Sulfur-containing compounds, detection

Figure 5. Effect of purge temperature on the analysis of beef sulfur-containing compounds. Detection of the sulfur-containing volatiles was by flame photometric detection. Samples were analyzed using the external closed inlet device (ECID) described previously (i). Rates of change in compond composition during storage over a 4 day period was determined from the data in ref. 14.

Amperometric detection utilizes a current to initiate a chemical conversion of electroactive analytes. Different factors such as temperature, pH, and mass transfer are to be considered and controlled in order to obtain stable and reproducible results. Examples of sulfur-containing compounds detectable by amperometric detection are sulfite and thiocyanate [3]. 

Phosphorous- and sulfur-containing compounds separated by GC have been determined with both He and N2 MIP-MS systems with low ng to pg detection limits [335], Halogenated compounds and organotins can be determined by GC-MIP-MS, at low to sub-pg detection limits. 

Walash et al. [14] described a kinetic spectrophotometric method for determination of several sulfur containing compounds including penicillamine. The method is based on the catalytic effect on the reaction between sodium azide and iodine in aqueous solution, and entails measuring the decrease in the absorbance of iodine at 348 nm by a fixed time method. Regression analysis of the Beer s law plot showed a linear graph over the range of 0.01 0.1 pg/mL for penicillamine with a detection limit of 0.0094 pg/mL. 

Element-specific detection combined with capillary GC has become a key technique in the chemical communication studies of our laboratory. An effective detector of this type is based on the microwave plasma emission (Wylie and Quimby 1989), with a tunable selectivity for several elements and a prominent sensitivity for sulfur-containing compounds, which is significantly greater than... 

Sulfur dioxide is a colorless gas with a sharp, pungent odor, like that of a burning match. Most people are able to detect this highly characteristic odor at concentrations of about 0.5 ppm or greater. Its chemical formula is SO2. Sulfur dioxide is readily soluble in water, forming the weak acid sulfurous acid (H2SO3). Sulfur dioxide is formed when sulfur or a sulfur-containing compound is burned ... 

Fig. 2. Separation and analysis of polyaromatic sulfur-containing compounds (PASC). Oils 3-1, 3-2, and 3-3 were analyzed by gas chromatography-mass spectroscopy (GC-MS) and gas chromatography-atomic emission detection (GC-AED). Reproduced from Ref. 12, with permission.

Wool, which is used as indoor floor covers, clothing and in many other consumer products, can emit a wide variety ofVOCs, many of which have strong odor. Lisovac and Shooter (2003) have shown that several VOCs can be detected in headspace sampling of wool and wool waxes. A number of these are odorous sulfur-containing compounds while the non-sulfur containing components include hydrocarbons, alcohols, aldehydes and ketones, the most prominent of which are 3-methylpen-tane, hexane, methylcylopentane, toluene, 2-methylpentane, ethanol, 1-butanol, pentanal, hexanal acetone, and 2-butanone. 

A heterocyclic sulfur-containing compound, 2-methyl-thiophene, was identified in boiled crayfish tail meat and pasteurized crabmeat. Thiazole and 3-methylthiopropanal were identified in the crayfish hepatopancreas. Heterocyclic sulfur-containing compounds play important roles in generating meaty aromas in a variety of meat products and are considered important volatile aroma components of marine crustaceans (12— 14). The 2-methylthiophene could be an important flavor cemponent in boiled crayfish tail meat. Both thiazole find 3-methylthiopropanal were important contributors to the desirable meaty aroma associated with crayfish hepatopancreas. The 3-methyl-thiopropanal, identified in boiled crayfish hepatopancreas, is derived from Strecker degradation of methionine (15), and has been considered to be an important cemponent in basic meat flavor (16). Pyridine was detected in the headspace of the hepatopancreas from freshly boiled crayfish. Pyridine and 2-ethylpyridine have been previously reported as components in the atmospheric distillate from a sample of crayfish hepatopancreas frozen for three months (2). 

The non-polar chlorinated hydrocarbon pesticides are routinely quantified using gas chromatography (GC) and electron capture(EC) detection. Alternate detectors include electrolytic conductivity and microcoulometric systems. Organophosphate pesticides which are amenable to GC are responsive to either the flame photometric detector (FPD) or the alkali flame detector (AFD). Sulfur containing compounds respond in the electrolytic conductivity or flame photometric detectors. Nitrogen containing pesticides or metabolites are generally detected with alkali flame or electrolytic conductivity detectors. 

Figure 5. MEKC electropherogram of six sulfur-containing compounds related to the degradation of mustard and 0-alkyl alkylphosphonothiloates (solute concentration 50mgL ) TDGO (1), TDG (2), Thioxane (3), IBMPSA (4), Dithiane (5), and EMPSA (6). MEKC conditions 57cmLt (50cmLj) x 75 rm ID V = 25kV Buffer lOmM borate, 100 mM SDS, pH 9 direct UV detection at 200 nm. (Reprinted from R.L. Cheicante, J.R. Stuff, and H.D. Durst, J. Chromatogr., A, 711, 347-352 (1995), reproduced with permission from Elsevier Science)...

Casella, I. G., Contursi, M. and Desimoni, E. (2002), Amperometric detection of sulfur-containing compounds in alkaline media. Analyst, 127(5) 647-652. 

In trace analysis of contaminant substances, one can use specific detectors for certain compounds, such as a nitrogen-phosphorus detector (NPD), thus gaining detection ability for nitrogenated and phosphorylated compounds the electron-capture detector (ECD) shows excellent performance for chlorinated substances and the flame photometric detector (FPD) is the most widely used for sulfur-containing compounds. 

Pyrolysis products of chlorinated polyethylene contain molecules similar to those found in polyethylene pyrolysates and, in addition, compounds similar to that obtained from vinyl chloride (significant amount of HCI). Chlorosulfonated polyethylene typically contains only about 1.5% sulfur, but sulfur-containing compounds such as SO2 can be detected among its pyrolysis products. The distribution of chlorine atoms in chlorinated polyethylene has been investigated using Py-GC [55, 56]. The polymer was considered equivalent with a terpoiymer poly[ethylene-co-(vinyl chloride)-co-(1,2-dichloroethylene)]. The level of specific degradation products such as aromatic molecules (benzene + toluene + styrene + naphthalene), chlorobenzene, and dichlorobenzenes correlates well with the carbon/chlorine ratio in the polymer. 

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 ... 

Similarly to the case of PES, pyrolysis of bisphenol A polyethersulfone (PES) is very likely radicalic, and the compounds generate by the termination reaction with reaction of two free radicals include dibenzofuran, 4-methyl-dibenzofuran, etc. Also during pyrolysis of PSF it is possible that diphenylsulfone and other sulfur-containing compounds are formed but are not detected in the analysis step. The SO2 group represents 14.48% of the weight of PSF, and only 8.37% molecular SO2 is detected in the pyrogram shown in Figure 12.2.3. 

Spot Mercaptans and thioketones markedly catalyze the reaction of sodium azide with iodine with liberation of nitrogen, and this catalyst is used for detection of the sulfur containing compounds. 

Hydrogen sulfide is a colorless, flammable gas with important chemical and toxicological properties. It is the product of a number of natural processes, including the decay of sulfur-containing material. Its noxious odor of rotten eggs permits its detection at extremely low concentration (0.02 ppm). Because the olfactory sense is dulled by its action, however, higher concentrations may be tolerated, and the lethal concentration of 100 ppm may be exceeded. Aqueous solutions of the gas were used traditionally as a source of sulfide for the precipitation of metals, but because of the toxicity of H2S, this role has been taken over by other sulfur-containing compounds such as thioacetamide. 

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