Isotope analysis precision

Mass Spectrometry Bulletin (http //www.rsc.org/is/database/msbhome.htm) This is a current awareness bulletin providing information on mass spectrometry and related ion processes. The bulletin is sub-divided as follows instrument design and techniques isotopic analysis, precision mass measurement, isotope separation, age determination, etc. chemical analysis organic chemistry atomic and molecular processes surface phenomena and solid-state studies and thermodynamics and reaction kinetics. The database... 

O Neil, J.R., Roe, L.J., Reinhard, E. and Blake, R.E. 1994 A rapid and precise method of oxygen isotope analysis of biogenic phosphate. IsraelJournal of Earth Sciences 42 203-212. 

Accuracy for all thorium measurements by TIMS is limited by the absence of an appropriate normalization isotope ratio for internal correction of instrumental mass fractionation. However, external mass fractionation correction factors may be obtained via analysis of suitable thorium standards, such as the UC-Santa Cruz and IRMM standards (Raptis et al. 1998) for °Th/ Th, and these corrections are usually small but significant (< few %o/amu). For very high precision analysis, the inability to perform an internal mass fractionation correction is probably the major limitation of all of the methods for thorium isotope analysis discussed above. For this reason, MC-ICPMS techniques where various methods for external mass fractionation correction are available, provide improved accuracy and precision for Th isotope determinations (Luo et al. 1997 Pietruszka et al. 2002). 

Stirling CH, Lee DC, Christensen JM, Halliday AN (2000) High-precision in situ U-238-U-234-Th-230 isotopic analysis using laser ablation multiple-collector ICPMS. Geochim Cosmochim Acta 64 3737-3750... 

Applications The application of the isotope dilution technique is especially useful in carrying out precise and accurate micro and trace analyses. The most accurate results in mass spectrometry are obtained if the isotope dilution technique is applied (RSDs better than 1 % in trace analysis). Therefore, application of IDMS is especially recommended for calibration of other analytical data, and for certification of standard reference materials. The technique also finds application in the field of isotope geology, and is used in the nuclear industry for quantitative isotope analysis. 

Brenna J. T. (2001) Natural intramolecular isotope measurements in physiology elements of the case for an effort toward high precision position specific isotope analysis. Rapid Communications in Mass Spectrometry 15(15), 1252 1262. 

Tobias, H. J. and Brenna, J. T. (1997) On line pyrolysis as a limitless reduction source for high precision isotopic analysis of organic derived hydrogen. Analytical Chemistry 69, 3148 3152. 

Since about 1990, however, inductively coupled plasma (ICP, see Section 2.1.5) has become increasingly popular at the expense of TI in this area of application [9]. Although TI can provide better results for some analyses, ICP is more versatile and requires less sample preparation effort. Moreover, the advantage of better precision for TI is often compromised by the sample, for example, sample inhomogeneity. Nevertheless, there are still many examples where TI is used, such as for isotope analysis [10-13] and geochronology [14]. 

Compound-specific isotope analysis (CSIA) by GC-IRMS became possible in 1978 due to work of Mathews and Hayes [634], based on earlier low-precision work of Sano et al. [635]. The key innovation was the development of a catalytic combustion furnace based on Pt with CuO as oxygen source, placed between the GC exit and the mass spectrometer. The high pressure of helium (99.999% purity or better) ensures that all gas flows are viscous. After being dried in special traps avoiding formation of HC02 (i. e., interferes with 13C02) by ion-molecule reactions in the ion source, the C02 is transmitted to a device that regulates pressure and flow and then into the ion source [604]. 

The most widely used method for ionization is electron impact (El). In an El source the sample is placed in the path of an electron beam. Although many newer kinds of ion sources have been developed, El is the method commonly used in classical isotope-ratio mass spectrometers (IRMS), i.e. mass spectrometers designed for precise isotopic analysis. In this type of spectrometer the ions, once formed, are electrostatically accelerated, and then ejected through a slit into a magnetic field held perpendicular to the ion trajectory. In the magnetic sector part of the instrument the particles are deflected in an arc described by ... 

The relatively small mass differences for most of the elements discussed in this volume requires very high-precision analytical methods, and these are reviewed in Chapter 4 by Albarede and Beard (2004), where it is shown that precisions of 0.05 to 0.2 per mil (%o) are attainable for many isotopic systems. Isotopic analysis may be done using a variety of mass spectrometers, including so-called gas source and solid source mass spectrometers (also referred to as isotope ratio and thermal ionization mass spectrometers, respectively), and, importantly, MC-ICP-MS. Future advancements in instrumentation will include improvement in in situ isotopic analyses using ion microprobes (secondary ion mass spectrometry). Even a small increase in precision is likely to be critical for isotopic analysis of the intermediate- to high-mass elements where, for example, an increase in precision from 0.2 to 0.05%o could result in an increase in signal to noise ratio from 10 to 40. 

Corrections for instrumentally-produced mass fractionation that preserve natural mass dependent fractionation can be approached in one of two ways a double-spike method, which allows for rigorous calculation of instrumental mass fractionation (e.g., Dodson 1963 Compston and Oversby 1969 Eugster et al. 1969 Gale 1970 Hamelin et al. 1985 Galer 1999 see section Double-spike analysis ), or an empirical adjustment, based on comparison with isotopic analysis of standards (Dixon et al. 1993 Taylor et al. 1992 1993). The empirical approach assumes that standards and samples fractionate to the same degree during isotopic analysis, requiring carefully controlled analysis conditions. Such approaches are commonly used for Pb isotope work. However, it is important to stress that the precision and accuracy of isotope ratios determined on unknown samples may be very difficult to evaluate because each filament load in a TIMS analysis is different. 

Blichert-Toft J, Chauvel C, Albarede F (1997) Separation of Hf and Lu for high-precision isotope analysis of rock samples hy magnetic sector-multiple collector ICP-MS. Contrih Mineral Petrol 127 248-260 Cameron AE, Smith DH, Walker RL (1969) Mass spectrometry of nanogram-size samples of lead. Anal Chem 41 525-526... 

Dodson MH (1963) A theoretical study of the use of internal standards for precise isotopic analysis by the surface ionization technique Part I General first-order algebraic solutions. J Sci Instrum 40 289-295 Douglas DJ (1989) Some current perspectives on ICP-MS. Canad J Spectrosc 34 38-49 Douglas DJ, French JB (1986) An improved interface for inductively coupled plasma-mass spectrometry (ICP-MS). Spectrochim Acta 41B 197-204... 

Moriguti T, Nakamura E (1993) Precise lithium isotope analysis by thermal ionization mass spectrometry using lithium phosphate as an ion source. Proc Japan Acad Sci 69B 123-128 Moriguti T, Nakamura E (1998a) High-yield lithium separation and precise isotopic analysis for natural rock and aqueous samples. Chem Geol 145 91-104... 

Mason TFD, Weiss DJ, Horstwood M, Parrish RR, Russell SS, Mullane E, Coles BJ (2004b) High-precision Cu and Zn isotope analysis by plasma source mass spectrometry. Part 2. Correcting for mass discrimination effects. J Anal At Spectrom 19 218-226... 

The major analytical complication in Mo isotope analysis is precise correction for isotope fractionation during Mo purification and mass spectrometric analysis. This subject is reviewed in general by Albarede and Beard (2004), and is discussed here in particular reference to Mo. It is important to recognize that this challenge is fundamentally dififerent in mass dependent stable isotope studies as compared to investigations of mass-independent Mo isotope variations produced by nucleosynthesis. The latter have received attention in recent years for high-precision determination of Mo isotope composition (e.g., Dauphas et al. 2002a,b Yin et al. 2002), but are not relevant here. 

Samples were prepared for Cu isotope analysis on the Multicollector Inductively-Coupled Plasma Mass Spectrometer (MC-ICPMS) at University of Arizona. The Cu-rich samples were loaded and dissolved in pure HNO3 and the Cu-poor samples were loaded and dissolved in a mixture of HCI and HNO3, Chromatographic separation of the Fe and Cu ions was deemed necessary for the Cu-rich samples. The diluted solutions were injected into the MC-ICPMS using a microconcentric nebulizer. Samples were run numerous times to increase precision. The Cu isotope ratios are reported in conventional per mil notation, relative to the NIST 976 standard. Mass bias was also accounted for by bracketing methods with the NIST 976 standard. 

Beaudoin G, Taylor BE (1994) High precision and spatial resolution sulfur-isotope analysis using MILES laser microprobe, Geochim Cosmochim Acta 58 5055-5063 Beaudoin G, Taylor BE, Rumble D, Thiemens M (1994) Variations in the sulfur isotope composition of troUite from the Canyon Diablo iron meteorite, Geochim Cosmochim Acta 58 4253 255... 

Todt, W., Cliff, R.A., Hanser, A. and Hofmann, A.W., 1996. Evaluation of a Pb- Pb double spike for high-precision lead isotope analysis. In A.R. Basu, Hart, S. R. (Editor), Earth processes reading the isotopic code. Geophysical Monograph Am. Geophys. Union, pp. 429-437. 

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