Thickness-shear-mode acoustic wave sensor for acetone vapour coated with C-ethylcalix[4]resorcinarene and C-H ••• π interactions as a molecular recognition mechanism

The frequency response characteristics for 21 organic vapours by piezoelectric thickness-shear-mode (TSM) acoustic wave sensors coated with four calixarenes have been investigated. The results reveal that C-ethylcalix[4]resorcinarene (CECRA) is the most efficient adsorptive material for acetone. The decreased frequency values of the TSM sensor are linearly correlated to the concentration of acetone vapour in the 0-2280 ppm range with the detection limit of 1.25 ppm when the coating mass of CECRA is 18.5 mug. The adsorption and desorption response kinetics have been examined in detail, and the polynomial curve equations for the different processes have been obtained by data fitting with the least square regression method. The proposed sensor exhibits good reversibility, reproducibility, and stability for the determination of acetone vapour. No significant interference is observed from organic hydrophobic molecules such as alkanes, halohydrocarbons and aromatic hydrocarbons. By comparison with the gas chromatography method, the proposed sensor can be used for the determination of acetone vapour in air with the recovery of 96.8-104.2%. X-ray single crystal structure analyses of three complexes formed between CECRA and acetone molecules suggest a recognition mechanism in which an acetone molecule is captured as a guest in the cavity of a CECRA host molecule through C-H . . . pi interactions between the methyl groups of acetone and the phenyl rings of CECRA. (C) 2001 Elsevier Science B.V. All rights reserved.