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Abstract: A highly sensitive sensing paper that uses the reaction of ozone with azo dye orange I has been developed for ambient ozone monitoring. This reaction results in reaction products, without absorption in visible region, on paper that can be determined by measuring the reflectance spectrum of the paper. The combination of a cellulose sheet, a humectant (glycerol), an alkali (sodium hydroxide) and orange I is needed to achieve a sensitive sensing paper. We found that the pH of the immersion solution used for preparing the sensing paper had a strong influence on the paper''s responsivity to ozone. Ozone detection papers that were made using acidic or neutral immersed solutions were not faded by ozone exposure, whereas those made using a strong alkaline immersion solution were faded by ozone exposure and the color of the paper faded completely at an ozone exposure of about 400ppb×h. We considered an orange I reaction site for ozone using UV–vis spectrum measurements and molecular orbital calculation by comparing experimental results for both orange I and its isomer orange II. It was estimated that the hydrazone form of orange I in alkaline condition would be sensitive to ozone. [Copyright &y& Elsevier]

Abstract: The paper critically reviews the state of the art in the field of experimental techniques possible to be applied to the study of conductometric gas sensors based on semiconducting metal oxides. The used assessment criteria are subordinated to the proposed R&D approach, which focuses on the study, and subsequent modelling, of sensors’ performance in realistic operation conditions by means of a combination of phenomenological and spectroscopic techniques. With this viewpoint, the paper presents both the to-date achievements and shortcomings of different experimental techniques, describes – by using selected examples – how the proposed approach can be used and proposes a set of objectives for the near future. [Copyright &y& Elsevier]