Mass spectrometry analysing molecular ions

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

The study of the interactions between organic compounds and aUtali-metal cations, in the gas phase, is related to many topics such as ion solvation, catalysis and molecular recognition. Furthermore, mass spectrometry has been used for the analyses of organolithium compounds and supramolecular assemblies that contain lithium cations. Alkali cationization is an important ionization technique, implemented for the analyses of a wide range of organic compounds. Finally, gas-phase studies are also useful for the quantitative determination of lithium cation affinity. The interaction between lithium cation and organic substances is thus related to different aspects of gas-phase chemistry and mass spectrometry. 

The mass spectrometry does not involve an interaction between electromagnetic radiation and sample molecule. The functions of a mass spectrometer are to produce positive ions from the sample under investigation, to resolve these ions into a series of ion beams that are homogeneous with respect to their mass/charge ratio (m/e), and to measure the relative abundance of the ions in these beams. The main applications include the molecular weight and structural determinations (Bieman, 1992). Mass spectrometry has emerged as the method for rapid analyses of protein sequences and annotation of their databases (Mann and Pandey, 2001). 

Mass spectrometry is typically a flow experiment in that molecular ions are being continuously formed and are continuously reacting and it is ion currents or count rates which are measured. The molecular ions may be formed according to some sequence of pulses, but the essential situation remains the same. Generally, the molecular ions are formed at some more or less well-defined position in space and the lifetimes, t, of ions correlate with transport of the ions away from their position of formation through the analysers and towards the detector. 

Regarding the mass range, DNA ions of 108 Da were weighed by mass spectrometry [77], In the same way, non-covalent complexes with molecular weights up to 2.2 MDa were measured by mass spectrometry [78], Intact viral particles of tobacco mosaic virus with a theoretical molecular weight of 40.5 MDa were analysed with an electrospray ionization charge detection time-of-flight mass spectrometer [6]. 

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