Electrospray attribute

The raw electrospray spectrum obtained is shown in Figure 5.14. Maximum entropy processing of these data yielded the spectrum shown in Figure 5.15, which shows the presence of two species with molecular masses of 14293.6 and 14 309.6 Da, with the latter being attributed to partial oxidation of the parent protein. 

It is well known that electrospray ionization (El) suffers from suppression effects when polar/ionic compounds other than the analyte(s) of interest, such as those originating from the sample matrix, are present, with this phenomenon being attributed to competitive ionization of all of the appropriate species present [33]. Matrix effects can, therefore, be considerable and these have two distinct implications for quantitative procedures, as follows ... 

Mass spectrometry is a useful tool to detect the existence of reactive iron-imido intermediates. In intramolecular aromatic aminations, Que and coworkers used electrospray ionization mass spectrometry to show the presence of a molecular ion at m/z 590.3 and 621.2, which could be attributed to the formation of [(6-(o-TsN-C6H4)-TPA)Fe ]+ and [(6-(o-TsN-C6H4)-TPA)Fe° OMe)]+. With the isoto-... 

When experiments with electrospray producing H3N(CH2)pNH2+ ions were performed in this laboratory,56 it was found that doubly protonated ions could be obtained from methanol-water solutions only when p > 4. For p < 4 only the singly protonated ions were observed, even though the doubly protonated ions are known to be present in the solution. We attribute the failure to observe the doubly protonated ions with p < 4 to the occurrence of charge reduction by deprotonation. Probably methanol, whose gas-phase basicity is greater than that of water, is involved in the deprotonation. The diprotonated diammines, p > 4, could all be dehydrated down to the naked ion either in CID experiments or at higher temperature. 

Figure 2.22 Charge attribution (a) and deconvolution (b) of the electrospray positive ion mass spectrum of cytochrome c (see Figure 2.21)...

Met-0-Me /(R,R,R,R)-1 in the FAB spectra reduces to ca. 1.5 1, if ESI is used to generate the ionic complexes. This observation appears to be general for all host-guest pairs studied and it was attributed to the electrospray process, although no real... 

Utilization of capillary columns in conjunction with micro ESI devices is becoming a new trend in the field of LC/MS. Capillary HPLC has become a particularly important technique in situations where the supply of analyte is limited, such as in proteomic analysis. According to studies conducted by Smith et al., only one in a hundred thousand of analyte molecules present in solution eventually reach mass detection in a conventional ESI interface. Smith et al. attributed this poor electrospray... 

Mass spectrometry is a valuble tool with which an abundancy of structural information may be obtained from a minute amount of material. Capillary electrophoresis may be interfaced with mass spectrometry by electrospray ionization [124-126] or continuous-flow, fast-atom bombardment methods [127,128]. Several reviews discuss applications of the interfacing techniques, and address the attributes and disadvantages associated with these methods [129,130]. Critical parameters involved in the optimization of CE-electrospray ionization mass spectrometry analysis have been reviewed as well [131],... 

Mass spectrometry (MS) has become one of the most important analytical tools employed in the analysis of pharmaceuticals. This can most likely be attributed to the availability of new instrumentation and ionization techniques that can be used to help solve difficult bioanalytical problems associated with this field (1-8). Perhaps the best illustration of this occurrence is the development of electrospray (ESI) and related atmospheric-pressure ionization (API) techniques, ion-spray (nebulizer-assisted API), turbo ionspray (thermally assisted API), and atmospheric pressure chemical ionization (APCI nebulization coupled with corona discharge), for use in drug disposition studies. The terms ESI and ionspray tend to be used interchangeably in the literature. For the purpose of this review, the term API will be used to describe both ESI and ionspray. In recent years there has been an unprecedented explosion in the use of instrumentation dedicated to API/MS (4,6,8-14). API-based ionization techniques have now become the method of choice for the analysis of pharmaceuticals and their metabolites. This has made thermospray (TSP), the predominant LC/MS technique during the 1980s, obsolete (15). Numerous reports describing the utility of API/MS for pharmaceutical analysis have appeared in the literature over the last decade (7). The... 

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