Isotope selenium

Formation of a new compound PSeF3 has been claimed in the reaction of PF3 with elemental selenium, at 300-400°C, identified from a mass spectrum analysis, showing the fragments (PSeF2)+ with the expected selenium isotopes (34). However, since no further data have been obtained, it appears very likely that the compound actually was... 

SELENIUM ISOTOPE APPLICATIONS AND DATA FROM NATURAL MATERIALS... 

Hagiwara Y (2000) Selenium isotope ratios in marine sediments and algae. A reconnaissance study. M.S. 

Johnson TM (in press) A review of mass-dependent fractionation of selenium isotopes and implications for other heavy stable isotopes. Chem Geol... 

Johnson TM, Bullen TD (2003) Selenium isotope fractionation during reduction by Fe(ll)-Fe(lll) hydroxide-sulfate (green rust). Geochim Cosmochim Acta 67 413-419 Johnson TM, Bullen TD, Zawislanski PT (2000) Selenium stable isotope ratios as indicators of sources and cycling of selenium Results from the northern reach of San Francisco Bay. Environ Sci Tech 34 ... 

Rees CB, Thode HG (1966) Selenium isotope effects in file reduction of sodium selenite and of sodium selenate. Can J Chem 44 419-427... 

Webster CL (1972) Selenium isotope analysis and geochemical applications. Ph.D Dissertation, Colorado State University, Fort Collins, CO... 

Because selenium to some extent is chemically similar to sulfur, one might expect to find some analogous fractionations of selenium isotopes in nature. Six stable selenium isotopes are known with the following abundances (Coplen et al. 2002)... 

Hendy CH, Wilson AT (1968) Paleoclimatic data from speleothems. Nature 219 48-51 Heraty LJ, Fuller ME, Huang L, Abrajano T, Sturchio NC (1999) Isotopic fractionation of carbon and chlorine by microbial degradation of dichlormethane. Org Geochem 30 793-799 Herbel MJ, Johnson TM, Oremland RS, Bullen TD (2000) Fractionation of selenium isotopes during bacterial respiratory reduction of selenium oxyanions. Geochim Cosmochim Acta 64 3701-3710... 

Figure 16-17 Electron paramagnetic resonance spectrum of the Fe-S protein putidaredoxin in the natural form (32S) and with labile sulfur replaced by selenium isotopes. Well-developed shoulders are seen in the low-field end of the spectrum of the 77Se (spin = l/2)-containing protein. From Orme-Johnson et al.29S Courtesy of W. H. Orme-Johnson.

As in years past, the published thiophene literature dwarfs the selenophene and tellurophene literature. However, there was a significant increase in the number of interesting selenophene and tellurophene references last year. The preparation of T)5-selenophene complexes of chromium, magnesium, ruthenium and iridium were studied <950M332>. These studies took advantage of the NMR-active selenium isotope 77Se (7.58% natural abundance) as a tool to directly study binding of selenophene derivatives to a catalyst surface. 

The electron impact mass spectra of a series of selenazoles have been compared with those of their thiazole analogs. The results indicate that, in general, the mass spectrometric fragmentation patterns of the selenium heterocycles can be predicted by an examination of the corresponding sulfur analog. One of the characteristics of the mass spectra of selenium compounds is that they are rich in ions due to the presence of the six relatively abundant stable selenium isotopes (81JHC1335). 

J. J. Sloth, E. H. Larsen, The application of inductively coupled plasma dynamic reaction cell mass spectrometry for measurement of selenium isotopes, isotope ratios and chromatographic detection of selenoamino acids, J. Anal. Atom. Spectrom., 15 (2000), 669-672. 

In this method, samples are spiked with a known amount of an enriched isotope of selenium ( Se in this case) and wet digested to destroy the organic matter and render all of the selenium into the oxidation state. Next, the selenium is reacted with 4-nitro-o-phenylenediamine (NPD) to form the nitropiazselenol (Se-NPD) which is extracted into chloroform. Aliquots of the extract are then introduced into the mass spectrometer (MS) via a gas chromatograph (GC) and individual ions measured to determine isotope ratios of the various selenium isotopes. From the observed isotope ratios and the known amount of Se spike added, the amounts of enriched tracer (e.g.,... 

Modern thermal ionization mass spectrometry (TIMS) is now sufficiently sensitive and precise to measure individual selenium-isotope abundances (e.g., Se/ Se) in solid samples or residues so that it can be used to study environmental cycling/distri-butions (Johnson era/., 1999). Microbial reduction of selenate leads to isotopically lighter selenite, i.e., the reduction has a Se/ Se fractionation factor, , of about — 5.5%o (Johnson et al., 1999). INAA has been used to determine different selenium isotopes, especially Se in plant tracer studies. 

Selenium isotope ratios as indicators of selenium sources and oxyanion reduction. Geochim. Cosmochim. Acta 63, 2775-2783. 

Inductively coupled plasma mass spectrometry (ICP-MS), a relatively novel technique with high sensitivities for most elements, presents major attributes not available with other methods of isotopic analysis simple requirements for chemical processing, high sample throughput, acceptable level of measurement precision and bias, multi-element capability and reasonable accessibility and capital cost. The relatively low sensitivity for selenium, however, precludes the direct measurements in clinical matrices without analyte preconcentration (Hieftje and Vickers. 1989). The present state of development of ICP-MS for application to clinical matrices indicates that the technique can provide selenium isotope ratio measurements with the required accuracy and precision (Ting and Janghorbani, 1987 Ting et al., 1989). 

Reamer. D.C. and Veillon, C. (1983). A double isotope dilution method for using stable selenium isotopes in metaboloic trace studies anaiysis by gas chromatography/mass spectrometry (GC/MS). J. Nutr. 113, 786. 

The gaseous fission product releases were calculated for the two reference isotopes Kr-85m and Xe-138. Nominal values for the material properties were used in the calculation. The releases for other isotopes can be obtained by assuming that the release-rate-to-birth rate ratio (R/B) varies as the square root of Isotope half-life. Moreover, it is conservatively assumed that bromine and selenium isotopes have the same release characteristics as krypton, and that iodine and tellurivun isotopes have the same release characteristics as xenon. 

The thermally induced redistribution of the tellurium and selenium isotopes shown under certain conditions might be due to the formation of cesium telluride and selenide both compounds exhibit comparatively high vapor pressures (10- MPa at 1000 K, 0.1 MPa at 2000 K). 

Layton-Matthews, D., Leyboume, M.I., Peter, J.M., and Scott, S.D. (2006) Determination of selenium isotopic ratios by continuous-hydride-generation dynamic-reaction-cell inductively coupled plasma mass spectrometry. 

By using single-collector instruments equipped with a collision/reaction cell [248, 251] or double-focusing sector field instrumentation [248], it is possible to determine selenium isotope ratios at a precision and even accuracy of 0.2-0.5% RSD for most selenium isotope ratios. This level of performance can be considered sufficient for metabolic studies in humans and compares well with what can be achieved with NTIMS, although with much lower sample requirements. 

Elwaer, N. and Hintelmann, H. (2008) Comparing the precision of selenium isotope ratio measurements using collision cell and sector field inductively coupled plasma mass spectrometry. Talanta, 75, 205-214. 

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