Smell detection

Figure 4.5. The NP composition of a typical plant extract (in this case, a citrus hybrid) as revealed by gas chromatographic analysis. The peaks on the upper trace represent the different chemicals detected by the instrument, with the peak area being a measure of the amount of any substance. Note that there are a few major NP peaks but even more very minor ones. The spikes pointing down on the lower trace are the odours detected by a human sniffer with their perceived odour name. Note the human detection of odour does not always correspond to the emergence of a major chemical peak. For example near the start of the analysis, the green or burning smell detected by the human does not correspond to any instrument detection so those chemicals are below the level of detection of the instrument. (Modified from the data of Morton M, Smoot JM, Mahattanatawee K, Grosser] and Rouseff RL, Citrus Research and Education Center, University of Florida.)...

A few comments on phenol Phenol is a monosubstituted aromatic hydrocarbon. In its pure state, it exists as a colorless or white solid. This pure compound is mixed with water and commercially sold as a liquid product. Phenol gives off a sweet, acrid smell detectable to most people at 40 ppb in air and at about 1-8 ppm in water (EPA, 2002). It evaporates more slowly than water and is moderately soluble in water. Phenol is also combustible. 

During drying the films take up ca. 10-20 wt% of oxygen (relative to the pure oil). The smell detected during drying is partly due to decomposition products of the binder that are formed during autoxidative polymerization. 

Chlorine is a greenish-yellow gas with a pungent bleach smell detectable in concentrations as low as 3.5 ppm. It is around 2.5 times denser than air and will accumulate in low-l5dng areas and enclosed spaces. 

When the fats are heated above 250"C they decompose with the production of acrolein, the intense smell of which is one of the best methods for detecting fats. The extraction of fats from tissues is most conveniently carried out by extraction with ether or some other solvent. 

I. Acrolein test. Heat 0-5 ml. with about i g. of finely powdered KHSO4. Acrolein, CH2 CH CHO, produced by dehydration of the glycerol, is readily detected by its characteristic and irritating odour smell cautiously). 

Place 5-2 g. (5 ml.) of anihne and 45 ml. of 10 per cent, aqueous sodium hydroxide solution in a wide-necked bottle (or, bF not available, a conical flask), and then add 8 -5 g. (7 ml.) of benzoyl chloride, stopper, and shake vigorously for 10-15 minutes. Heat is evolved in the reaction. The crude benzoyl derivative separates as a white powder. When the reaction is complete (t.e., when the odour of benzoyl chloride can no longer be detected smell cautiously), make sure that the reaction mixture is... 

METHOD 2 [89]--1M MDA or benzedrine and 1M benzaldehyde is dissolved in 95% ethanol (Everclear), stirred, the solvent removed by distillation then the oil vacuum distilled to give 95% yellow oil which is a Schiff base intermediate. 1M of this intermediate, plus 1M iodomethane, is sealed in a pipe bomb that s dumped in boiling water for 5 hours giving an orangy-red heavy oil. The oil is taken up in methanol, 1/8 its volume of dH20 is added and the solution refluxed for 30 minutes. Next, an equal volume of water is added and the whole solution boiled openly until no more odor of benzaldehyde is detected (smells like almond extract). The solution is acidified with acetic acid, washed with ether (discard ether), the MDMA or meth freebase liberated with NaOH and extracted with ether to afford a yield of 90% for meth and 65% for MDMA. That s not a bad conversion but what s with having to use benzaldehyde (a List chemical) Strike wonders if another aldehyde can substitute. 

Whatever the physiology of odor perception may be, the sense of smell is keener than that of taste (22). If flavors are classed into odors and tastes as is common practice in science, it can be calculated that there are probably more than 10 possible sensations of odor and only a few, perhaps five, sensations of taste (13,21,35—37). Just as a hereditary or genetic factor may cause taste variations between individuals toward phenylthiourea, a similar factor may be in operation with odor. The odor of the steroid androsterone, found in many foods and human sweat, may eflcit different responses from different individuals. Some are very sensitive to it and find it unpleasant. To others, who are less sensitive to it, it has a musk or sandalwood-like smell. Approximately 50% of the adults tested cannot detect any odor even at extremely high concentrations. It is befleved that this abiUty is genetically determined (38). 

Odors are measured by their intensity. The threshold value of one odor to another, however, can vary greatly. Detection threshold is the minimum physical intensity necessary for detection by a subject where the person is not required to identify the stimulus, but just detect the existence of the stimulus. Accordingly, threshold deterrninations are used to evaluate the effectiveness of different treatments and to estabflsh the level of odor control necessary to make a product acceptable (8). Concentration can also produce different odors for the same matenal. For example, indole (qv) in low concentrations has the smell of jasmine and a low threshold of perception. In high concentrations, it has a strong odor of feces and CX-naphthyl amine as well as a considerably higher threshold of perception. 

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. 

The odor threshold of carbon disulfide is about 1 ppm in air but varies widely depending on individual sensitivity and purity of the carbon disulfide. However, using the sense of smell to detect excessive concentrations of carbon disulfide is unreHable because of the frequent co-presence of hydrogen sulfide that dulls the olfactory sense. 

Detection. Many people can detect hydrogen cyanide by odor or taste sensation at the 1 ppm concentration in air, most at 5 ppm, but HCN does not have an offensive odor and a few people cannot smell it even at toxic levels. Anyone planning to work with hydrogen cyanide should be checked with a sniff test employing a known safe concentration. This test should be given periodically. Several chemical detection and warning methods can be employed. The most rehable are modem, electronic monitors based on electrolytes that react with hydrogen cyanide. 

Since the efficiency of this washing is dependent upon the degree of settling, the checkers recommend that washing with 50-mL batches of ether be continued until the smell of the alcohol is no longer detectable on a sample of the dry salts. 

In water containing sulfate, the use of the electrolysis protection process with low water consumption can sometimes result in the formation of small amounts of HjS, which is detectable by the smell. Sulfate reduction occurs through the action of bacteria in anaerobic areas (e.g., in the slurry zone of the tank). 

Cathodic protection with impressed current, aluminum or magnesium anodes does not lead to any promotion of germs in the water. There is also no multiplication of bacteria and fungi in the anode slime [32,33]. Unhygienic contamination of the water only arises if anaerobic conditions develop in the slurry deposits, giving rise to bacterial reduction of sulfate. If this is the case, HjS can be detected by smell in amounts which cannot be detected analytically or by taste. Remedial measures are dealt with in Section 20.4.2. 

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. 

Salt accumulations and other deposits on the firetube can sometimes be detected by smelling the vapors from the still vent. A burned" odor emitted from these vapors usually indicates this type of thermal degradation. Another detection method is to observe the glycol color. It will darken quickly if the glycol degrades. These detection methods may prevent a firetube failure. 

LPG is considered to be non-toxic witli no chronic effects, but the vapour is slightly anaesthetic. In sufficiently high concentrations, resulting in oxygen deficiency, it will result in physical asphyxiation. The gases are colourless and odourless but an odorant or stenching agent (e.g. methyl mercaptan or dimethyl sulphide) is normally added to facilitate detection by smell down to approximately 0.4% by volume in air, i.e. one-fifth of the lower flammable limit. The odorant is not added for specific applications, e.g. cosmetic aerosol propellant. 

Sulfur oxides (SO,) are compounds of sulfur and oxygen molecules. Sulfur dioxide (SO2) is the predominant form found in the lower atmosphere. It is a colorless gas that can be detected by taste and smell in the range of 1, (X)0 to 3,000 uglm. At concentrations of 10,000 uglm , it has a pungent, unpleasant odor. Sulfur dioxide dissolves readily in water present in the atmosphere to form sulfurous acid (H SOj). About 30% of the sulfur dioxide in the atmosphere is converted to sulfate aerosol (acid aerosol), which is removed through wet or dry deposition processes. Sulfur trioxide (SO3), another oxide of sulfur, is either emitted directly into the atmosphere or produced from sulfur dioxide and is readily converted to sulfuric acid (H2SO4). 

Intentional use of those senses that require contact with a material is NOT recommended for detection. Example smell, taste, feel. 

Many of the senses clues mentioned should be detected mechanically or chemically. In many cases, if you do personally smell something, it may be too late. However, if a product does have a distinctive odor or other characteristic, and you inadvertently encounter it (even though it is NOT recommended) then it is important that you recognize that the odor is a signal that you are being exposed to the material and that you should go to an uncontaminated area. 

Odor Relating to the sense of smell, a substance that stimulates the olfactory organ, allowing us to detect if a smell is pleasant or unpleasant. 

At 0.13 ppm by volume, H2S can be sensed by smell. At 4.6 ppm the smell is quite noticeable. As the concentration increases beyond 200 ppm, the sense of smell fatigues, and the gas can no longer be detected by odor. Thus, H2S cannot always be detected by smell. Even if H2S cannot be smelled, it is possible that there is sufficient H2S present to be life threat-... 

Can be detected by taste and smell 3 Easily noticeable odor... 

C. F. Schonbein detected and named ozone from its smell (see 1857). 

Ozone, O3, is the triatomic allotrope of oxygen. It is an unstable, blue diamagnetic gas with a characteristic pungent odour indeed, it was first detected by means of its smell, as reflected by its name (Greek o eiv, ozein, to smell) coined by C. F. Schonbein in 1840. Ozone can be detected by its smell in concentrations as low as 0.01 ppm the maximum permissible concentration for continuous exposure is 0.1 ppm but levels as high as 1 ppm are considered non-toxic if breathed for less than 10 min. 

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