Vapours, detection

For vapour detection there are three aspects that are modelled sensitivity, response time, and regeneration. The sensitivity determines at which concentration level the detector will respond. The theoretical detector output (alarm or no alarm) is calculated by comparing the input data (concentration, relative humidity) with empirical detector display outputs, obtained during controlled exposure laboratory experiments. The response time determines how long it takes before the detector actually shows the response and it depends on the concentration level. The regeneration time determines how long it takes, after a positive detection, before the detector can do a new measurement. 

Giordano, M. Russo, M. Cusano, A. Mensitieri, G., An high sensitivity optical sensor for chloroform vapours detection based on nanometric film of 5 form syndiotactic polystyrene, Sens. Actuators B 2005, 107, 140 147... 

Phosphorus type - - Alkali metal thermionic Caesium bromide vapour detection - [403]... 

Traces of explosives are commonly present in very low levels in samples that are analysed, so it is important to take sensitivity into account when designing detectors for explosive detection. As a rough rule of thumb , Nambayah and Quickenden [38] reported that a method suitable for direct explosive vapour detection should be able to detect explosive concentrations at less than 1 ng/L. They made an exhaustive study of the lowest experimental detection limits achieved with various analytical techniques reported in the literature on traces of explosive, and they informed that headspace GC-electron capture detector (ECD) followed by immunosensor techniques achieves the lowest detection limits (from 0.07 to 20 ng/L). 

Notes. The method removes the sulphide interference from the cold-vapour mercury signal. Concentrations of sulphide as high as 20mgr1 S2-(as Na2S) do not interfere with the recovery of inorganic mercury added to distilled water. However, the oxidation technique suffers from chloride interference. If chloride is present in the sample it utilises oxidant and is oxidised to chlorine which interferes with the cold-vapour detection by absorbing radiation at the same wavelength as mercury. 

The main use of TLC in analysis of amoxicillin and its formulated products is as an identity test. A major study [105] using silica gel and silanised silica gel plates with thirty five different mobile phases and iodine vapour detection produced a system, on silanised plates with ammonium acetate/acetone mobile phase, in which amoxicillin was separated from all the other penicillins studied. A slightly modified version of this system was subsequently introduced into the European and British Pharmacopoeia monographs for amoxicillin trihydrate and sodium salt [2]. The British [57,58] and US [9] Pharmacopoeias specify other TLC systems for identification of amoxicillin in formulated products. Simple TLC methods have been developed for identification of several compounds on the WHO essential drugs list, to help combat counterfeiting [106]. For amoxicillin, systems using ethyl acetate/acetic acid/water or acetone/toluene/acetic acid/water with silica gel plates were recommended. 

Amoxicillin penicilloic acid, V, was detected in human urine by TLC with iodine vapour detection and identified by co-chromatography with the product of alkaline and (3-lactamase hydrolysis [146]. The identification was confirmed by other workers using TLC and HPLC [147-149]. 

As a result of their low vapour pressures, explosives detection in realtime using sniffer technologies presents significant detection challenges. A breakthrough that has enabled a paradigm shift toward explosive vapour detection came in 1998 when our group developed a sensory material with extraordinary sensitivity to TNT and DNT (trinitrotoluene and di-... 

Electronic noses are vapour detection systems that mimic key principles of biological olfaction [1]. The functioning principles of biological, olfactory systems do not rely upon selective interactions with specific analytes, but rather on cross-reactive receptors [2]. The receptors respond to many odours, generating unique response patterns, which serve as fingerprints for each odour. 

Figure l.A Common electrochemical sensor setup. B Setup for TNT vapour detection... 

Preliminary results are presented for the use of cyclic voltammetiy as a method for pattern recognition. The current at eight potentials of a cyclic voltammgramm was analyzed and these values served as a simulation of eight amperometric sensors. It is shown that on the basis of this procedure, different explosives and apple juices are easily distinguished by the use of one electrode alone These results clearly show that cyclic voltammetry could easily be used for a so called electronic tongue. In the future it is planned to use cyclic voltammetry as a method in combination with different sensor methods and also for the vapour detection. 

EXPLOSIVE VAPOUR DETECTION USING MICROMECHANICAL SENSORS... 

Keywords Cantilever sensors, explosive vapour detection, resonance frequency,... 

T. Thundat, G.Y. Chen, R.J. Warmack, D.P. Allison and E.A. Wachter, Vapour detection using resonating microcantilevers, Anal)dical Chemistry, 67 (1995) 519-521. 

A discussion followed regarding the question whether electronic noses will he able to complement or replace existing technologies for trace and vapour detection of explosives... 

Explosive vapour detection using micromechanical sensors 249... 

Multiphoton ionization spectroscopy has been reviewed in two recent articles. An apparatus has been described for constant intensity multiphoton ionization spectroscopy. A sensitive molecular vapour detection system utilizing resonance-enhanced two-photon ionization has been used to monitor naphthalene to a limit of 5 x 10 molecules cm Excitation was achieved... 

Rella R., Spadavecchia J., Ciccarella G., Siciliano P., Vasapollo G., and Valli L., Optochemical vapour detection using spin coated thin films of metal substituted phtha-locyanines. Sens. Actuators B, 89, 86-91, 2003. 

Penza, M., Antolini,F. and Vittori-Antisari, M. (2005), Carbon nanotubes-based surface acoustic waves oscillating sensor for vapour detection Thin Solid Films, 472,246-52. 

J. T. English, B. A. Deore, M. S. Freund, Biogenic amine vapour detection using poly(anilineboronic acid) films, Sensors and Actuators B Chemical 2006,115, 666. 

With this equipment many small molecules are detectable (Table 1). Some of them are particularly important in fruit analysis. Water vapour detection allows one to monitor respiration processes ethanol and especially acetaldehyde measurements permit one to follow the onset of fermentation (Bijnen 1995) ethane is taken as an indicator of cell membrane damage. It should be noted that periodic release of methane by cockroaches is investigated in detail with this setup (Bijnen 1995). 

Hosseini SH, Oskooei SHA, Entezami AA (2005) Toxic gas and vapour detection by polyanUine gas sensors. Iran Polym J 14(4) 333-344... 

Snow ES, Perkins FK, Robinson JA (2006) Chemical vapour detection using single walled carbon nanotubes. Chem Soc Rev 35 790-798... 

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