Journal des techniques analytiques et bioanalytiques

Abstrait

Development of a Thin-Film Microextraction Device based on ZSM-5/Tenax TA for VOC Detection in Liquid Samples

Shigemi Goda, Roman Selyanchyn, Takuma Nozoe, Hidetaka Matsui and Seung Woo Lee

The zeolite material ZSM-5 was combined with Tenax TA, a porous polymer adsorbent, to form a thin film microextraction (TFME) device that was used as a novel alternative tool for headspace (HS) volatile organic compound (VOC) extraction and preconcentration. The ZSM-5/Tenax TA film deposited on a cylindrical aluminium rod (AR) substrate exhibited superior properties for the adsorption and preconcentration of chloroform, hexane, cyclohexane, benzene, and toluene compared with those of a conventional Tenax TA film when applied in both the direct and HS extraction modes. The advantages of the fabricated device include its enhanced chromatographic performance and consequently lower detection limits for certain VOCs, the improved retention of compounds in the film (possibly enabling its application for both HS and direct extractions from aqueous solutions), the exceptional simplicity of its fabrication, and its robustness. The use of the film for HS extraction leads to increased application lifetime, film stability and shorter preparation times, because drying step is not necessary. Desorption of the adsorbed VOCs was achieved by heating in a conventional Curie point injector for less than 2 min.

It should be noted that the catalytic properties of the zeolite can be disadvantageous at high VOC concentrations (e.g., 100 μM); abundant background peaks as a result of a range of saturated and unsaturated hydrocarbons generated via catalytic degradation of adsorbed compounds at high temperature in the presence of ZSM-5 appear in the gas chromatograph. This effect is still visible at concentrations as low as 10 μM, but does not influence the measurement results. Thus, safe and accurate analyses are achievable at the liquid VOC concentrations in the submicromalar range, which is sufficient for a number of important analytical applications (e.g., detection of VOCs in waste water).