Transition metal ions ionization methods

The combination of laser ionization and Fourier transform mass spectrometry (FTMS) has proved to be ideally suited for the study of gas-phase ion-molecule reactions involving metal ions (1-7). The laser source permits the generation of virtually any metal ion in the periodic table from a suitable metal target (8). The FTMS (9-14) stores these ions in an "electro-magnetic bottle" for times t)rpically on the order of msec to sec (hours are possible) permitting the study of their chemistry and photochemistry. These studies are further facilitated by the unusual ion and neutral manipulation capabilities of the FTMS which permit complex multistep processes to be monitored in an MS fashion (1-4). These capabilities have made laser ionization-FTMS a prominent method in what has been a rapidly growing arsenal of techniques for studying gas-phase transition-metal ion species. 

On the other hand, it has proved possible to activate a C-C bond by using bare ( naked ) transition metal ions, generated by various ionization methods in the gas phase [165]. Using an ion-beam instrument, for example, Armentrout and Beauchamp [166] were able to show that the reaction of Co+ with -butane gives C0C2H4. An exothermic and quite facile C-C insertion by the metal is thought... 

Adducts with metal ions are important for the successful MALDI analyses of nonpolar compounds. Similarly to the ESI method, their formation very often takes place as a result of the presence of traces of metal salts. Addition of small amounts of Na+ and K+ ions is used for helping the ionization of analytes whose proton affinities are low. Transition-metal ions have been successfully applied when no other ionizing reagents work. For example, Ag+ ions are extremely effective in the MALDI analysis of polymers having no heteroatoms. 

Applications of electrospray mass spectrometry (ESMS) to the study of reactions mediated by transition-metal complexes are reviewed. ESMS has become increasingly popular as an analytical tool in inorganic and organometallic chemistry, in particular with regard to the identification of short-lived intermediates of catalytic cycles. Going one step further, the coupling of electrospray ionization to ion-molecule techniques in the gas phase yields detailed information about single reaction steps of catalytic cycles. This method allows the study of transient intermediates that have previously not been within reach of condensed-phase techniques on both a qualitative and quantitative level. 

The ICP has proliferated as a method of converting chemical compounds into their elemental constituents which subsequently emit light of characteristic wavelengths. Accordingly, ICP has been used extensively as an emission source for optical detection systems in order to perform elemental analysis. Since each element can emit hundreds of optical lines, the use of ICP/AES for multiple element analysis, or for the detection of elements in unknown or concentrated matrices, can suffer from interferences due to spectral overlap. By contrast, ICP-MS provides inherently simpler spectral Information. An example of such a spectrum is demonstrated in Figure 2 showing a typical ICP-MS scan for a 10 ug ml"l solution of mixed transition metals. The demonstrated sensitivity here is 10 to 10 counts s l per ug m1"l and, coupled with the nearly universal ionization efficiency of the ICP ion source, provides typical detection limits in a narrow range between 0.1 to 10 ng.ml" for most elements. In fact over 90% of the elements in the periodic table are accessible for such analytical determinations. 

The oxidation potential represents the ability of a metal atom (M) to be ionized to an ion (M" ") with loss of an electron. For the oxidation of organic molecules, transition metal compounds containing chromium, manganese, ruthenium, selenium, silver, or cerium are often used. The oxidation potential is therefore a useful method for examining the oxidizing power of these reagents. 

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