MC-ICP-MS use

Vance D, Thirlwall ME (2002) An assessment of mass discrimination in MC-ICP-MS using Nd isotopes. Chem Geol 185 227-240... 

Further applications of LA-MC-ICP-MS using the Plasma 54 by Zr isotope ratio measurements in zircon and baddeleyite samples are described by Hirata.147 The isotope ratios 92Zr/90Zr = 0.333 94 0.000 02 and 96Zr/90Zr = 0.054 63 0.000 01 have been determined on a Merck reagent with a precision of 0.01-0.02% and 0.03-0.04%, respectively. Neither isotopic variation in the... 

FIGURE 31.6 Schematic diagram showing the structure of the Neptune MC-ICP-MS used for U-Pb zircon geochronology. 

The Re and Os concentrations of the shales are variable, between 0.3-1500 ng kg for Re and 0.04—1.2 ng kg for Os, with Re/ Os ratios of 50-1000 [117-120]. Again, the small amounts of Os makes it more difficult to carry out the analysis by MC-ICP-MS using Faraday cups, but the rather high Os/ Os ratios make it possible to obtain meaningfid ages with single-collector ICP-MS [119]. 

Hartlaub, R.P., Greaser, R.A., MacHattie, T.G., and Bohm, C. (2005) U-Pb zircon dating by laser ablation-MC-ICP-MS using a new multiple ion counting Faraday collector array. 

Tipper, F.T., Louvat, P., Capmas, F., Galy, A., and Gaillardet, J. (2008) Accuracy of stable Mg and Ca isotope data obtained by MC-ICP-MS using the standard addition method. Chem. Geol, 257, 65-75. 

N., Bock, B., Liebetrau, V., Nagler, T., Spero, H.J., Bijma. J., and Dullo, C. (2004) Direct measurement of C3ij" °C3L ratios by MC-ICP-MS using the cool plasma technique. Chem. Geol., 206, 11-20. 

Simultaneous acquisition of aU relevant Yb, Lu and Hf isotopes is possible in MC-ICP-MS using a static acquisition protocol similar to the one shown below. 

Clayton, R., Andersson, P., Gale, N.H., Gillis, C. and Whitehouse, MJ. (2002). Precise determination of the isotopic composition of Sn using MC-ICP-MS. Journal of Analytical Atomic Spectrometry 17 1248-1256. 

Ponting, M., Evans, J.A and Pashley, V. (2003). Fingerprinting of Roman mints using laser-ablation MC-ICP-MS lead isotope analysis. Archaeometry 45 591-597. 

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. 

Figure 3. Fassel type torch that is typically used in MC-ICP-MS. Approximate Ar flow rates for the different plasma gasses are shown and the relative spatial relationships between the intermediate and sample lines relative to the RF-coil where the Ar plasma is generated are shown.

Figure 14. Plot of difference of the 6 Fe value of an Fe standard that was partially reduced minus the 6 Fe value of an Fe standard that was partially oxidized versus the relative oxidation state of the standard as determined colorimetrically using 2,2 -hipyridine. Data from Zhu et al. (2002) collected using an Nu-Plasma MC-ICP-MS.

In principle, double-spike techniques represent the most suitable approach to determine the isotope composition of elements with four isotopes or more (Fe, Zn). In most cases, these techniques involve the addition of an isotope which is usually minor in natural samples, such as Zn or Fe, implying that the risk introduced by memory effects on these spike isotopes must be carefully weighed against the added gain in precision from using the double spike. Such a risk is clearly more present with MC-ICP-MS than with TIMS. 

As the L-SVEC standard is ordinarily analyzed frequently among sample analyses by MC-ICP-MS, it is not useful to use this measurement rmcertainty to estimate analytical precision (Tomascak et al. 1999a), but rather the reproducibility of independent measurements of samples in replicate or duplicate can be used. Parameters of accuracy and precision are discussed below. 

External precision is the ability to demonstrate analytical repeatability with multiple preparations and analyses of a material over a long period of time. The MC-ICP-MS techniques and the more widespread TIMS methods either demonstrate or claim external precisions in the range 0.5 to 1.0%o (2ct). The stated precision for most TIMS methods is estimated from the reproducibility of the L-SVEC standard. In many cases the analysis of individual samples prepared multiple times yields precisions poorer than this estimate. This is in part due to the heterogeneity of natural samples and in part due to effects introduced during preparation and analysis that are not experienced by the standard. Zhang et al. (1998) cite reproducibility of the L-SVEC standard of <1.0%o (2ct), but their duplicate measurements of individual pore water samples vary from 0.1 %o to 6.1 %o (mean 2.3%o all 2cj). Later studies using refined TIMS procedures appear to achieve superior replicate precision (e.g., 0.4%o to 1. l%o for multiple replicates in Chan et al. 2002c). 

A double spike technique is essential for TIMS analyses of Se and Cr, and may also be useful in MC-ICP-MS analysis. Briefly, two spike isotopes with a known ratio are added to each sample, and the measured ratio of the spike isotopes is used to determine and correct for instrumental bias. Examples of Se and Cr double spikes currently in use are given in Table 1. The fact that small amounts of the spike isotopes are present in the samples and small amormts of nominally unspiked isotopes are found in the spikes is not a problem, as the measurements allow highly precise mathematical separation of spike from samples. Algorithms for such calculations are described by Albarede and Beard (2004) and, specifically for Se, by Johnson etal. (1999). 

Gas-source mass spectrometry. Work on Se stable isotopes has a long history, dating back to the Ph.D. work of H. Roy Krouse around 1960. From 1960 to 1990, analyses were done by gas-source mass spectrometry using SeF (Krouse and Thode 1962). The sample Se was converted to Se(0), then reacted with Fj gas to produce SeF. This method required large quantities (e.g., tens of micrograms) of Se for measurements and thus was not widely applied. Recent continuous flow mass spectrometry methods could enable gas-source measurements on much smaller quantities, but will still use too much sample to compete with TIMS and MC-ICP-MS methods. 

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