Cavitands as superior sorbents for benzene detection at trace levelElectronic supplementary information (ESI) available: synthetic procedures for the preparation of cavitands 2, 3; 29Si and 13C CP/MAS NMR spectra of MeCav and QxCav coated silica; desorption pattern of BTX observed for Tenax TA® at 50 °C; GC traces obtained from the desorption at 75 °C of the BTX mixture trapped on AXCav trap and Carbotrap 100®. See http://www.rsc.org/suppdata/nj/b2/b210942e/

Abstract

We present an innovative dynamic headspace-based approach to sampling of BTX using molecular receptors. For this purpose methylene-bridged (MeCav) and quinoxaline-bridged (QxCav) cavitands were silylated at the lower rim and grafted onto silica gel. In the case of QxCav, the resulting sorbent material selectively retains BTX at ppb levels in the adsorption phase and delivers a benzene-enriched fraction in the desorption phase. Under the same conditions, commercial sorbents like Carbotrap 100® and Tenax TA® proved to be unselective both in the uptake and in the release steps. The molecular origins of the observed selectivity were traced by theoretical calculations in the presence of multiple electrostatic and CH–π interactions, possible only in the case of QxCav–aromatic analyte complexes.