Sulfur-containing volatiles, molecular

At 75 C all six major sulfur-containing volatiles are observed. These include hydrogen sulfide, carbonyl sulfide, and methane thiol as low molecular weight components and dimethyl sulfide, dimethyl disulfide, and dimethyltrisulfide as the higher molecular mass sulfur-containing compounds. During refrigerated... 

They fractionated the melanoidins by gel filtration to determine which molecular weight melanoidins were responsible for this loss. They found that aU of the fractions reacted with the sulfur-containing volatiles. Attanpts to free the melanoidin-bound volatiles through the addition of other free thiols were unsuccessful, suggesting that the sulfur compounds were not simply involved in disnlfide interchange as observed for proteins. Further work strongly supports the hypothesis that the thiols are covalently bound to pyrazinium ions which are oxidation products of l,4,-bis-(5-amino-5-carboxy-l-pentyl) pyrazinium radical ions. 

Other anal sac constituents which are commonly encountered products of microbial activity include trimethylamine, noted in the anal sac secretions of the red fox (42), coyote and domestic dog [36), and the aromatic acids phenylacetic acid and 3-phenyl-propionic acid (and related phenolic acids), together with the diamines putrescine and cadaverine as well as ammonia in the anal sac secretions of the red fox and the lion (25,29,35). Indole has also been noted. The lower molecular weight lipids of lion anal sac secretion include many substances expected as hydrolysis products of sebaceous lipids (2. Red fox anal sac secretion also exhibits an anomalous free amino-acid composition with 5-aminovaleric acid predominating ( ). The possibility that the sulfur-containing volatiles present in mustelid anal sac secretions are of microbial origin is at present under investigation in our laboratories. 

Diphenylsulfone was not detected in the pyrolysate, either because it is not formed at detectable levels, or because it may not elute from the Carbowax column used for the separation of the pyrolysate. However, this compound and other sulfur-containing compounds may be formed during pyrolysis and not detected in the analysis step. The SO2 group represents 27.58% of the weight of the polymer, and only 19.94% molecular SO2 is detected in the pyrogram (assuming equal detector response for all analytes). The other sulfur-containing compounds except for diphenylsulfide (0.33%) and dibenzothiophene (0.72%) are at a trace levels. The thermal decomposition of PES takes place, very likely, by a radicalic mechanism, and the free radicals can interact and form other stable molecules such as biphenyl ( 4 % of volatile pyrolysate), 4-hydroxybiphenyl ( 2% of volatile pyrolysate) and dibenzofuran ( 12% of volatile pyrolysate) which are shown below ... 

The flavor of fish and seafoods is composed of taste-active low molecular-weight extractives and aroma-active compounds. The taste-active compoimds are more abundant in the tissues of mollusks and crustaceans than fish. The most important non-volatile taste components are fi-ee amino acids, nucleotides, inorganic salts and quaternary ammonia bases. Alcohols, aldehydes, ketones, furans, nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, esters and phenols are the most important volatiles is shellfish. Alkyl pyrazines and sulfur-containing compounds are important contributors to the cooked aroma of crustaceans. Furans pyrazines, and Lactones have been found in heat-treated seafoods. Dimethyl disulfide, dimethyl trisulfide, heterocyclic sulfiir-containing compounds (alkylthiophenes) have been found in most thermally treated crustaceans like prawn, crab, oyster, crayfish and shrimp (52). 

Thallium is one of the most difficult elements for GF AAS, at least when it has to be determined in complex matrices, as will be shown in more detail in Sections 8.2.6 and 8.2.7. Thallium forms a chloride that is volatile at temperatures above 400 °C and easily lost without being atomized, as the gaseous molecule HCl is thermally very stable. Palladium, the most frequently used modifier to avoid such losses, has an absorption line close to the T1 line, causing a spectral interference. Iron, a frequent concomitant in many samples, also has an absorption line close to the T1 line. Finally, sulfur-containing samples produce a molecular absorption spectram with a pronounced rotational fine stfucture, which is another source of spectral interferences [141]. 

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. 

When coals are pyrolyzed, this process is continued by the near complete elimination of hydrogen and oxygen. The carbon residue that remains, however, still contains small quantities of nitrogen and sulfur. Typical values for carbon, hydrogen, volatile matter (i.e., low-molecular-weight products of the pyrolysis), and residual (fixed, nonvolatile) carbon of the various classes of coal (Table 6.1) provide the basis of a system for describing coal rank (Chapters 2 and 8). 

Several gas-solid adsorption capillary columns are available. They are commonly called porous-layer open tubular or PLOT columns. These columns contain a layer of adsorbent particles coated on the irmer wall of the fused silica tubing. Phases of aluminum oxide (alumina), molecular sieves, and porous polymers (Poraplot-like) are commercially available. Gas-solid adsorption rather than a gas-liquid partition is the separation mechanism involved. PLOT columns are well suited for the analysis of light hydrocarbons, sulfur gases, permanent gases, or other very volatile solutes at or... 

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