Adduct ions, formation

The analyte may be neutral or ionic. Solutions containing metal salts, e.g., from buffers or excess of noncomplexed metals, may cause a confusingly large number of signals due to multiple proton/metal exchange and adduct ion formation. [91] The mass range up to 3000 u is easily covered by FAB, samples reaching up to about twice that mass still may work if sufficient solubility and some ease of ionization are combined. 

Due to the Si — N interaction in silatranes, the protonated molecular ions MH+ are usually less abundant than the molecular ions M+. Further decomposition of both types of ions involves a loss of the substituent X and a subsequent adduct ion formation. 

Several other sample preparation methods were developed to simplify the solution-deposition procedures. For example, Cooks and coworkers studied adduct ion formation (cationization) of several organic compounds when the organic was burnished (rubbed) onto a metal foil, mixed with a metal salt and then burnished onto a metal foil, or just mixed with metal powders or salts and pressed into pellets. Not only did the SIMS spectra show dramatic differences is the efficiency of adduct ion formation for different metals, but the sample preparation methods had an equally dramatic effect on the SIMS spectra [18]. 

Pseudomolecular Ions. In contrast to the traditional MS, the highest mass peaks in ESI/APCI spectra are not always the molecular ion of interest. Instead, pseudomolecular ions, or noncovalent complex ions, are commonly observed. The pseudomolecular ions are generally formed by the analyte-adduct interaction in the solution system that is preserved as a result of the soft ionization of the ESI/APCI process. These ions are also formed by analyte-adduct gas-phase collisions in the spray chamber [49]. The exact mechanisms of how the analyte adducts are formed in ESI/APCI still remain unresolved at this point. More often than not, the adduct ion formation is a major cause for the low detection limit for ESEAPCI MS. However, these associative processes have also created interest in the study of drug-protein/ drug-oligonucleotide gas-phase complexes that benefit from the ability of ESI/APCI MS analysis. 

Atrazine and two major degradation products, desethylatrazine and desisopropylatrazine have been analysed by using acetonitrile-water (50 50) and 0.05 M ammonium acetate. As regards to the chloroatrazines, it should be commented that in PI mode TSP LC-MS a common feature in the adduct ion formation has been observed, with the formation of [M + H + CHjCN] as base peak with the exception... 

The examples discussed above refer to adduct ion formation, where covalent bonds are formed in the Cl plasma. However, with the increasing importance of alternative ionization techniques, such as thermospray (TSI) and, in particular, electrospray ionization (ESI), a wealth of non-covalent ion/molecule adduct ions can be generated and studied nowadays. One recent example concerns the formation of ion/solvent adducts, [M- -So]+, with M including 3-aminophenol, 3-(methylamino)phenol and 3-(dimethylamino)phenol, and several hydroxypyrimidines, among other aromatic molecules. The relative abundances of ions [M- -H]+, [M -h So -h H]+ and [M - - 2 So - - H]+ were studied as a function of the temperature and the pH, with the solvents being mixtures of methanol/water and acetonitrile/water which may contain ammonium acetate as an additive . Quite in contrast to this empirical study on proton-bound ion/molecule complexes, the non-covalent, open-shell adduct ions [l + -h NH3] were investigated with respect to their intrinsic reactivity. These adduct ions were generated from phenol and ammonia by laser ionization of a... 

Correction of LC-MS RRFs for relative ion abundance. Equal sensitivities for parent and analogue should initially only be assumed for the total ionization. SIR or MRM techniques will be used for trace analysis of toxins. For SIR, the full-scan spectra of parent and analogue should be checked. The assumed RRF of 1.0 should be adjusted if the ions monitored differ in their relative abundances (as % of TIC) due to differences in in-source fragmentation and adduct ion formation. It is probable that the relative intensities in the MS/MS daughter ion spectra will vary between parent and analogue. A cross-calibration... 

Adduct ion formation is a common feature of most ESI or APCI—MS analysis. Although these ions can complicate the mass spectra, once understood, they are useful for the confirmation of the molecular weight of an analyte of interest. 

Papers describing flow or loop injection with atmospheric pressure ionization and (tandem) mass spectroscopy. In a short communication on ES-MS of the A -palmitoylgalactosylceramide li et al. (1993) focus on adduct ion formation with use of methanol/chloroform in negative ion mode. 

Poon C, Kaplan H, Mayer PM. Methylating peptides to prevent adduct ion formation also directs cleavage in collision-induced dissociation mass spectrometry. Eur J Mass Spectrom. 

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