| Mass spectrometry has become one of the indispensable tool in analyticaldisciplines, because of its powerful ability to identify. During analysingthe mass resolution, how to extract the correct data from the vast amountsof data, and interprete the mass spectrometry, then determine therelationship between the structure of the compound and the cracking law isstill urgent problem today. This paper adopts a new method, to explain thecracking mechanism between molecules and ions, ions and ions in the massspectrum, by the stable configurations to be determined, so as to obtain thefragmentation pattern of the compound, and then summarize the cracking ofsimilar material.In the negative ion and manually extracted ion mode, to obtain the totalions mass chromatogram and multi-level mass of five kinds of anthraquinonederivatives (rhein, chrysophanol, physcion, emodin, aloe-emodin) inelectrospray ionization ion trap mass spectrometry (ESI-ITMSn).By analyzingthe compounds induced dissociation mass spectrometry(CIDMS), preliminarilydetermine the structure of each ion fragmentation. Quantum chemistrysemi-empirical AM1method were used to obtain the initial geometry of themolecular and fragment ions of the anthraquinone compounds, and then basedon the density functional theory (DFT), at the level of B3LYP/6-31G (d), thegeometry structure of fragment ions of the anthraquinone compounds wereoptimited, and the frequency were calculated, by analysing thecharacteristic of the fragment ions including geometry parameter, thechanges of charges and spin density and frontier molecular orbital, includethe corresponding bond dissociation energy were analyzed by virtue of DFTat ROB3LYP/6-31G (+)(2d,2p) level, stable structures of the fragment ionsfrom molecular were predicted and fragmentation site were determined，toobtain the fragmentation pathway. The results showed that: five kinds of anthraquinone compounds were easyto dissociate in the electrospray ionization ion trap mass spectrometry. Inthe cracking process, mainly occurred dehydrogenation and took off carbonmonoxide and carbon dioxide.(1) dehydrogenation. The five kinds ofanthraquinone compounds had three rings,which were connected to phenolic hydroxyl groups in the ring A and ring C,but a carboxyl group attached to the ring C of rhein. The phenolic hydroxylgroups and carboxyl group had a high activity in the ionization process. Itwas calculated that the results of energy, the positions of losing thehydrogen were took place at the ring C, which was named14and the bind changedfrom C-O to C=O, but the carboxyl group of rhein lost an hydrogen at12，and the whole ion was negative, and the charges of ring C changed irregularly.After geometry optimization, the molecular ions were in the same plane, andeach substituent group was in a free extended state.(2) Losing carbonmonoxide. The small molecules CO were lost from five compounds in the crackingprocess, evenly occurred consecutively. The findings after analysing, thesite of losing carbon monoxide firstly was10in the ring B. Because thecleavage energy was smallest, the changes of bond length and charge werelargest, the spin density of carbon and oxygen and the proportion of takingpart in the frontier molecular orbital were more. The second carbon monoxidewas lost at the position of14in the ring C after decarboxylation andconstrictor ring, the next at the site of6in the ring A, at last occurredat7in the ring A.(3) Losing carbon dioxide. By analyszing the data of massspectrometry experiments, lost a group, whose quality was44, we consideredit as carbon dioxide. It was easy to lose carbon dioxide from fragment ionsafter studying the structure of them, which had a consecutive hydroxyl.However, without this, the form of carbon dioxide caused deoxygenation atthe14,then losing carbon monoxide at the position of6. In conclusion, by using quantum chemical method, not only effectivelyexplain the cracking behavior of anthraquinones in mass spectrometry, butalso laid the foundation for the studying of cracking mechanism of othercompounds. |
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