Vapours

About: Vapours is a research topic. Over the lifetime, 1153 publications have been published within this topic receiving 15022 citations.

Chemiresistive sensors of electrically conducting poly(2,5-thienylene vinylene) and copolymers: their responses to nine organic vapours

Abstract: An apparatus and a method are described to test the sensing capacities, in the context of an electronic nose, of conductimetric sensors for organic vapours. Such a sensor was constructed using iodine doped poly(2,5-thienylene vinylene) (PTV) and tested in detecting nine ‘representative’ vapours. Responses after 1 min exposure are high and mostly linear with respect to concentrations. Recoveries, however, using 4 min of clean air, are only partial. Yet, responses and recoveries are reproducible and characteristic for a particular vapour. Partial methanol elimination from the methoxy-precursor polymer of PTV leads to new sensing materials with different selectivities. Also discussed are: (i) influence of the humidity of the carrier gas (air), (ii) possible causes of observed baseline-drift and (iii) possibilities of regeneration of the materials after prolonged use. It is concluded that PTV and derivatives show promise as active materials in sensor arrays.

Strategies for the simultaneous collection of vapours and aerosols with emphasis on isocyanate sampling.

Abstract: Workplace air frequently contains hazardous substances that may be present as vapours or as aerosols with a wide range of particle sizes. Depending upon a chemical species' volatility and use, it may be present in significant amounts in both the vapour and particulate phases. Unfortunately, the mechanisms by which vapours and particles are removed from an air stream during pumped sampling are substantially different. Collection of vapour molecules relies on their diffusion to a surface during their residence time in a sampler. Once in contact with a surface, vapour molecules are trapped either by adsorption onto a solid surface, absorption by a liquid, or by reaction with the medium or chemicals in the medium. Aerosol particles are most frequently collected by filtration or inertial impaction. However, if it is necessary to collect both phases simultaneously, a sampler with two stages is generally required. The exact nature of the sampler depends upon the size of the aerosol particles and the physical and chemical characteristics of the species of interest. A number of recent projects undertaken by researchers at the National Institute for Occupational Safety and Health have dealt with development of sampling and analytical methods for compounds present in workplace air as both vapour and aerosol particles. One strategy invoked in several instances consisted of a filter for particle collection followed by an appropriate second stage for vapour collection. For organophosphorus pesticides, the second stage was a sorbent tube. For gaseous hydrogen fluoride, it was an alkaline-impregnated back-up pad. For formaldehyde, the second stage was an impinger containing an aqueous solution of sodium hydrogensulfite.(ABSTRACT TRUNCATED AT 250 WORDS)

Cavitands as selective materials for QMB sensors for nitrobenzene and other aromatic vapours

Abstract: The sensitivity of vase-like cavitands to nitrobenzene and other organic and inorganic vapours has been investigated by using the technique of the quartz microbalance (QMB) in order to determine the variation of the mass adsorbed. Cavitands at room temperature showed a high selectivity to nitrobenzene with respect to benzene and other organic vapours like toluene, fluorobenzene and carbon tetrachloride. This material is insensitive towards other vapours, present in a concentration of 1000 ppm, like H 2 , CO, SO 2 , H 2 S, NO and NO 2 , an it is also insensitive to relative humidities up to 90%. The X-ray structure analysis of the host—guest complex with the fluorobenzene is also described.

Poly(alkoxy-bithiophenes) sensors for organic vapours

Abstract: This work reports electrical resistance measurements and on line UV–Vis–NIR spectra for sensors, fabricated from poly(3,3′-dipentoxy-2,2′-bithiophene) (I) or poly[3,3′-2-(2-ethoxy)ethoxy-2,2′-bithiophene] (II) doped with FeCl 3 , Fe(ClO 4 ) 3 , or CuCl 2 , and tested against vapours of o -xylene, n -butanol, benzene, methanol, n -heptane, and 3-pentanone over a 50–66,444 ppm (v/v) concentration range in argon. Each sensor was exposed repeatedly and randomly to the test vapours in a wide concentration range over a maximum of 41 times and 25 days. Neat argon sweeping was performed between test vapour injections to recover base line conditions and test sensor reversibility. The percentage changes of electrical resistance, relative to the value measured before exposure, and of the sensor absorbance at 880–1400 nm, both varied linearly according to the concentration used. The sensitivities α were calculated from the linear regression analysis of 80 sets of Δ R , C values for a total of about 400 measurements, in order to assess the influence of several parameters, i.e. the chemical nature of the sensor, the fabrication, the exposure time to the test vapour, and the ageing in air. The data analysis demonstrated that sensitivity depends on the chemical nature of both the sensor and the test vapour and on the length of exposure. Data collected with a 90 s exposure gave the narrower range of standard deviation values, amounting to 14% of the calculated α value in the worst case, whereas α values over the range of sensor and test vapour combinations varied from 3.4×10 −5 for I doped FeCl 3 versus MeOH to 231×10 −5 for I doped with Fe(ClO 4 ) 3 versus o -xylene. A significant base line drift was observed at the longest working time, but it was not proven to affect the sensitivity of the sensor. The concomitant changes of the sensors and of the electronic spectra offer intriguing scope to further investigate the nature of the sensor–test vapour interaction.