Mass spectrometry particle measurements using

Figure 6.12 Mass spectra for two particles measured using time oFnighi mass spectrometry in a laboratory at the Technical University of Delft in The Netherlands (Weiss et al 1997). The lop spectrum probably comes from a particle of marine origin and the bottom from a local source with construction material components.

Uranium-233 (V, = -1.59 10 years) is formed through neutron capture by Th (mainly in thorium-fueled nuclear reactors) followed by emission of two beta particles. Alternatively, may be formed by alpha decay of Np that in turn is produced through a sequence of nuclear reactions in uranium-fueled reactors. The °Th decay product of is the relatively short-lived (t = -7880 years) so the ratio between these nuclides is linear for thousands of years after purifications. Alpha spectrometry and mass spectrometry can be used for measuring the Th/ U ratio. In special cases, this pair of nuclides cau serve as a chrouometer for nuclear proliferation, particularly if fissile is produced in reactors fueled with thorium. 

One is compelled to pose the question if experimentally it will become possible to decide whether the 14C variations observed on tree-ring samples, peat bogs, sediments, etc., are primarily caused by an external forcing of the system (production rate variations) or by an internal one. Recent progress in detection of small numbers of nuclei of an isotope by mass spectrometry based on the use of a particle accelerator [57,58] make it possible to measure the cosmic ray produced 10Be or 36C1 deposited in only 1 kg of ice. These isotopes get attached to aerosol particles and deposited with them. 

As seen in Chapter 9.C.2, a very wide variety of organics are found in particles in ambient air and in laboratory model systems. The most common means of identification and measurement of these species is mass spectrometiy (MS), combined with either thermal separation or solvent extraction and gas chromatographic separation combined with mass spectrometry and/or flame ionization detection. For larger, low-volatility organics, high-performance liquid chromatography (HPLC) is used, combined with various detectors such as absorption, fluorescence, and mass spectrometry. For applications of HPLC to the separation, detection, and measurement of polycyclic aromatic hydrocarbons, see Wingen et al. (1998) and references therein. 

Other modifications to the reaction conditions of the Brust-Schiffrin method, such as a reduction temperature of — 78 °C and the use of a hyperexcess of hexanethiol, results in an Au38(thiolate)24, based on observations, LDI-TOF mass spectrometry, TGA analysis and elemental analysis [69]. The influence of preparation temperature on the size and monodispersity of dodecylthiol monolayer protected gold clusters has also been reported. Both and SAXS measurements show that higher temperatures increase polydispersity. This modification of poly-dispersity may be related to the existence of a dynamic exchange of thiols at the particle surface with thiols in the solvent [70]. 

Acceleration mass spectrometry (AMS) - The precise measurement of isotopic ratios for very low abundance isotopes is beyond the capability of conventional mass spectrometers. In these cases of isotopes at minute trace levels, some 50 mass spectrometers exist worldwide. The tendetrons used for these types of analyses are derived from Van de Graaff-type particle accelerators. These instruments are based on tandem mass spectrometry. 

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The homogeneity of this binary layer composition was examined using secondary neutral particles mass spectrometry (SNMS) [37]. This procedure removes the catalyst coat stepwise and delivers the amount of the catalyst components in the respective layer depending on the sputtering time. One second of sputtering time corresponds here to a layer removal of approximately 1 nm. Hence the sputtering time is also a measure of the layer thickness. The maximum layer thickness was 500 nm. 

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