Small-molecule , generally mass spectrometry

Photoionization ti me-of-fli ght mass spectrometry is almost exclusively the method used in chemical reaction studies. The mass spectrometers, detectors and electronics are almost identical. A major distinction is the choice of ionizing frequency and intensity. For many stable molecules multi photon ionization allowed for almost unit detection efficiency with controllable fragmentation(20). For cluster systems this has been more difficult because high laser intensities generally cause extensive dissociation of neutrals and ions(21). This has forced the use of single photon ionization. This works very well for low i oni zati on potential metals ( < 7.87 eV) if the intensity is kept fairly low. In fact for most systems the ionizing laser must be attenuated. A few very small... 

The general method for ASMS is shown in Fig. 4.1. In ASMS, the target concentration is generally set at 5-10 xM, so that at equilibrium, ligands with affinities of no weaker than Ku 10 xM will be significantly bound and, therefore, retained in the ultrafiltration steps. The minimal concentration of each small molecule is dictated by the eventual need to detect ligands by mass spectrometry after several cycles of ultrafiltration and subsequent extraction. In order to ensure detection just above baseline for the vast majority of compounds, which vary in inherent ionization properties and efficiency of mass spectrometric visibility, the starting compound concentration is set at 1.5 pM per compound. The mixture... 

Now that you have a basic understanding of the information that is available in an IR absorption spectmm, it is possible, with some additional information, to work out the likely structure of an unknown for small molecules (MW < 300). For unknowns where the molecular weight has been determined by mass spectrometry the analyst generally takes the following approach. 

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