Mass spectrometry, accelerator

Note Mass spectral imaging creates sort of a chemical map filled with enormous amounts of data. A standard image of 256 x 256 pixels requires 65,536 mass spectra each possessing about 10 data points. Therefore, effective software tools for data evaluation, representation, and eventually compression for long-term storage are necessary to deal with those gigabytes of data 

The methodology of accelerator mass spectrometry (AMS) clearly differs from all other approaches to analyzing of atomic mass so far referred to in this book. While ions to be analyzed by a quadmpole analyzer are injected at kinetic energies of about 10 eV, those for a sector instrument at 5-10 keV, and those for TOFs at 15-30 keV, in AMS ions have several MeV. Another unique and key feature of the technique is that the ions experience dramatic changes in kinetic energy and charge state during the experiment. 

AMS is an extremely sensitive technique for isotopic analysis, in particular for measuring isotope ratios over an extreme dynamic range. For some elements such as carbon, isotope ratios of as low as 1 in 10 can be determined. This is by a fac- 

Example To illustrate the capabihties of AMS, we compare carbon-14 determination by radioactive counting to AMS. A sanple of 1 g of environmental carbon contains 6 x 10 atoms of (and 1.2 x 10 times more atoms). Due to the 5730 years half-life of C, only 13 atoms will decay per minute. For a statistical precision of 0.5% as normally required in radiocarbon dating, decays from 1 g of carbon need to be counted for more than 48 h. AMS does not have to wait for the decays, it is more efficient because it uses the whole sanple. A sample of 1 mg carbon, only one thousandth of the material needed for decay counting, is completely sputtered in the ion source within 1-2 h and delivers about 6 x 10 atoms, which is 1% of the total content, to the AMS detector system Conventional mass spectrometers can not be used here, because the ions are superimposed by atomic and molecular isobars that are by orders of magnitude more abundant. These are and small fragments such as and Li2. Ab- 

While working as a mass spectrometrist is necessarily correlated to a certain field of personal expertise, one should also be aware - at least to the degree of a good educational background in mass spectrometry - of the entire spectrum of this impressingly versatile method - mass spectrometry, a domain of science in itself. 

An accelerator mass spectrometer is not really just an instrument with another type of analyzer, but rather a system that utilizes magnetic/electric sectors to separate ion species. In fact, it can also be looked upon as an ion source. However, we felt it belonged best among the analyzers, because of the way it is utilized. 

The measurement is always relative, that is, in 14C measurements the amount of 14C is always related to that of 13C or 12C. The more abundant isotope is detected by a Faraday detector while the less abundant isotope is detected by a specialized device 

Why then, is such a complicated and expensive set up necessary AMS combines mass spectrometric features with efficient discrimination of isobaric and molecular interferences. Therefore, it can detect and quantify atomic species of very low abundance. In the case of 14C dating, before AMS was utilized, about 1 g of carbon was needed to date an archaeological item. One gram of fresh carbon contains about 6 x 1010 14C atoms, of which 14 decay per minute. To get 0.5% statistical precision using decay counting, a 48 h acquisition time is necessary. The same result can be obtained with AMS in about 10 min and with only 1 mg of carbon. 

Performance Parameters. Since the detector is often involved in the separation of isobars, normal mass analyzer resolution and mass accuracy do not really apply. The mass spectrometric resolution would be determined by the magnetic and electric sectors. Only atomic species are analyzed, so that sets the upper m/z 

Analysis time is typically of the order of minutes to hours depending on the sample. Normally the time spent in actual AMS analysis is not the constraining factor, but rather sample purification prior to the spectrometric analysis. Accelerator mass spectrometers are space demanding facilities that typically occupy hundreds of square meters. Normally, dedicated personnel operate the device. Considerable effort is directed into refining the methods to allow operation by smaller, less costly facilities. 

For the direct analysis of in biological species, an interface is available [43]. The liquid samples are deposited into a bed of CuO powder which is held on a refractory support in an enclosed chamber. The CuO matrix is heated locally by an infrared laser, and the CO2 evolved is swept away by a flow of He into the ion source. 

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Tuniz, C., Accelerator Mass Spectrometry Ultrasensitive Analysis for Global Science, CRC Press, Boca Raton, FL, 1998. 

Neutron activation also has been combined with accelerator mass spectrometry and has been demonstrated to have part-per-billion sensitivities fer bulk nitrogen analysis in silicon. This combination was also used to obtain depth profile of Cl in silicon semiconductors. ... 

Gillespie, R., Hedges, R.E.M. and Wand, J.O. 1984 Radiocarbon dating of bone by Accelerator Mass Spectrometry. Journal of Archaeological Science 11 165-170. 

Le Vuong, T. et al.. Phytochemical research using accelerator mass spectrometry, Nutr. Rev., 62, 375, 2004. 

Dueker, S.R. et al.. Long-term kinetic smdy of P-carotene, using accelerator mass spectrometry in an adult volunteer, J. Lipid Res., 41, 1790, 2000. 

Soon after this discovery the harnessing of the technique to the measurement of all the U isotopes and all the Th isotopes with great precision immediately opened up the entire field of uranium and thorium decay chain studies. This area of study was formerly the poaching ground for radioactive measurements alone but now became part of the wonderful world of mass spectrometric measurements. (The same transformation took place for radiocarbon from the various radioactive counting schemes to accelerator mass spectrometry.)... 

Accelerator mass spectrometry Acousto-optical tuneable filter Acousto-optical tuneable spectrometer/scanning Atom probe... 

A more recently developed technique, known as the accelerator mass spectrometry (AMS) radiocarbon dating technique, based on counting, in a mass spectrometer, the relative amount of radiocarbon to stable carbon isotopes in a sample (see Textbox 10). 

AMS 14C dating Abbreviation for accelerator mass spectrometry radiocarbon dating. AMU Acronym for atomic mass unit. 

Gove, H. E. (1999), From Hiroshima to the Iceman The Development and Applications of Accelerator Mass Spectrometry, Institute of Physics, Bristol. 

Harris, D. R. (1987), The impact on archaeology of radiocarbon dating by accelerator mass spectrometry, Phil. Trans. Roy. Soc. A323, 23-43. 

Valladas, H. (2003), Direct radiocarbon dating of prehistoric cave paintings by accelerator mass spectrometry, Meas. Sci. Technol. 14, 1487-1492. 

R. C. Garner, J. V. Garner, S. Gregory, M. Whattam, A. Calam, D. Leong. Comparison of the absorption of micronized (daflon 500 mg) and nonmicronized 14C-diosmin tablets after oral administration to healthy volunteers by accelerator mass spectrometry and liquid scintillation counting. J. Pharm. Sci. 2002, 91, 32— 40. 

The impact of this new technique, which was called Accelerator Mass Spectrometry (AMS), on the radiocarbon and archaeologist communities, was immediate and revolutionary. The introduction of AMS is indeed recognized by some as the third revolution in radiocarbon dating[22,23] and it has provided the opportunity to date very precious finds by collecting very small samples. The interest in developing the technique of AMS was so evident that, just few years after the measurements cited above, a first dedicated AMS system (based on a tandem accelerator) was designed and built [24] then, the first dedicated... 

C. Tuniz, Accelerator mass spectrometry ultra sensitive analysis for global science, Rad. Phys. Chem. 61, 317 322 (2001). 

R. Middleton, A review of ion sources for accelerator mass spectrometry, Nucl.Instrum. Methods B 5, 193 199 (1984). 

A. E. Litherland and L. R. Kilius, A recombinator for radiocarbon accelerator mass spectrometry, Nucl. Instrum. Methods B 52, 375 377 (1990). 

R.J. Schneider, K.F. von Reden and K.H. Purser, A triple isotope injector for accelerator mass spectrometry, Particle Accelerator Conference, 1991, Accelerator Science and Technology, Conference Record of the 1991 IEEE, 878 880 (1991). 

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