Tandem fragmentation patterns

Substituted tetrazoles reacting in the mass spectrometer with acyl ions afforded 2,5-disubstituted 1,3,4-oxadiazoles with nitrogen loss. Tandem mass spectrometry allowed for the collision-induced dissociation of the products. Chemical ionization was the better method to make the transformation. A scheme for the transformation of 5-substituted tetrazoles into 2,5-disubstituted 1,3,4-oxadiazoles was proposed (Scheme 1) <2001JMP1069>. The fragmentation patterns of monocyclic l,3,4-oxadiazolium-2-thiolates have been proposed by Ollis and Ramsden <1974J(P1)645>. 

The straightforward approach to de novo sequencing sometimes fails, for example, due to the low quality tandem mass spectra. Often it is not caused by the equipment settings or operator s capabilities, but just by unfavorable fragmentation pattern of a given peptide. Among possible approaches to solve such issues is chemical derivatization of peptides. 

An ultrapure polymer is made of chains of the type G1-AAAAAAA-G2, where A is the repeat unit and G1 and G2 are end-groups. One considers the mass number of one of the MS peaks, subtracts the mass of the cation (e.g., H, Li, Na, Ag), and then repeatedly subtracts the mass of the repeat unit, until one obtains the sum of the masses of G1 + G2. For this purpose, a linear best fit can also be used. Tandem mass spectrometry is particularly useful since, from the analysis of ion fragmentation patterns, one can deduce the mass of G1 and, separately, the mass of G2. 

However, mass spectrometry itself offers two additional degrees of freedom . One can either resolve the complexity of a sample by going to high or even ultra-high mass resolution or one can employ tandem MS techniques to separate the fragmentation pattern of a single component from that of others in a mixture. [2,3] In practice, the coupling of separation techniques to mass spectrometry is often combined with advanced MS techniques to achieve the desired level of accuracy and reliability of analytical information. [1,7,24-27]... 

The location of the double bonds in unsaturated glycerophosphocholine (GPC) lipids is made difficult mainly due to the limited amounts of these compounds isolated from cells. When a thin layer of a GPC lipid is exposed to the action of ozone, partial or total ozonization of the unsaturated fatty acid residues may take place, depending on the particular compound being analyzed. The ozonized hpid is dissolved and analyzed by tandem MS. A typical injection into the instrument may be 5 xL containing 10-20 ng of the lipid. An illustrative example is the ozonized l-stearoyl-2-arachidonoyl-GPC, showing the systematic fragmentation pattern in Scheme 21, typical of the ozonized GPC lipids. Thus, the molecular peak appears increased by one nominal unit (M + H, m/e 1002),... 

The fragmentation patterns and characteristic fragment ions for the carotenoids observed in FAB-MS and LSIMS tandem mass spectra are also observed in the tandem mass spectra obtained following ESI (see Basic Protocol 4), APCI (see Basic Protocol 5), and other methods. A detailed account of structure determination of carotenoids using FAB ionization with CID and MS/MS is presented in van Bree-men el al. (1995). Finally, another advantage of MS/MS is that matrix ions formed during FAB-MS or LSIMS, and any other contaminating ions, are eliminated, which simplifies interpretation of the mass spectrum. 

Contains the most complete set of tandem mass spectra of carotenoids and their interpretation. Fragmentation patterns and characteristicfragment ions described here are common to all CID tandem mass spectra of carotenoids. 

Wang J, Aubry A et al (2010) Effect of mobile phase pH, aqueous-organic ratio, and buffer concentration on electrospray ionization tandem mass spectrometric fragmentation patterns implications in liquid chromatography/tandem mass spectrometric bioanalysis. Rapid Commun Mass Spectrom 24 3221-3229... 

In 2012 an ESl-MS investigation of Rh-catalyzed [2 + 2 + 2] cycloaddition reaction was reported [53]. In this DFT-supported study, several key intermediates were observed and characterized by MS/MS tandem spectrometry. Although reactant and product are neutral, the charged catalyst provided a good opportunity to intercept visible intermediates. A species with m/z 974.1 was assigned based on its accurate mass and fragmentation pattern however, as is often the case with mass spectrometry-based experiments, the authors were unable to distinguish between isomeric structures (Scheme 6). 

Tandem MS (MS/MS) has proven a particularly powerful tool, comparing fragmentation patterns of MS/MS spectra with established databases, enabling protein identification. 

Tandem mass spectrometry (MS-MS) using quadrupole mass analyzers or ion-trap analyzers facilitate the conducting MS-MS experiments and increases the sensitivity of detection. Fragmentation patterns of anthocyanins generally show the loss of a glycoside or... 

The positive electrospray ionization tandem mass spectrometry (ESTMS/ MS) of lornoxicam was obtained using an Agilent 6410 QQQ mass spectrometer with collision energy 10 eV using argon as collision gas and is shown in Fig. 6.14. Table 6.8 shows the mass fragmentation pattern of the drugs. 

Tandem fragmentation-cyclization of bicyclic ketones connected to unsaturated side chains have been used to construct hi-, tri-, and spirocyclic ketones [334], Cossy et al. have shown that depending upon the substitution pattern, ketyl radical anions obtained from photochemically induced electron transfer from amines to cyclopropylketones lead either to the formation of 3-substituted cycloalkanones or to ring expanded products (Scheme 78) [335],... 

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