Organic vapor detectors

Monitoring equipment appropriate to the hazards present shall be available. This may include organic vapor detectors of various types, combustible gas detectors, oxygen detectors, detector tubes and pumps, and specialized detectors such as mercury detectors. 

Harden T.C. Imeson, Detection and Identification of Trace Quantities of Organic Vapors in the Atmosphere by Ion Cluster Mass Spectrometry and the Ionization Detector System ,... 

Before a well is sampled, as a health and safety measure, we may record organic vapor contents in the wellhead with a field photoionization detector (PID). Chemical odors emanating from the well may overpower the sampler and warrant the use of appropriate PPE. 

An electrochemical flow detector, based on four working electrodes coated with different permselective film types, for use in flow-injection measurements of multiple nitroaromatic explosives was recently developed [18]. The resulting array response (Fig. 4) offers unique fingerprints of such explosive compounds. Electrochemical devices are extremely attractive for designing such e-nose-type multi-electrode arrays that combine several partially selective electrodes and lead to a distinct response pattern (signature) for mixtures of organic vapors without prior separation [2],... 

Barsky JB, Hee SSQ, Clark CS. 1985. An evaluation of the response of some portable, direct-reading 10.2 electron volt and 11.8 electron volt photoionization detectors and a flame ionization gas chromatograph for organic vapors in high humidity atmospheres. Am Ind Hyg Assoc J 46 9-14. 

Currently acceptance standards applied to hydrogen sensors follow the existing UL 2075 Standard for Safety Gas and Vapor Detectors and Sensors and the relevant flatmnable gas standards in the US such as NFPA 52 and 55. The International Organization for Standardization (ISO) Technical... 

As the current increases due to the presence of organic vapor, the voltage drop across the linearizing resistance also increases and reduces the voltage across the electrode. For example if 1300 volts is applied to the detector and when a solute is eluted, the current increases to 10" amp, this will cause a 300 volt drop across the linearizing resistance of 3 x 10 and consequently reduce the voltage across the electrodes to 1000 volts. In this way the natural exponential response of the detector can be made sensibly linear. 

Hopkins, A.R., and N.S. Lewis. 2001. Detection and classification characteristics of arrays of carbon black/organic polymer composite chemiresistive vapor detectors for the nerve agent stimulant dimethyl-methylphosphonate and diisopropylmethylphosponate. Analytical Chemistry 73(5) 884-892. 

Ionization detectors measure variations in saturation current of a gas passing between two electrodes across which a constant voltage is applied. The variation in current is caused by ionized, organic vapors as they emerge from the column, and is amplified and recorded as with the thermal-conductivity detector. The organic vapors are ionized either by a source of... 

In previous sections, carbon materials serve either as sensing materials or as transducers. Many studies also use carbon-polymer composites, where carbon materials serve as both support and transducer. The polymer-coated FET discussed above is one example. Arrays of carbon black/organic polymer composite have also been demonstrated in many studies as chemiresistive vapor detectors... 

At the temperatures and pressures generally used in gas chromatography the common carrier gases employed behave as perfect insulators. In the absence of conduction by the gas molecules themselves, the increased conductivity due to the presence of very few charged species is easily measured, providing the low sample detection limits characteristic of ionization based detectors [259]. Examples of ionization detectors in current use include the flame ionization detector (FID), thermionic ionization detector (TID), photoionization detector (PID), the electron-capture detector (ECD), and the helium ionization detector (HID). Each detector employs a different method of ion production, but in all cases the quantitative basis of detector operation corresponds to the fluctuations of an ion current in the presence of organic vapors. 

A different detection unit is the solid-scintillator proportional counter [6]. It consists of a scintillator with ultraviolet emission in a multi wire chamber filled with an organic vapor. The organic molecules are ionized by the ultraviolet photons and the resulting photoelectrons are detected in the multi wire chamber. A popular molecule in this aspect is TMAE (tetrakis (dimethylamino) ethylene). Figure 9.4 presents the spectral sensitivities of the detectors mentioned. 

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