Investigation of the perceived air quality with an electrochemical sensor and an electronic nose

Electronic noses are instrumental apparatus based on the use of a chemical sensor array in which each sensor is characterised by a broad chemical selectivity. This feature is the key property on which electronic noses found their working principle. In this paper an electronic nose based on eight quartz microbalances coated by films of metalloporphyrins films deposited by spray casting. The resonance frequency variation of the quartz is proportional, to the total mass of the absorbed molecules, namely through their molecular mass, to the number of absorbed molecules and then to the concentration in the vapour phase. The other device used in this investigation is an electrochemical sensor based on transport or permeation of a gas to the surface of a gas permeable (microporous) PTFE membrane; the dissolution of gas into an internal electrolyte solution, which is the working solution (flow rate: 10-6÷10-4 kg s-1), varies the pH of the latter, producing reaction/dissociation of the gas in the electrolyte. As a signal an electromotive force across the electrodes is obtained, which is proportional to the analytes present in the gas phase. In order to verify the application of the two sensors in the classification, discrimination and recognition of chemical patterns occurring in different kind of samples, in this paper a comparison of the two sensors concerning the detection of small quantities of chemicals have been carried out