Identification by cryofocusing–gas chromatography–mass spectrometry of odorous cyclic acetals emitted from a polyester resin plant

A simple and inexpensive cryofocusing device was developed ad hoc in order to analyse at sub-ppb levels airborne organics, sampled by Tenax tubes and recovered by thermal desorption. By means of this device and of gas chromatography–mass spectrometry, the odorous compounds in the air around a polyester resin factory were identified as 2-ethyl-4-methyl-1,3-dioxolane (EMD), 5,5-dimethyl-1,3-dioxane (DMD), 2,5,5-trimethyl-1,3-dioxane (TMD), 2-ethyl-5,5-dimethyl-1,3-dioxane (EDMD) and 2-isopropyl-5,5- dimethyl-1,3-dioxane (IDMD). These compounds are produced during the synthesis of polyester resins by cyclic acetalization of vicinal diols under acid catalysis. Their structures were confirmed by laboratory syntheses. The Odour Index of these organics was evaluated by means of dynamic olfactometry, and the results were 22 100 for IDMD, 27 200 for DMD, 98 100 for EMD, 1 003 000 for TMD and 2 094 000 for EDMD. Their odour changes dramatically from a pleasant mint scent at higher concentrations to a very unpleasant smell at ppb level concentrations.