Mass spectra transition metals

Similar experiments on a large number of transition metal carbonyls have shown that this process favors dissociation to and detection of metal clusters or atoms. Since most metal-(CO)n photofragments are themselves subject to efficient dissociation, MPI experiments do not identify the primary photoproducts. This situation contrasts sharply with electron impact ionization where the parent ion is usually formed and daughter ions are seen as a result of parent ion fragmentation. Figure 4 shows the electron impact mass spectrum of Mn2(C0) Q (33). for comparison with the MPI mass spectrum of Figure 3. 

MALDI is the method of choice for the analysis of synthetic polymers because it usually provides solely intact and singly charged [62] quasimolecular ions over an essentially unlimited mass range. [22,23] While polar polymers such as poly(methylmethacrylate) (PMMA), [83,120] polyethylene glycol (PEG), [120,121] and others [79,122,123] readily form [M+H] or [M+alkali] ions, nonpolar polymers like polystyrene (PS) [99,100,105,106] or non-functionalized polymers like polyethylene (PE) [102,103] can only be cationized by transition metal ions in their l-t oxidation state. [99,100] The formation of evenly spaced oligomer ion series can also be employed to establish an internal mass calibration of a spectrum. [122]... 

In some polynuclear metal carbonyls of the first row (3d) transition metals the metal-metal bonds are too weak to survive complete loss of carbonyl groups. Thus in the mass spectrum of Fe3(CO)i2 stepwise loss of carbonyl groups occurs only as far as the tricarbonyltriiron ion Fe3(C0)s 2fl>. The rupture of the iron-iron bonds competes with the stepwise loss of carbonyl groups givingions such as Fe2(CO)4 and Fe(CO)4. The mass spectrum of Fe2(CO)9 exhibits the ion Fe(CO) which may represent pentacarbonyliron formed by the following pyrolysis process25) ... 

The transition-metal allyl complexes are air- and temperature-sensitive solids Cr(allyl)3, m.p. ca. 70° Ni(allyl)2, m.p. ca. 0°. The infrared spectrum of both compounds indicates that the bonding of the allyl group to the metal involves r electrons (the olefinic bond appearing at 1520 and 1493 cm.-1, respectively) they can be identified by their mass spectra. 

Elements with distinctive isotope ratios (Cl, Br, and transition metals, for example) will provide a distinctive isotopic cluster in the mass spectrum of a compound. This can be used to identify the presence of elements within unknown compounds. 

Chelation of copper with tetraphenylporphyrin was first reported as a technique for measuring copper in rat brain by isotope dilution O) This method appeared to be adaptable for measurement of isotopic enrichment in other biological samples Tetraphenylporphyrin reacts quickly and quantitatively to form chelates with nearly all of the transition metals (M The mass spectrum of a TPP chelate is dominated by the molecular ion cluster (Figure 1) the molecular ion is also the base peak so it is well-suited for quantitation of isotope ratios ... 

In summary, ionisation potentials, dissociation and cohesive energies for mercury clusters have been determined. The mass spectrum of negatively charged Hg clusters is reported. The influence of the transition from van der Waals (n < 13), to covalent (30 < n < 70) to metallic bonding (n > 100) is discussed. A cluster is defined to be metallic , if the ionisation potential behaves like that calculated for a metal sphere. The difference between the measured ionisation potential and that expected for a metallic cluster vanishes rather suddenly around n 100 Hg atoms per cluster. Two possible interpretations are discussed, a rapid decrease of the nearest-neighbour distance and/or the analogue of a Mott transition in a finite system. Electronic correlation effects are strong they make the experimentally observed transitions van der Waals/covalent and covalent/metallic more pronounced than calculated in an independent electron theory. 

MALDI spectrum of a hydroxyl functional polymer prepared by GTP the level of the impurity is easily seen and the success of this reaction clearly observed. However, this is not a universally applicable technique. Perhaps the most topical living polymerisation at present is transition metal mediated radical polymerization. This typically gives a polymer with a tertiary halide terminal group. This group, as has nitroxide, has been found to be very labile in the mass spectrometer leading to fragmentation. 

At the same time cis Smalley and students at Rice University, Houston Texas, developed the laser vaporization method for production of clusters [84], a similar set-up was built at Exxon s Research Laboratory, New Jersey, USA, by the group of Kaldor and Cox [102,103]. They studied in particular transition metal clusters but also produced clusters of carbon containing up to more than hundreds of atoms as shown in the mass spectrum in Fig. 12. 

The addition of chelating agents such as /ranx-l,2-diaminocyclohexane-lV,yV,yV, yV -tetraacetic acid (CDTA) and/or triethylamine (TEA), removes the bound transition-metal cations and Mg + ions from RNAs and enhances mass measurement accuracy [9]. Figure 13.5, the ESI spectrum of E. coli 5S rRNA (120 nt), demonstrates the utility of this approach. Before acquiring the ESI mass spectrum, the sample of rRNA was precipitated from 2.5 M ammonium acetate solution, and 500 pmol of CDTA and 10 tiL of 0.1% TEA solution were added. Two major rRNA components were detected. In the absence of CDTA and TEA, no useful data could be obtained. 

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