Volatile compounds quantity

The parent methylenecyclopropane (MCP) (1) [1 ] is a highly volatile compound (bp 11 °C) which can be prepared in multigram quantities and is commercially available. Numerous efficient and straightforward syntheses of the different types of methylene- and alkylidenecyclopropanes have appeared in the literature and the matter has been reviewed by Binger and Buch [2]. In the last decade other selective syntheses have been developed which gave easy access to compounds containing specific substitution patterns [3], to optically active derivatives [4], or more sophisticated derivatives like dicyclopropylideneethane (2) [5], bicyclopropylidene (BCP) (3) [6] and chloromethoxy carbonyl-methylenecyclopropane (4) [7],... 

Based on the quantitative determination of pentadecane it was calculated that—with a sample load of about 200pg—alkanes are detected by this screening method if their concentration is 5ppm or more. It is obvious that highly volatile compounds when present as such (e.g. dioxane) cannot be measured quantitatively because considerable losses of such components occur during the evaporation of the suspension liquid from the pyrolysis wire when it is prepared. Quantities measured for such compounds must therefore be considered as minimum values. 

Several sampling procedures are applicable to volatile compounds but method application often depends on the compound(s) to be sampled (Dean, 2003). Part of the issue of sampling volatile compounds arises because some volatile substances sublime rather than boil, whereas other volatile substances emit significant quantities of vapor well below their boiling point. For sampling volatile hydrocarbons in the field, two procedures are generally recommended zero headspace and solvent extraction. However, these two procedures do not necessarily give equivalent results. 

The effect of temperature on the solubility of 5b was investigated in a series of experiments at the same CO2 density (p = 0.75 gcm ). The temperature that generally may affect the solubility of volatile compounds in compressed fluids has only a minor impact on the solubility of the relatively low volatile complex 5b in the investigated range (Fig. 12). At temperatures between 313 and 333 K, approximately the same quantities of 5b are extracted. 

The most difficult problem in flavour research is to interpret the results of the volatile analysis, which gives information on the identity and the quantity of the volatile compounds collected from a given product. Many volatile compounds are not flavour-active, i.e. they cannot be detected in the olfactory system, while others may even in trace amounts have significant effects on flavour owing to their low odour-threshold values that is defined as the minimum concentration needed to produce an olfactory response. Consequently, the most abundant volatiles are not necessarily the most important contributors to flavour. Much... 

Sugars, acids and aroma compounds contribute to the characteristic strawberry flavour [85]. Over 360 different volatile compounds have been identified in strawberry fruit [35]. Strawberry aroma is composed predominately of esters (25-90% of the total volatile mass in ripe strawberry fruit) with alcohols, ketones, lactones and aldehydes being present in smaller quantities [85]. Esters provide a fruity and floral characteristic to the aroma [35,86], but aldehydes and furanones also contribute to the strawberry aroma [85, 87]. Terpenoids and sulfur compounds may also have a significant impact on the characteristic strawberry fruit aroma although they normally only make up a small portion of the strawberry volatile compounds [88, 89]. Sulfur compounds, e.g. methanethiol. 

There have been many reports of the wandering of polonium from open sources, behavior at one time attributed to an aggregate recoil mechanism (84), but more recent observations with curie quantities indicate that contamination only spreads when volatile compounds, for instance polonium tetrachloride, are involved. 

Static mode the sample (liquid or solid matrix) is placed in a glass phial capped with a septum such that the sample occupies only part of the phial s volume. After thermodynamic equilibrium between the phases has been reached (1/2 to 1 h), a sample of the vapour at equilibrium is taken (Fig. 20.4). Under these conditions, the quantity of each volatile compound present in the headspace above the sample is proportional to its concentration in the matrix. The relationship between the amount of sample injected into the gas chromatograph and its concentration in the matrix can be obtained by calibration (using internal or external standards). 

Adsorbent traps can be used to concentrate volatile compounds without solvents so that the minute quantities present in a product (often ppb levels for odor-impact compounds) can be detected. Three steps are involved (1) concentration of headspace gas on a trap,... 

Use of GLC to determine qualitative and quantitative composition of volatile compounds in citrus oils has become common. However, there are many discrepancies in the literature concerning the quantitative composition of citrus oils. Analyses of volatile aldehydes are of major importance, because composition and quantity of these compounds influence the quality and value of citrus oils. Compositional differences between... 

Occupational settings provide the greatest potential for high exposures to chlorobenzene. Since chlorobenzene is a volatile compound and is used extensively as a solvent, large quantities may be released to the workplace air. Other populations who might be exposed include persons living near industrial facilities where chlorobenzene emissions are not properly controlled. 

Method whereby volatile compounds are separated by injecting them into a stream of inert gas which percolates over a solid or liquid stationary phase. The separated compounds are then detected and quantified by means of an electrochemical or fluorescent probe. GC-MS is a method whereby the gas chromatograph is linked to a mass spectrograph, thereby allowing very small quantities of the compound to be quantified. 

Ruminant animals produce dimethylsulfide, a fraction of which is exhaled.4 Therefore, cows breath is a source of this compound in terrestrial atmospheres. Dimethylsulfide is produced in enormous quantities by marine organisms. This volatile compound is the largest source of biogenic sulfur in the atmosphere and is responsible for some of the odor emanating from coastal mud flats. 

Table II. Quantity of Some Major Volatile Compounds Formed in the Interaction of 2,4-Decadienal with Cysteine or Glutathione...

Analysis by GC-MS. The four GC patterns obtained were each unique in the number of separated peaks as well as their quantity. Crude oat oils (COUM, COUC) differed from similar heated oils (CORM, CORC). For explanation of the abbreviations used, see Legend of Symbols. Oat samples milled after roasting (MARM, MARC) contained more volatile compounds, both with regard to number and quantity, compared with identical samples milled before roasting (MBRM, MBRC). In addition, volatile constituents from the Chihuauhua variety (MARC, MBRC) were present in lower concentrations than the Magne variety (MARM, MBRM). 

Ten volatile compounds were produced from the pyrolysis of 6-carotene. Among them, toluene, xylene, IJ-cyclocitral, ionene, B-ionone, 5,6-epoxy-B-ionone and dihydroactinidiolide were identified. The addition of catechin gallates reduced the quantity of the ten... 

Volatile compounds generated by model systems of zeln, corn amylopectin and corn oil extruded at barrel temepratures of 120°C and 165°C were analyzed by GC and GC/MS. The largest quantities of lipid oxidation products were detected in systems containing all three components. In each system, the quantity of 2,4-deca-dienal was low relative to the quantities of hexanal, heptanal and benzaldehyde. Identification of the Maillard reaction products, 2-methyl-3(or 6)-pentyl-pyrazine, 2-methyl-3(or 6)-hexylpyrazine and 2,5-di-methyl-3-pentylpyrazine, suggested that lipid-derived aldehydes might be involved in the formation of substituted pyrazines. 4-Methylthiazole was identified as a major decomposition product of thiamin when corn meal containing 0.5% thiamin was extruded at a final temperature of 180°C. 

The aroma of mangosteen is contributed by 52 volatile compounds, 28 of which have been identified. In terms of quantity, the major compounds are (Z)-hex-3-en-l-ol (27%), octane (15%), hexyl acetate (8%) and a-copaene (7%). The main contributors to the mangosteen flavour are hexyl acetate, (Z)-hex-3-enyl-acetate (cis-hex-3-enyl-acetate) and (Z)-hex-3-en-l-ol (MacLeod and Pieris, 1982). The major groups of compounds found in mangosteen aril are alcohols, aldehydes and ketones, esters, hydrocarbons, terpenes, etc. The compounds present are given in Table 19.3. 

For the more volatile compounds such as HCB and the HCHs, evaporation will be the major loss mechanism over a relatively short period of time. For compounds with higher adsorption, such as DDT, residual quantities may... 

Contrary to some reports,1 3 ditechnetium heptaoxide is not the only product formed when technetium metal is burned in an excess of oxygen—nor can it be purified by simple resublimation. The formation of small quantities of a second volatile compound (possibly Tc03 or HTc04) has been observed by some investigators.4 6... 

When a volatile compound is introduced into the carrier gas and carried into the column, it is partitioned between the gas and stationary phases by a dynamic countercurrent distribution process. The compound is carried down the column by the carrier gas, retarded to a greater or lesser extent by sorption and desorption in the stationary phase. The elution of the compound is characterized by the partition ratio, k, a dimensionless quantity also called the capacity factor. It is equivalent to the ratio of the time required for the compound to flow through the column (the retention time) to the retention time of a nonretarded compound. The value of the capacity factor depends on the chemical nature of the compound the nature, amount, and surface area of the liquid phase and the column temperature. Under a specified set of experimental conditions, a characteristic capacity factor exists for every compound. Separation by gas chromatography occurs only if the compounds concerned have different capacity factors. 

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