Clusters mass spectrometry

Harden T.C. Imeson, Detection and Identification of Trace Quantities of Organic Vapors in the Atmosphere by Ion Cluster Mass Spectrometry and the Ionization Detector System ,... 

Although gas phase clusters can be generated by a number of techniques, adiabatic expansions are the most widely utilized method for the generation of vdW clusters. A wealth of information regarding the energetics, dynamics, and structures of clusters has been recently obtained due to the availability of many new and improved experimental techniques. Although a number of spectroscopic techniques have been utilized in investigating vdW clusters, mass spectrometry (MS) is extensively employed for the study of clusters, as it enables size selective... 

Winograd, N., Garrison, B.J. (2010) Biological cluster mass spectrometry. Anna. Rev. Phys. Chem., 61, 305-322. 

The hydration of more inert ions has been studied by O labelling mass spectrometry. 0-emiched water is used, and an equilibrium between the solvent and the hydration around the central ion is first attained, after which the cation is extracted rapidly and analysed. The method essentially reveals the number of oxygen atoms that exchange slowly on the timescale of the extraction, and has been used to establish the existence of the stable [1 10304] cluster in aqueous solution. 

Castleman A W and Mark T D 1986 Cluster ions their formation, properties, and role in eluoidating the properties of matter in the oondensed state Gaseous Ion Chemistry and Mass Spectrometry ed J FI Futrell (New York Wiley)... 

Schlager H and Arnold F 1985 Balloon-borne fragment ion mass spectrometry studies of stratospheric positive ions unambiguous detection of H (CH3CN), (H20)-clusters Pianet. Space Sc/. 33 1363-6... 

There are otlier teclmiques for mass separation such as tire quadmpole mass filter and Wien filter. Anotlier mass spectrometry teclmique is based on ion chromatography, which is also capable of measuring tire shapes of clusters [30, 31]. In tills metliod, cluster ions of a given mass are injected into a drift tube witli well-defined entrance and exit slits and filled witli an inert gas. The clusters drift tlirough tills tube under a weak electric potential. Since the... 

Lover T efa/1997 Electrospray mass spectrometry of thiophenolate-capped clusters of CdS, CdSe and ZnS and cadmium and zinc thiophenolate complexes observation of fragmentation and metal, chalcogenide and ligand exchange processes Inorg. Chem. 36 3711... 

Isopropyl group (Section 2 13) The group (CH3)2CH— Isotactic polymer (Section 7 15) A stereoregular polymer in which the substituent at each successive chirality center is on the same side of the zigzag carbon chain Isotopic cluster (Section 13 22) In mass spectrometry a group of peaks that differ in m/z because they incorporate differ ent isotopes of their component elements lUPAC nomenclature (Section 2 11) The most widely used method of naming organic compounds It uses a set of rules proposed and periodically revised by the International Union of Pure and Applied Chemistry... 

Laser-desorption mass spectrometry (LDMS) or matrix-assisted laser desorption ionization (MALDI) coupled to a time-of-flight analyzer produces protonated or deprotonated molecular ion clusters for peptides and proteins up to masses of several thousand. 

Mass spectral analysis of quaternary ammonium compounds can be achieved by fast-atom bombardment (fab) ms (189,190). This technique rehes on bombarding a solution of the molecule, usually in glycerol [56-81-5] or y -nitroben2yl alcohol [619-25-0], with argon and detecting the parent cation plus a proton (MH ). A more recent technique has been reported (191), in which information on the stmcture of the quaternary compounds is obtained indirectly through cluster-ion formation detected via Hquid secondary ion mass spectrometry (Isims) experiments. 

In Secondary Ion Mass Spectrometry (SIMS), a solid specimen, placed in a vacuum, is bombarded with a narrow beam of ions, called primary ions, that are suffi-ciendy energedc to cause ejection (sputtering) of atoms and small clusters of atoms from the bombarded region. Some of the atoms and atomic clusters are ejected as ions, called secondary ions. The secondary ions are subsequently accelerated into a mass spectrometer, where they are separated according to their mass-to-charge ratio and counted. The relative quantities of the measured secondary ions are converted to concentrations, by comparison with standards, to reveal the composition and trace impurity content of the specimen as a function of sputtering dme (depth). 

Key Words —Fullerenes, mass spectrometry, clusters, eieclroiiic shells, icosahedral layers. 

Isotopic cluster (Section 13.22) In mass spectrometry, a group of peaks that differ in mh because they incorporate different isotopes of their component elements. 

The control of materials purity and of environmental conditions requires to implement physico-chemical analysis tools like ESC A, RBS, AUGER, SEM, XTM, SIMS or others. The principle of SIMS (Secondary Ion Mass Spectroscopy) is shown in Eig. 31 an ion gun projects common ions (like 0+, Ar+, Cs+, Ga+,. ..) onto the sample to analyze. In the same time a flood gun projects an electron beam on the sample to neutralize the clusters. The sample surface ejects electrons, which are detected with a scintillator, and secondary ions which are detected by mass spectrometry with a magnetic quadrupole. 

There are several methods in use for producing these clusters. Particle bombardment or laser vaporization of a graphite surface leads to direct formation of ions that can be detected by mass spectrometry. These are normally of relatively small size (n<30). By laser vaporization of graphite into a molecular beam neutral... 

Secondary ion mass spectrometry (SIMS) is by far the most sensitive surface technique, but also the most difficult to quantify. When a surface is exposed to a beam of ions (Ar", 0.5-5 keV), energy is deposited in the surface region of the sample by a collisional cascade. Some of the energy will return to the surface and stimulate the ejection (desorption) of atoms, ions, and multi-atomic clusters. In SIMS, positive or negative secondary ions are detected directly with a quadrupole mass spectrometer. 

In order to dissolve ionic solutes so readily, water molecules must solvate the ions as they enter solution. Consequently, water molecules lose their translational degrees of freedom as a result of their association with specific ions. It is possible to estimate the number of water molecules in clusters of the type (H20) using mass spectrometry (Kebarle, 1977). 

When water undergoes self-ionization, a range of cationic species are formed, the simplest of which is the hydronium ion, HjO (Clever, 1963). This ion has been detected experimentally by a range of techniques including mass spectrometry (Cunningham, Payzant Kebarle, 1972), as have ions of the type H+ (HaO) with values of n up to 8. Monte-Carlo calculations show that HjO ions exist in hydrated clusters surrounded by three or four water molecules in the hydration shell (Kochanski, 1985). These ions have only a short lifetime, since the proton is highly mobile and may be readily transferred from one water molecule to another. The time taken for such a transfer is typically of the order of 10 s provided that the receiving molecule of water is correctly oriented. 

The chemical compositions of the isolated Au SR clusters were investigated by mass spectrometry [15,16,18, 22,32-35]. TEM was used to confirm that the species detected by the mass spectrometer represents the clusters in the sample. Figure 3a is a schematic representation of the top view of the mass spectrometer, which consists of five stages of differentially pumped vacuum chambers. The apparatus accommodates two t5 pes of ion sources, electrospray ionization (ESI) and laser-desorption ionization (EDI), and a time-of-flight (TOE) mass spectrometer with a reflectron. Details of the apparatus and the measurement protocols are described below. 

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