Odors measurable characteristics

Psychophysics explores the relationships between measurable characteristics of stimuli and their perception. In the case of odor as a stimulus, the only two quantitatively measurable aspects, at our current state of knowledge, are concentrations and the composition of mixtures. Hence the psychophysics of odor deals with measuring the perception of given odorants at different concentrations and with the perception of mixtures. 

Four characteristics of odor are subject to measurement by sensory techniques intensity, detectability, character (quality), and hedonic tone (pleasantness-unpleasantness) (16). Odor intensity is the magnitude of the perceived sensation and is classified by a descriptive scale, e.g., faint-moderate-strong, or a 1-10 numerical scale. The detectability of an odor or threshold limit is not an absolute level but depends on how the odorant is present, e.g., alone or in a mixture. Odor character or qualit) is the characteristic which permits its description or classification by comparison to other odors, i.e., sweet or sour, or like that of a skunk. The last characteristic is the hedonic type, which refers to the acceptability of an odorant. For the infrequent visitor, the smell of a large commercial bread bakery may be of high intensity but pleasant. For the nearby resident, the smell may be less acceptable. 

Sensitive Receptor Indicator a measurable physical, chemical, biological, or social (e.g., odor) characteristic of a sensitive receptor. For example, for the sensitive receptor. Crater Lake, water clarity is a sensitive receptor indicator. 

In addition to sampling in a sewer followed by analysis of specific components or use of a sample for further laboratory or pilot-scale experiments, a number of direct or indirect measurements must typically be performed in the sewer itself. Important measurements related to sewer process studies are DO, reaeration, biofilm characteristics and odor. 

Elemental composition H 5.92%, S 94.08. Hydrogen sulfide may be distinguished by its characteristic odor. The gas turns a paper soaked in lead acetate solution black. Many infrared sensors are commercially available for in-situ measurements of H2S. It may be monitored semiquantitatively by Draeger tubes. It also may be analyzed by GC following trapping over molecular sieves and thermal desorption. Either a flame photometric detector or a sulfur chemiluminescence detector may be used for GC analysis. It may be separated on a capillary column such as Carboxen 1006 PLOT or SPB-1 SULFUR (Supelco Catalog 1999 Supelco Inc., BeUefonte, PA). 

Nitrogen dioxide can be identified by color, odor, and physical properties. It is dissolved in warm water and converted to nitric acid. The latter may be measured by acid-base titration or from analysis of nitrate ion by nitrate ion-specific electrode or by ion chromatography. Alternatively, nitrogen dioxide may be passed over heated charcoal to produce nitrogen and carbon dioxide that may be analysed by GC-TCD or GC/MS (See Nitrogen, Analysis). The characteristic masses for N2 and CO2 formed for their identification are 28 and 44, respectively. 

The acceptance criteria may also specify limits on microbial counts, endotoxin, particulate matter, and other parameters appropriate or significant for the particular product. The author remembers one protocol that specified the absence of a characteristic odor that was indicative of a certain residue and was a sensitive yet simple measure of whether or not the equipment was adequately cleaned. 

Ammonia is readily detectable in air in the range of a few parts per million by its characteristic odor and alkaline reaction. Specific indicators, such as Nessler s reagent (Hgk in KOH), can detect ammonia in a concentration of 1 ppm. For the quantitative determination of ammonia in air, synthesis gas and aqueous solutions, these methods can be used74 Acidimetry and Volumetric Analysis By Absorption, Gas Chromatography, Infrared Absorption, Thermal Conductivity Measurement, Electrical Conductivity Measurement, Measurement of Heat of Neutralization, and Density Measurement (for aqueous ammonia). 

Odor affects the drinkability of water. It is measured by the threshold odor number (TON). This is the dilution factor necessary before the odor is perceptible. A TON of 1 indicates that the water has characteristics comparable to odor-free water. 

Single-component adsorption equilibria on activated carbon of the n-alkanes Q-C4 and of the odorant tert-butyl mercaptan were measured at the operating conditions expected in a large-scale facility for adsorbed natural gas (ANG) storage. The experimental data were correlated successfully with the Adsorption Potential theory and collapsed into a single temperature-independent characteristic curve. The obtained isotherm model should prove to be very useful for predicting the adsorption capacity of an ANG storage tank and to size and optimize the operation of a carbon-based filter for ANG applications. 

Propoxyphene hydrochloride is a white, crystalline powder with no noticeable odor and a bitter taste. The melting range is 162.5°C -168.5°C. The specific rotation for a one perj cent solution should be between +52° and +57° Propoxyphene hydrochloride has a unique characteristic, in that the specific rotation value has an apparent dependency upon the concentrg-tion of the solution being measured. An [or] D value of +59.8° is given in literature2 (for a 0.6 percent solution). 

Unfortunately, commercially available DMSO has a characteristically objectionable odor which is caused by low-level impurities, considerably lower than 1%, largely dimethyl sulfide (DMS) but also a small number of other sulfur-containing compounds. These compounds have an effect on taste as well as smell. They are particularly measurable by UV absorption at 275 mp,. Technical Grade DMSO (pharmaceutically objectionable odor) has a UV275 > 0.25. Lowering UV275 to <0.1 makes DMSO essentially odorless. 

The background of the evaluation of air quahty using human subjects and the currently available methodologies are presented as well as the sources and chemical compounds measured. Section 2 focuses on the perception mechanisms for odour and irritants. Techniques to evaluate air quahty with human panels are described and discussed in Sect. 3. And in Sect. 4 some of the indoor air pollutants are discussed with respect to their odor characteristics and their possible indoor-related sources using the results of several European projects. 

Gas chromatography-olfactometry (GCO) has been used extensively for the identification of characteristic aroma conq)onents of foods (9,10). Aroma extract dilution analysis (AEDA) is a GCO technique in which serial dilutions (e.g. 1 3) of an aroma extract are evaluated by GCO. In AEDA, the highest dilution at which an odorant is last detected during GCO, so-called flavor dilution (FD) factor, is used as a measure of its odor potency (P). One potential drawback to AEDA is that the technique is limited to the analysis of components of intermediate and low volatility. To overcome this limitation, AEDA results have been con5>lemented by results of GCO of decreasing dynamic headspace (DHS) and decreasing static headspace (GCO-H) san5)les (70,77)... 

The concentration divided by the odor threshold value, C/T is called the aroma value (22). Odorants with high aroma values are important contributors to the characteristic flavors. In general, the estimated feel of the stimulus is logarithmically proportional to the objectively measured strength of the stimulus... 

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