Sulfur compounds sample preparation

Acetaldehyde [75-07-0] (ethanal), CH CHO, was first prepared by Scheele ia 1774, by the action of manganese dioxide [1313-13-9] and sulfuric acid [7664-93-9] on ethanol [64-17-5]. The stmcture of acetaldehyde was estabhshed in 1835 by Liebig from a pure sample prepared by oxidising ethyl alcohol with chromic acid. Liebig named the compound "aldehyde" from the Latin words translated as al(cohol) dehyd(rogenated). The formation of acetaldehyde by the addition of water [7732-18-5] to acetylene [74-86-2] was observed by Kutscherow] in 1881. 

Sulfur-containing samples show colored spots when sprayed with 2,6-dibromo-quinone-4-chlorimide Gibbs reagent). For preparation, 2 g of this compound is dissolved in 100 ml of acetic acid or ethanol. Heating to 110°C is necessary to give a reaction. This reagent also creates colored zones when samples contain phenols. For reactions with phenols, only the less-reactive 2,6-dichloroquinone-4-chlorimide can be used under the same conditions. 

DL-Dihydrostreptose and its ribo isomer were similarly obtained. Birch reduction of 2-methyl-3-furoic acid, followed by addition of methanol, bromination, and dehydrobromination, gave 402 as a mixture of the isomers. Hydroxylation of 402 with osmium tetraoxide-so-dium chlorate, and subsequent treatment with acetone-sulfuric acid afforded three isomeric acetals (403-405). The structures of these compounds were assigned on the basis of their H-n.m.r. spectra. In addition, the relationship between 403 and 404 was established by hydrolysis and reglycosidation. The methyl esters 403-405 were quantitatively reduced to the corresponding alcohols. The mixture of alcohols obtained from 403 and 404 was converted into crystalline 5-deoxy-3-C-(hydroxymethyl)-l,2-0-isopropylidene-a-DL-ribofuran-ose (406), which was compared directly with a sample prepared from D-xylose. Methyl 5-deox y-3-C-(hydroxy methyl)-2,3-O-isopropy lidene-/3-DL-lyxofuranoside (407), obtained by reduction of 405 with lithium aluminum hydride, was hydrolyzed with dilute hydrochloric acid, to give a,/3-DL-dihydrostreptose.2,ifi... 

The polarographic and potentiometric methods are not HPLC-run. The polarographic method relies upon the measurement of half-wave potentials of various sulfur compounds reacting with a mercury electrode. It is sensitive to submicromolar concentrations (Luther, pers. com.). While sulfide, thiosulfate, polysulfide and polythionates can be measured, the initial sample must be subdivided and pretreated in different ways. The disadvantages are that sample preparation ana analysis are time-consuming and there is no way to preserve samples for later analysis nor to study organic thiols with precision., ... 

Volatile profiles of raw and cooked-beef flavor samples, prepared by the procedures of Figure 1, were obtained after capillary GC and FPD. Although the identification of these sulfur containing compounds is as yet incomplete, the chromatograms demonstrated that there were a number of new sulfur compounds produced on cooking that were not present in the raw beef. Three prominent sulfur compounds were identified as markers in subsequent meat flavor deterioration experiments, namely, methional (13.2 min), methyl sulfone (13.8 min), and benzothiazole (25.3 min). Each compound produced an adequate mass spectrum for spectral library search and positive identification. 

Modem GCMS analysis and sample preparation techniques have overcome many the analytical problems associated with the investigation of organic sulfur compounds associated with potential reactions between elemental sulfur and organic matter during analysis (Hayes, 1967). Shimoyama and Katsumata (2001) examined the distribution of aromatic thiophenes in Murchison detecting benzothiophene, dibenzothiophene, alky-substituted dibenzothiophenes, and benzo-naphthothiophenes at concentrations levels of 0.3 ppm (Table 1) confirming earlier studies (Basile et al., 1984). 

In the current study, special attention was given to confirming the presence of carbon disulfide in the headspace of Cheddar cheese, and conclusive mass spectral evidence was developed for this compound. The concentration of carbon disulfide varied widely in the samples analyzed for the methanethiol studies, and became quite abundant in the most-aged sample of cheese that contained the encapsulated methioninase system (Figure 6). This sample also contained a lower molecular weight sulfur compound which remains unidentified, but it was observed only in the cheese prepared with encapsulated methioninase. 

Naphthalene, obtained from a petroleum reformate, was chromato-graphically pure after recrystallization. The two monomethylnaph-thalenes were obtained by distillation from the same reformate. The 1-methylnaphthalene was a heart cut of 99-f% purity from a precise fractional distillation. 2-Methylnaphthalene from the same distillation was recrystallized to high purity. 1,3-Dimethylnaphthalene, 1,7-dimethylnaphthalene, and 1,8-dimethylnaphthalene were synthetic samples that were kindly donated by Dr. G. D. Johnson of Kansas State University and Dr. L. Friedman of Case Institute. The remaining isomers were obtained from commercial sources. They were treated with Raney nickel in methanol under reflux to destroy catalyst poisons such as sulfur compounds. The liquid isomers were further purified by preparative-scale gas chromatography. Octalins were prepared by reducing pure naphthalene with lithium in ethylamine (29). 

Selective detectors are especially useful for the analysis of various contaminants in increasingly complex matrices because they largely avoid interference. They can shorten the analysis time by eliminating laborious, time-consuming sample preparation procedures that can also often cause the contamination or loss of analytes. For these reasons selective detectors have been extensively used in the determination of environmental sulfur compounds. 

It has been found that when the mixture is heated at such a high temperature, a considerable amount of sulfur trioxide is expelled from the melt, while phosphorus pentoxide is not expelled. Chemical analyses of the reaction products revealed that 63.5 and 80.8% of the total sulfur was expelled as sulfur trioxide when prepared at 1300 or 1400°C., respectively. If one assumes that no compounds with S-O-P linkages are produced in the sample, the reaction can be represented by ... 

There are those happy users who dissolve their sample in the mobile phase and inject right away. If you are one of these and you also have isocratic conditions with acetonitrile/water, you can forget about sample preparation for now. There are however those users who need to quantify minor unknown impurities of a metabolized metabolite from bile fluid and others who hunt after heterocyclic sulfur-containing compounds in crude oil residue from Iran and compare it with Iraqi oil. They all have my sympathy. In the following table, a few typical errors occurring in a normal sample preparation are listed. 

A simple method was employed to prepare a base wine for constructing a calibration curve for the quantification of the reductive sulfur compounds. Deodourisation of the base wine was carried out in order to remove the volatile sulfur compounds as much as possible, along with other volatile compwimds, while retaining further components of the wine to obtain a matrix effect similar to that of a wine sample. 

Table 3. Selected sample preparation conditions for HS-SPME extraction of the reductive sulfur compounds...

With this in view, automatic isotcpe analytical processes have been developed. Of these methods, the sample preparation techniques used for simultaneous determination of carbon-14/ tritium and carbon-14/sulfur-35 in dual labelled organic compounds and biological materials hy liquid scintillation counting are presented. For the determinaticai of carbon-14/sulfur-35 an iirproved versicai of a previously published method (Gacs et al., 1978a) is described. The principles of the procedures are shewn in Fig.l and Fig.2. 

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