Odors concentration

Cross-country gas pipelines generally must odorize the normally odorless, colorless, and tasteless gas ia urban and suburban areas, as is required of gas distribution companies. Organosulfur compounds, such as mercaptans, are usually used for this purpose, and code requires that the odor must be strong enough for someone with a normal sense of smell to detect a gas leak iato air at one-fifth the lower explosive limit of gas—air mixtures. The latter is about 5%, so the odorant concentration should be about 1%, but most companies odorize more heavily than this as a safety precaution. 

Decipol A unit derived in an attempt to quantify odor concentration by the perception of odor. 

The threshold odor concentration of amines in air is typically 10 to 40 ppb. These levels are considerable less than any regulatory limit but offer potential for triggering complaints in laundries, kitchens, and sterilizing equipment rooms. 

T. Shimokawatoko, K. Sumida, and H. Ueda. Method and apparatus for measuring odorant concentration and oderant adding system. Patent US 5844124, 1998. 

A laboratory where the measurement takes place must be free from odor and is typically air-conditioned with air filtration. The odor sample is placed in an olfactometer that basically is a device for dilution of the sample. Typically, the meter has two outlet ports diluted odorous air flows from one, and clean odor-free air flows from the other. In dynamic olfactometry, panel members assess the two ports of the olfactometer. The assessors indicate from which of the ports the diluted sample is flowing. The measurement starts with a dilution that is large enough to make the odor concentration beyond the panelists threshold. This concentration is normally increased by a factor of two in each successive presentation. Only when the correct port is chosen and the assessor is certain that the choice is correct and not just a guess, is the response considered a true value. 

In the CEN procedure, the European odor unit per cubic meter, ou m-3 is used. The odor concentration at the detection threshold is defined as equal to 1 ou m-3. 

Buettner, A. (2002). Influence of human saliva on odorant concentrations 2. J. Agric Food Chem. 50,7105-7110... 

One method of controlling response perseveration and other anticipation factors is to use a forced choice response indication based on two or more response categories. In the measurement of odors the panelist has to report the temporal position of positive stimuli in a series of random blanks. If the concentration is below the threshold, the test subjects will guess. As the odorant concentration will increase, the relative cumulative frequency for identification of the correct sample will be greater. In order to determine the relative odor recognition a correction must be made. 

The characteristic curve of the odor threshold is used. The relative cumulative frequency of positive answers is calculated for each odorant concentration and graphically plotted, while for odor concentration a logarithmic scale is used. The odor threshold can be obtained from the resulting curve as the 50-percentile and so can the associated 16- and 84-percentiles. 

Pale amber liquid with a slight phenolic, floral, or musty-type odor. At 40 °C, the average and lowest odor concentrations detected were 0.36 and 0.088 pg/L, respectively. At 25 °C, the average taste threshold concentration and the lowest concentration at which a taste was detected were 0.97 and 0.94 pg/L, respectively (Young et al., 1996). 

Beyond that, the sense of olfaction does not depend on the concentration of the odorant concentration invariance. If you are exposed to jasmine at very low concentration, it smells like jasmine if the concentration is significantly raised, it still smells like jasmine. Perhaps more to the point is the concentration invariance of complex aromas such as that of coffee. The brain forms a single perception from complex inputs, regardless of the intensity of the signal. Olfaction has this property in common with taste. 

Aesthetic quality threshold odor concentration 1 - g/L WHO 1984a... 

For butadiene wastewaters with initial odor concentration of 1200, it was reduced to 100 and 250 after bubble aeration and spray aeration, respectively. For styrene wastewaters with initial odor concentration of 1000, it was reduced to 50 with bubble aeration and there was no odor reduction using spray aeration [6]. Sulfonation treatment for butadiene wastewater with initial odor... 

The biologically significant active space where the odor concentration is above threshold is shaped like an overturned boat (Fig. 1.4). (If the molecules were able to spread in all directions, as from an elevated odor source, the active space would assume the shape of a cylinder with pointed ends.)... 

The Gaussian plume model estimates the average pheromone flux by multiplying the measured odor concentration by mean wind speed, using the following formula (Elkinton etal, 1984). Everything is the same as in the Sutton model, except that ay and az, respectively, replace the terms Cy and Cz of the Sutton model. Dispersion coefficients are determined for each experiment separately. 

In general, perceived odor intensity is a power function of the odor concentration. The exponent is below 1, meaning that boosting the perceived intensity requires increasingly more odor production. As odor production becomes more and more costly, fine-tuning of chemoreception (instead of odor production) becomes the more attractive alternative evolutionarily. 

Beaman, A. L. (1988). A novel approach to estimating the odor concentration distribution in the community. Atmospheric Environment 22,561-568. 

The highest OAVs were found for 4-hydroxy-2,5-dimethyl-3(2H)-fura-none, followed by ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, methyl 2-methylbutanoate and ( ,Z)-l,3,5-undecatriene. It is assumed that these odorants contribute strongly to the aroma of pineapples [50]. However, FD factors and OAVs are functions of the odorants concentrations in the extract, and are not psychophysical measures for perceived odour intensity [71,72]. To take this criticism into account, aroma models are prepared on the basis of the results of the quantitative analysis (reviewed in [9]) and in addition omission experiments are performed [9]. 

Odorant Concentration (pg/kg) Threshold (pg/kg water) Odour activity value ... 

All distillates were saturated with sodium chloride and extracted with diethyl ether. The ether extracts were dried over anhydrous sodium sulfate and then concentrated by careful distillation to the minimum practical volume (about 1 ml.). The yields of the resulting odor concentrates (on an ether-free basis) were estimated by gas chromatography. 

Total yields of odor concentrates obtained from concurrently and non-concurrently processed, freshly irradiated enzyme-inactivated beef and from stored (6 months) irradiated beef are summarized in Table III. The de-... 

The odor concentrates were separated by temperature-programmed gas chromatography on a 20% Carbowax 20M column. Typical chromatograms obtained from the distillate—i.e., the odor concentrate isolated... 

Infrared spectra of individual fractions were determined by means of a Beckman IR-5 spectrophotometer equipped with a 5 X KBr lens-type beam condenser. Infrared spectra of selected reference compounds were obtained from samples which had been purified by chromatography. On the basis of identity of infrared spectra and retention data with those of authentic reference compounds, most of the peaks shown in Figures 1 and 2 were identified (15,16). To obtain information about minor components not detectable in the infrared spectra, mass spectra were obtained as components of an irradiated odor concentrate were eluted from a 10-foot, J/g-inch 5% Carbowax 20M column programmed from 20° to 160°C. at 1° per minute. These spectra were obtained on a modified model 14 Bendix Time-of-Flight mass spectrometer. Electron energy was set at 70 e.v., and spectra were scanned from m/e 14-200 in 6 seconds. 

Table IV. Average Composition of Total Odor Concentrates from Nonirradiated and Irradiated Beef...

Based on the method of internal normalization of peak areas, the percentage composition (less the diethyl ether solvent shown as the initial large component in Figures 1 and 2) of odor concentrates was estimated. The average composition of samples of odor isolates from individual preparations as well as from several different preparations of the same type—i.e., concurrent or noncurrent—was determined on the basis of all preparations which could be compared on a fair analytical basis (same gas chromatographic detector, column, and conditions). These results were then combined (traps plus distillate) to provide the rough estimations shown in Table IV. These data represent the best estimation of the composition of the total volatile odor concentrates from each processing method studied. 

---