Sensors and Actuators B 105 (2005) 400–406 Selectivity enhancement of metal oxide gas sensors using a micromachined gas chromatographic column S. Zampolli a,∗ , I. Elmi a , J. St ¨ urmann b , S. Nicoletti a , L. Dori a , G.C. Cardinali a a CNR – IMM Sezione di Bologna, Via P. Gobetti 101, 40129 Bologna, Italy b IMSAS, University of Bremen, Otto-Hahn-Allee 28359, Germany Received 27 February 2004; received in revised form 23 June 2004; accepted 25 June 2004 Available online 3 August 2004 Abstract Indoor air quality monitoring applications require both high sensitivity and selectivity, which are difficult to reach with solid state gas sensors. While for some gas species like, e.g. CO and NO 2 , the use of optimized operating conditions allows to reach the necessary selectivity, the dis- crimination between single volatile organic compounds (VOC) is generally not possible with stand-alone arrays of gas sensors. This limitation represents a major drawback, since not all indoor VOC are equally harmful for the health of the human beings living in the polluted environment. For this reason, a highly selective hybrid microsystem based on a gas chromatographic-like (GC) approach is proposed. In this miniaturized gas chromatographic system a solid state gas sensor is used as detector, together with a Silicon micromachined packed GC column, a zero grade air unit, a commercial minipump and a minivalve. With this prototype, Benzene, Toluene and m-Xylene eluted in synthetic or real indoor air were reliably detected and measured at concentrations as low as 5 ppb. The use of chromatographic units together with solid state gas sensors both integrated in silicon allows to develop low-cost, handheld portable devices having exceptional selectivity and reproducibility. Possible applications which could benefit of these performances include security control, air quality monitoring as well as food quality control. © 2004 Elsevier B.V. All rights reserved. Keywords: Indoor air quality; Gas sensors; Electronic Nose; Packed gas chromatography 1. Introduction Long-term occupancy in confined living spaces with poor ventilation, like office buildings or homes and apartments, has been identified as the main responsible of a new class of dis- eases related with the presence of physical, biological and/or chemical contaminants and identified as Building-Related Ill- nesses (BRI) and Sick Building Syndromes (SBS). Typical indoor contaminants include by-products of the combustion (NO 2 , SO 2 , CO, etc.), cigarette smoke, particu- late matter, mineral fibers and a number of volatile organic compounds [1,2]. In spite of the very low concentrations, some of these compounds like, e.g. benzene and formalde- hyde are proved to be carcinogenic. Therefore, the monitoring of indoor air quality is of paramount importance to keep safe and healthy conditions. ∗ Corresponding author. Tel.: +39 051 639 9109; fax: +39 051 639 9216. E-mail address: zampolli@bo.imm.cnr.it (S. Zampolli). In buildings equipped with forced ventilation, the pol- lutants are diluted by Heating Ventilation Air Condition- ing (HVAC) systems, which are generally operated on the basis of fixed duty cycles. A preventive increase of the ventilation doesn’t necessarily improve the indoor air quality, since in many cities “fresh” outdoor air may be highly polluted, on the other hand it may boost up the overall energy consumption, especially when the tempera- ture gap between indoor and outdoor air is non-negligible [3]. In literature, the implementation of demand-controlled ventilation mainly relies on the quantification of CO 2 , used as a tracer of human occupancy in confined living spaces or as surrogate of inhabitant generated pollution. This ap- proach is inadequate to monitor IAQ, since there are many toxic compounds, which are released by building materials and furnishings. Furthermore, each compound has a different impact on human health and it is important to monitor their concentrations individually. 0925-4005/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2004.06.036