, and 2,4-dichlorophenoxyacetic acid (2,4-D) adsorption on the coating were monitored by in-situ fiber-optic sensing. The effects of contact time, temperature (298-318 K) and initial concentration (20-150 mg/L) of 2,4-D on the adsorption properties of SPME coating were discussed. The results demonstrated that the pseudo-second-order model was most suitable for describing 2,4-D adsorption on the SPME coating. The thermodynamic parameters (ΔH, ΔS, ΔG) indicate that 2,4-D adsorption at low concentration by the SPME coating is exothermic and spontaneous process. Under the same conditions, the molecularly imprinted polymers (MIPs) coating have significantly higher adsorption capacity, and faster adsorption rate than the non-imprinted polymers (NIPs) SPME coating. This approach provides a tool for in-situ monitoring of adsorption kinetics and thermodynamics of SPME coating which requires fast measurement and small volume.