Use of sorbents in air quality control systems

Abstract

Sorbent based methods have been successfully used in the collection of air samples to determine air quality. The complexity of the occurrence in air samples of several compounds in terms of composition (polar to non-polar compounds, very volatile to semi-volatile compounds) and abundance (below detection limit to over detector saturation limit) are topics that have to be taken into account when analytical methods are developed, especially in terms of sorbent choosing. An important amount of compounds found in air (eg. volatile organic compounds (VOC), volatile sulphur compounds (VSC) and polycyclic aromatic hydrocarbons (PAH)) generate odour problems, have associated R-phrases, are ozone precursors or have been declared carcinogens. The knowledge of their concentrations is very important to define air quality, not only in terms of odour nuisance but also in terms of toxicity. Therefore, emission and immission controls are important in air quality determination, both outdoors and indoors. Activated charcoal, Tenax TA, XAD-2, Carbotrap, Carbopack, Carbosieve and Carboxen 569 are found among the different types of sorbents available. They have variable selectivity towards the different types of compounds present in air. Hence, a good combination of different sorbents may allow the determination of a wide range of compounds in air samples. The idoneity, the hydrophobicity and the mesh size of the adsorbent particles together with the air flow, the air volume sampled, the ambient temperature and humidity would determine the adsorption efficiency of a compound. Several techniques are available for desorbing the compounds adsorbed, being the most relevant the ones based on thermal desorption and solvent extractions. When developing an analytical methodology, several quality criteria have to be taken into account focusing in the selectivity, sensitivity, linearity, precision, breakthrough and accuracy of the method. Comparatives between different types of sorbents (Tenax TA, self-made multi-bed tubes (Carbotrap, Carbopack X and Carboxen-569) and Radiello) arè done to determine the most reliable sorbent for the determination of concrete compounds present both in urban, rural and indoor air.