Combined Ion/Molecule Reactions and Multi-stage Tandem Mass Spectrometric Techniques in an Ion Trap Mass Spectrometer for the Characterization of Conjugated Ethylenic Epoxides. 1—Protonating Agents
✍ Scribed by Mayran Sharifi; Jacques Einhorn
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 253 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0951-4198
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✦ Synopsis
The potential of the ion trap mass spectrometer to characterize isomeric long-chain conjugated mono-or diethylenic epoxides was investigated using the multi-stage tandem mass spectrometric (MS n ) facilities of the instrument. In the proposed approach, mass-selected reagent ions obtained from common protonating agents were prepared and allowed to react with the neutral epoxides for controlled reaction times. Positive-ion chemical ionization using the t-C 4 H 9 + ion (t-C 4 H 9 + /CI) and CH 5 + or C 2 H 5 + /CI were found to provide the most informative spectra (e.g. diagnostic ions generated by the decomposition of the MH + ion through competing pathways) as compared with NH 4 + /CI. An acylium diagnostic ion (A + ) stemming from the epoxide side was produced in both types of epoxides but its relative abundance was optimal using CH 5 + or C 2 H 5 + which are of low proton affinity. In the case of the dienes, an [M + A] + covalent adduction, probably resulting from a [4 + 2 + ] Diels-Alder cycloaddition process and thus specifically assigning such a system was generated (C 2 H 5 + /CI conditions). The MS n capabilities of the instrument were also used for the determination of the origin and structure of the diagnostic ions or for additional selectivity.