Sulfur isotope pattern

The relevance of oxygen and sulfur isotopic patterns is nicely demonstrated by the cluster ion series in fast atom bombardment (FAB) spectra of concentrated sulfuric acid, where the comparatively large number of sulfur and oxygen atoms gives rise to distinct isotopic patterns in the mass spectrum (Chap. 9). 

The Hanna Basin coals from Wyoming had higher 63ife values than coals from the Powder River Basin. The pattern of sulfur isotopic composition found in coals from the Hanna Basin revealed that coals near the top of the coal seam contained more of the heavy sulfur isotope than coals stratigraphically lower in the coal seam. The sulfur isotope pattern observed in the Hanna Basin coals suggests that sulfur was introduced in sulfate-rich water from the top of the coal seam. 

Utilizing the presently available isotopic evidence (see Figure 32, and corresponding explanation below) for pinning down the emergence of this process, it would appear that a bacteriogenic sulfur isotopic pattern in sedimentary sulfides arose about 2.8 billion years ago. 

A pair on display in the American Museum of Natural History in New York has been split apart to show the structure inside, so that they look like a pair of lungs. Very old stromatohtes have been found with sulfur isotope patterns caught in the layers that suggest that they lived off sulfur cycles like the lowest layers in a Winogradsky column. These stone lungs breathed sulfur. 

Very old stromatolites have been found with sulfur isotope patterns. .. T. R. Bontognali et al. Sulfur isotopes of organic matter preserved in 3.45-billion-year-old stromatolites reveal microbial metabolism. 2012. Proc Natl Acad Sci. 109(38), p. 15146. DOl 10.1073/ pnas.1207491109. 

The mass spectrum of the unknown compound showed a molecular ion at m/z 246 with an isotope pattern indicating that one chlorine atom and possibly a sulfur atom are present. The fragment ion at m/z 218 also showed the presence of chlorine and sulfur. The accurate mass measurement showed the molecular formula to be C]3FI7OSCl R + DB = 10. 

The isotopic patterns of sulfur and silicon are by far not as prominent as those of chlorine and bromine, but as pointed out, their contributions are sufficiently important (Fig. 3.5). 

Fig. 3.5. Calculated isotopic patterns for combinations of elemental silicon and sulfur. The peak shown at zero position corresponds to the monoisotopic ion at m/z X. The isotopic peaks are then located at m/z = X+1, 2, 3,...

The El mass spectra of thiols and thioethers also show a series of onium ions generated by a-cleavage of the molecular ion (Table 6.9). Sulfonium ions can easily be recognized from the isotopic pattern of sulfur (Fig. 6.9). The fragmentation patterns of thioethers will be discussed in greater detail later (Chap. 6.5.2 and 6.12.4). 

Fig. 6.57. El mass spectmm of thiophene. The isotopic pattern of sulfur directly reveals its presence in the ions detected at m/z 45, 58, (69), and 84. Spectrum used by permission of NIST. NIST 2002.

The relatively intense isotope peaks separated by 2 mass units for Cl or Br provide a rapid indication of the presence of these elements in an analyte. Dichloro and dibromo compounds give similarly distinctive patterns, as shown in Figures 5.20 and 5.21. Other elements have similarly recognizable isotopic patterns, e.g. sulfur, although none is as distinctive as those for Cl and Br. 

Winner, W.E., Smith, C.L., Koch, G.W., Mooney, H.A., Bewley, J.D., and Krouse, H.R. (1981) Rates of emission of H2S from plants and patterns of stable sulfur isotope fractionation. Nature 289, 672-673. 

The isotopic pattern may complicate the molecular weight assignment on the other hand, it will also provide valuable reference for recognizing the type and number of element in a molecule. The characteristic patterns resulting from multiple isotopic contributions of the chlorine, bromine, and sulfur isotopes are shown in Table 7-5. One example is illustrated in the CI-MS spectrum of mometasone furoate (Figure 7-2), displaying prominent... 

The earliest isotopic record of sedimentary pyrite in the Archean lacks the large spread between coeval sulfate and sulfide sulfur that characterizes the Phanerozoic data. Sedimentary sulfides formed between 3.4 Ga and 2.7 Ga have isotopic compositions within 5%c of contemporaneous seawater SO . This change in isotopic pattern compared to Phanerozoic data is to be expected if atmospheric O2 was low, and consequently no widespread mechanism existed for oxidizing reduced sulfur to form 804 in seawater. Sulfate concentrations <200 p,M are required to suppress isotope fractionation by SRB (Habicht et al., 2002). Most researchers hold to a scenario that photosynthetic production of O2 began by 2.7 Ga, but that there was a lag of several hundred million years before atmospheric O2... 

Schwarcz and Bumie (1973) reviewed sulfur isotope abundances in strata-bound sulfide deposits in clastic sediments not associated with volcanic rocks and concluded that two patterns were evident. One was a broad distribution ranging from arotmd the 5 S of sea water to values 25%o lower while the other was a narrow distribution around a 5 8 of —50%o with respect to oceanic sulfate. The former pattern was identified with shallow marine or brackish-water environments while the latter occurred in deep, euxinic basins. They explained the first distribution on the basis of Fig. 6.2.4a and assumed a closed system with an average 32/ 34 ratio of about 1.025. The second distribution pattern applied to deep basins and Schwarcz and Bumie (1973) concluded that the systems were fully open, in which case the isotopic selectivity was much larger as is the case in a number pf modem euxinic basins (e.g. Black Sea see pp. 338, 412). 

Compounds containing elements other than chlorine such as bromine or sulfur which compromise the isotope pattern ... 

Dichloromethane extracts and thermal desorption The chromatograms of the samples (Fig. 12) showed main peaks at 9.04, 11.61, 13.85, 17.45 and 17.87 min. Chlorodiphenylarsine (Clark I, 9.04 min), Triphenylarsine (11.61 min) and Bis(diphe-nylarsine)oxide (17.45 min, main degradation product of Clark I) could be identified using library searches. Bis(diphenylarsine) (17.87 min) has been identified by means of its mass spectra according to Schoene et al. (1995). Isotopic pattern calculation indicated the peak at retention times 13.85 min to contain sulfur. By comparison of the mass spectrum the substance could be identified as Diphenylthiophenylarsine as proposed by Schoene et al. (1995). 

Austin S. R. Some patterns of sulfur isotope distribution in uranium deposits. Earth Sci. Bull., 3, no. 2 1970, 5—22. 

An interesting feature in order to generate molecular formulas and to facihtate an extra confident identification is the use of different isotopic filters. These filters work based on the isotopic pattern deviation between the empirically measured and the theoretical spectrum. The presence of an abundant isotopic pattern in the analyte molecule helps to confirm the presence of that compound in the sample. Thus, the presence of atoms such as carbon, chlorine, bromine, or sulfur in the molecule gives a characteristic isotopic pattern that allows reducing the number of possible elemental compositions fora certain mass-accuracy window. The match between empirical and theoretical data is given by the isotope fit (i-FTT) or sigmaFlT values. These values are calculated, taking into account not only the isotopic distribution but also the accurate masses. The lower the value, the more plausible the elemental composition (Ojanpera et al., 2006 Ibanez et al., 2008). 

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