MC-ICP

Raptis K, Mayer K, Hendrickx F, De Bievre P (1998) Preparation and certification of new thorium isotopic reference materials. Fresenius J Anal Chem 361 400-403 Rehkamper M, Halliday AN (1999) The precise measurement of T1 isotopic compositions by MC-ICP-MS Application to the analysis of geological materials and meteorites. Geochim Cosmochim Acta 63 935-944... 

This review highlights the important potential of U-series disequilibria in understanding the continental alteration and related mass transfers. The recent analytical developments, including TIMS and MC ICP MS techniques, for measuring small amounts of U, Th and Ra in geologic samples, offer today new possibilities and new perspectives for analysing U-series disequilibria in weathering profiles and river waters, and could lead to new and, as yet, unanticipated advances in the field of continental alteration. 

Multichannel analyzer (MCA), 26 434 Multichannel detection, in concentric hemispherical analyzers, 24 106 Multiclient studies, 15 635-636 Multicollector-I CP-MS (MC-ICP-MS), archaeological materials, 5 743 Multicolor displays, LEDs in, 22 175 Multicompartment drum filters, 11 357 Multicomponent copolymerization, 7 619-620... 

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 net effect of all this controversy was to stifle the application and development of what is, fundamentally, an extremely useful and practical technique. This is unfortunate, because in the last ten years advances in mass spectrometry, particularly the advent of high resolution MC-ICP mass... 

Figure 9.3 Schematic diagram of a multicollector ICP-MS (MC-ICP-MS). This is a double focusing instrument, with a hexapole (a six-rodded version of the quadropole) and a 90° magnetic selector, and a multiple bank of ion detectors, allowing simultaneous measurement of a number of isotopic ratios.

These comments apply to the running of a low resolution quadrupole ICP-MS, capable of both solution and laser ablation analysis, since this is the most widespread form of the instrument. High resolution MC ICP-MS is, as they say, a whole other ball game ... 

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. 

The MC-ICP-MS consists of four main parts 1) a sample introduction system that inlets the sample into the instrument as either a liquid (most common), gas, or solid (e.g., laser ablation), 2) an inductively coupled Ar plasma in which the sample is evaporated, vaporized, atomized, and ionized, 3) an ion transfer mechanism (the mass spectrometer interface) that separates the atmospheric pressure of the plasma from the vacuum of the analyzer, and 4) a mass analyzer that deals with the ion kinetic energy spread and produces a mass spectrum with flat topped peaks suitable for isotope ratio measurements. 

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 5. The inductively-coupled plasma source (inspired by Niu and Houk 1996). The original figure has been modified to show the electrical potentials, the vacuum cascade (top), and the distribution of ions and neutral (bottom) in an MC-ICP-MS similar to the VG Plasma 54. The zone with incipient voltage acceleration right behind the skimmer show maximum space-charge effect with the lighter ions being most efficiently driven off by the strong axial current of positive ions.

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. 

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

Weyer S, Schwieters JB (2003) High precision Fe isotope measurements with high mass resolution MC-ICP-MS. Int J Mass Spectrom 226 355-368... 

Woodhead J (2002) A simple method for obtaining highly accurate Pb isotope data by MC-ICP-MS. J Anal At Spectrom 17 1381-1385... 

The recent and meteoric development of plasma source mass spectrometers equipped with high stability sector-field magnets and multiple collectors (MC-ICP-MS) has lead to a... 

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