Spectrometry, mass isotopic fractionation

Within this chapter, we focus on four elements (C, O, N, S), which participate in most marine geochemical reactions and which are important elements in the biological system. Some recent developments in the use of B isotopes are added to this chapter. We summarize the influence of geochemical processes on the stable isotope distribution of those elements in ocean water and marine sediments. After a short review on the fundamentals of stable isotope fractionation and mass spectrometry, the most important fractionation mechanisms for each el-... 

To determine if there is significant mass fractionation occurring during exposure of the sample to oxygen plasmas, the values of CO2 produced from successive oxygen plasmas were compared, both for internal consistency and with values of bulk material (when available). All measurements here were determined by conventional stable isotope mass spectrometry. The means and sample standard deviations (s), along with the standard errors of the means (Sm shown in parentheses) are reported in Table II. Q-tests at 95% confidence levels were performed on all measurements taken here no measurements were rejected. 

For precise measurement of isotopic composition by mass spectrometry, it is also common to use either a natural, known isotopic ratio to correct for instrumental mass fractionation (e g., internal normalization) or to add a tracer for this purpose. For example for natural uranium samples, one can use the natural U/ U of 137.88 to correct for fractionation. Alternatively, one can use an added double spike of ratio -unity... 

Gunther D, Heimich CA (1999) Enhanced sensitivity in laser ablation-ICP mass spectrometry using helium-argon mixtures as aerosol carrier. J Anal At Spectrom 14 1363-1368 Habfast K (1998) Fractionation correction and multiple collectors in thermal ionization isotope ratio mass spectrometry. Inti J Mass Spectrom 176 133-148... 

Figure 3.2. Stable isotope labeling for quantifying differential protein expression. Cell populations are grown in either 14N or 15N containing medium. Protein lysates are fractionated and separated by 2D gel electrophoresis. Protein spots are excised, digested with trypsin and the mass of the resulting peptides is determined by mass spectrometry. The presence of 15N results in a shift and creates two peaks for each peptide. The ratio of intensities of the peaks is indicative of the relative expression levels of the proteins. Spot A contains a protein that is expressed at similar levels in both cell pools. Spot B contains a protein that is expressed at higher levels in cell pool 2. Figure adapted from Oda et al. (1999).

Bostrom B, Comstedt D, Ekblad A (2008) Can isotopic fractionation during respiration explain the 13C enriched sporocarps of ectomycorrhizal and saprotrophic fungi New Phytol 177 1012-1019 Boutton TW (1996) Stable carbon isotopes ratios of soil organic matter and their use as indicators of vegetation and climate change. In Boutton TW, Yamasaki S (eds) Mass spectrometry of soils. Marcel Dekker Inc., New York, pp 47-82... 

Carlson RW, Hauri EH, Alexander CMO D (2001) Matrix induced isotopic mass fractionation in the ICP-MS. In Plasma source mass spectrometry The new Millennium. Holand G, Turner SD (eds), Cambridge Roy Soc Chem, p 288-297... 

Habfast K (1998) Fractionation correction and multiple collectors in thermal ionization isotope ratio mass spectrometry. Int J Mass Spec 176 133-148... 

Jackson SE, Gunther D (2003) The nature and sources of laser induced isotopic fractionation in laser ablation-multicollector-inductively coupled plasma-mass spectrometry. J Anal At Spectrom 18 205-212 Jiang S-J, Houk RS, Stevens MA (1988) Alleviation of overlap interferences for determination of potassium isotope ratios by Inductively-Coupled Plasma Mass Spectrometry. Anal Chem 60 1217-1220 Lam JWH, Horlick G (1990) A comparison of argon and mixed gas plasmas for inductively coupled plasma-mass spectrometry. Spectrochim Acta Part B 45 1313-1325 Langmuir I, Kingdon KH(1925) Thermionic effects caused by vapours of alkali metals. Phil Trans R Soc A107 61-79... 

Rameback H, Berglund M, Kessel R, Wellum R (2002) Modeling isotope fractionation in thermal ionization mass spectrometry filaments having diffusion controlled emission. Int J Mass Spectrom 216 203-208 Roe JE, Anhar AD, Barling J (2003) Nonhiological fractionation of Fe isotopes evidence of an equilibrium isotope effect. Chem Geol 195 69-85... 

Russel WA, Papanastassiou DA, Tomhrello TA (1978) Ca isotope fractionation on the Earth and other solar system materials. Geochim Cosmochim Acta 42 1075-1090 Sakata KI, Kawahata K (1994) Reduction of fundamental polyatomic ions in inductively coupled plasma mass spectrometry. Spectrochim Acta Atom Spectrosc PartB 49 1027-1038 Siehert, C, Nagler, TF, Kramers JD (2001) Determination of molybdenum isotope fractionation by doublespike multicollector inductively coupled plasma mass spectrometry. Geochem Geophys Geosyst 2 2000GC000124... 

Franklin et al. 1986). None of these techniques has enjoyed long term success. Measurement of Li isotopes by mass spectrometry faces the primary problem of controlling mass fractionation from the emitter. Ironically, the very property that makes Li geochemically interesting makes quantifying its isotopic composition with precision extraordinarily challenging. For this reason, mass spectrometric measurements of Li must be compared directly to a standard material. As long as all laboratories make use of the same standard material, its isotopic composition is academic, as the measured isotopic composition of the standard drops out of the arithmetic of normalization. 

Layne GD (2003) Advantages of secondary ion mass spectrometry (SIMS) for stable isotope microanalysis of the trace light elements. EOS Trans, Am Geophys Union 84 F1635 Lundstrom CC, Chaussidon M, Kelemen P (2001) A Li isotope profile in a dunite to Iherzolite transed within the Trinity Ophiolite evidence for isotopic fractionation by diffusion. EOS Trans, Am Geophys Union 82 991... 

With the advent of multiple-collector inductively coupled plasma-source mass spectrometry (MC-ICPMS) it is now possible to measure Mg/ Mg and Mg/ Mg of Mg in solution with a reproducibility of 30 to 60 ppm or better (Galy et al. 2001). What is more, ultraviolet (UV) laser ablation combined with MC-ICPMS permits in situ analysis of Mg-bearing mineral samples with reproducibility of 100 to 200 ppm (Yoimg et al. 2002a). These new analytical capabilities allow mass-dependent fractionations of the isotopes of Mg to be used as tracers in natural systems. 

CAI s that were once molten (type B and compact type A) apparently crystallized under conditions where both partial pressures and total pressures were low because they exhibit marked fractionation of Mg isotopes relative to chondritic isotope ratios. But much remains to be learned from the distribution of this fractionation. Models and laboratory experiments indicate that Mg, O, and Si should fractionate to different degrees in a CAI (Davis et al. 1990 Richter et al. 2002) commensurate with the different equilibrium vapor pressures of Mg, SiO and other O-bearing species. Only now, with the advent of more precise mass spectrometry and sampling techniques, is it possible to search for these differences. Also, models prediet that there should be variations in isotope ratios with growth direction and Mg/Al content in minerals like melilite. Identification of such trends would verify the validity of the theory. Conversely, if no correlations between position, mineral composition, and Mg, Si, and O isotopic composition are found in once molten CAIs, it implies that the objects acquired their isotopic signals prior to final crystallization. Evidence of this nature could be used to determine which objects were melted more than once. 

Newton R, Aranovich L (1996) Simple granulite melting in concentrated NaCl-KCl solutions at deep crustal conditions. Geol Soc Am Annu Meet Abstracts with Programs 158 Numata M, Nakamura N, Koshikawa H, Terashima Y (2002) Chlorine isotope fractionation during reductive dechlorination of chlorinated ethenes by anaerobic bacteria. Env Sci Tech 36(20) 4389-4394 Numata M, Nakamura N, Gamo T (2001) Precise measurement of chlorine stable isotopic ratios by thermal ionization mass spectrometry. Geochem J 35(2) 89-100 Owen HR, Schaeffer OA (1995) The isotope abundances of chlorine from various sources. J Am Chem Soc 77 898-899... 

Gussone N, Eisenhauer A, Heuser A, Dietzel M, Bock B, Bohm E, Spero H, Lea D, Buma J, Nagler, TF (2003) Model for kinetic effects on calcium isotope fractionation (6 Ca) in inorganic aragonite and cultured planktonic foraminifera. Geochim Cosmochim Acta 67 1375-1382 Halicz L, Galy A, Belshaw NS, O Nions RK (1999) High precision measurement of calcium isotopes in carbonates and related materials by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). J Anal Atom Spectr 14 1835-1838... 

Ireland TR, Fahey AJ, Zinner EK (1991) Hibonite-bearing microspherules a new type of refractory inclusions with large isotopic anomalies. Geochim Cosmochim Acta 55 367-379 Johnson CM, Beard BL (1999) Correction of instrumentally produced mass fractionation during isotopic analysis of Fe by thermal ionization mass spectrometry. Int J Mass Spect 193 87-99 Jungck MHA, Shimamura T, Lugmair GW (1984) Calcium isotope variations in Allende. Geochim Cosmochim Acta 48 2651-2658... 

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