Detection airborne chemicals

When we smell something, we are detecting airborne chemicals volatile (meaning unstable, liable to disintegrate, or evaporate) molecules that are dispersed in the air. Objects that do not give off any sort of smell, like steel or stone, are nonvolatile solids that do not emit any free-floating molecules for the nose to detect. These airborne chemicals, also known as... 

As a species, humans are quite adept at detecting airborne chemicals, and just like with touch, we are capable of making very flne distinctions between different odors, or between different sets of odors. Our sensitivity to an odor will depend on the specific chemical involved. The term odor detection threshold is used to describe the minimum concentration of an airborne chemical that must exist for us to smell it. Thresholds for different chemicals are determined using a device known as an olfactometer. It is basically a device that can provide a quantitative answer to the question Exactly how badly does this thing stink ... 

Whereas the olfactory epithelium only detects airborne volatiles, Wysocki, Wellington and Beauchamp (1980) demonstrated that the VN organ detects involatile chemicals, which are actively pumped into it (vomeronasal pumping Meredith, Marques, O Connell and Stern, 1980). Although in vitro some volatiles are able... 

Recent developments in the field of sensing airborne chemicals using electrochemical sensors and sensor arrays are reviewed. Such systems detect, Identify, and quantify potential chemical hazards to protect the health and safety of workers and citizens. The application discussed In this review article Is single chemicals at part-per-million levels in air. The sensor system consists of an array of sensors used In four modes of operation, and the data are Interpreted by a computer algorithm. Pattern recognition techniques are being used to understand the information content of the arrays and to focus future experimental work. 

Solving these gas and vapor detection problems will require a variety of new sensors, sensor systems, and instruments. Field detection of airborne chemicals can be somewhat arbitrarily divided into three distinct situations. The first case is when a spill or leak results in a single compound occurring in air far in excess of its background concentration. The second case is when one or several trace constituent(s) occur in a complex background ("needle-in-the-haystack" problem). The third case is when a complete analysis is needed for all minor as well as major constituents of a complex mixture. The first case is the one specifically addressed by the approaches discussed in this review article. The second and... 

Amperometry can be used to detect and identify airborne chemicals, and devices based on this technology have existed for several years for measuring such gases as CO (1), NO ( 2), NO2 (2), (3),... 

In this manner, a nearly universal and very nonselective detector is created that is a compromise between widespread response and high selectivity. For example, the photoionization detector (PID) can detect part-per-billion levels of benzene but cannot detect methane. Conversely, the flame ionization detector (FID) can detect part-per-billion levels of methane but does not detect chlorinated compounds like CCl very effectively. By combining the filament and electrochemical sensor, all of these chemicals can be detected but only at part-per-million levels and above. Because most chemical vapors have toxic exposure limits above 1 ppm (a few such as hydrazines have limits below 1 ppm), this sensitivity is adequate for the initial applications. Several cases of electrochemical sensors being used at the sub-part-per-million level have been reported (3, 16). The filament and electrochemical sensor form the basic gas sensor required for detecting a wide variety of chemicals in air, but with little or no selectivity. The next step is to use an array of such sensors in a variety of ways (modes) to obtain the information required to perform the qualitative analysis of an unknown airborne chemical. 

Adsorption temperature, effect on TPD spectra of oxygen on Pd-doped tin(IV) oxide, 74,75 Airborne chemicals, detection and identification, 299-307 Alcohol sensors, general discussion, 333... 

Alcohol vapor, tin oxide sensor responses, 63,64-65f Algorithms, computer, detection and identification of airborne chemicals, 305-307... 

Protective wear and associated equipment are required to safeguard the worker. In the field where no detectable airborne pesticide emissions are present, but where the potential for skin contact is high, a hard hat with splash protector, safety glasses, chemically resistant outer clothing, gloves and boots with taped wrists and ankles, and inner surgical gloves would provide a conservative dress for field protection. The presence of detectable... 

The M18 detection kit and the M256A1 kit are mihtary items. The M18 is a colorimetric device for measuring the concentration of selected airborne chemicals. The Ml8 comes with detector tubes for cyanide, phosgene. Lewisite, sulfur mustard, and nerve agents GA, GB, GD, and VX. 

The sensitivity of cells to specific molecules is manifold. Such sensitivity includes the metabolic response of tissues to chemical messengers as well as the ability of lower organisms such as bacteria or protozoa to detect certain substances in the environment and its motion (chemotaxis). Among chemoreceptors we may mention gustatory (taste) receptors which detect dissolved ions and molecules, and olfactory (smell) receptors, which detect airborne molecules, and as a special case, synaptic receptors for chemical transmitters which propagate an electrical signal carried along an axon from one nerve cell end to another by way of chemical substances. 

D Agostino, P.A., et al. (1990) Capillary column gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry detection of chemical warfare agents in a complex airborne matrix. Journal of Chromatography A, 504, 259-268. 

Response characteristics of chemical detection and warning devices must be related to human physiological response characteristics, i.e., the dose or amount of toxic chemicals that would be ingested by an individual. Doses of materials ingested by people through exposure to airborne chemicals is usually reported in terms of a concentration (e.g., mg/m ) and the total time of the exposure (minutes) [1]. Most analytical instrument... 

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