Small Neutral Losses

The LD spectrum of the tridecapeptlde neurotensin (Figure 4), shows several differences. Here fragmentation results almost exclusively from small neutral losses. A protonated molecular ion is still one of the major ions observed (m/z = 1673) and some cationized (K+) fragment species are apparent as well as a small amount of cationized molecular ion (<5%). Resolution has begun to be degraded to some extent, partially due to the decrease in overall ion signal which necessitates transformation of fewer data points to maximize signal to noise ratio. 

Mixtures of several different matrices have been reported for an improved performance, for example, 1 1 (w/w) mixtures between HCCA and DHB resulted in a lowered chemical noise and slightly improved sequence coverages [148]. However, so far only DHBs (a mixture of 90-95% 2,5-DHB and 5-10% 2-hydroxy-5-methoxybenzoic acid) has found relatively widespread appHcation for proteins [149]. The additive soflens the desorption and Hmits the small neutral loss, thereby improving mass resolution. A mixture of different trihy-droxyacetophenones is sometimes used for the analysis of nucleic acids [150]. 

In Unknown 5.13, chemical ionization and exact mass measurements show that mjz 119 is formed by the loss of C2H5 from the molecular ion such small neutral losses are indicative of the structure. Did you identify both important ion series ... 

The heaviest ions due to the losses of small neutral particles from the M+, that is without notable transformations of the initial molecule. 

Proximity effects and ortho interactions in 2,2/-disubstituted diaryl amines have been reported104. Thus, phenazine, phenazine-N-oxide and carbazole were formed by loss of small neutral fragments, such as NO, NO2 and NO3, from the molecular ions, as illustrated by the formation of carbazole from 2,2/-dinitrodiphenylamine see Scheme 34. Of particular interest is the loss of NO3, as demonstrated by high-resolution MS data and metastable ion spectra104. 

The negative ion electrospray MS of fatty acid hydroperoxides exhibits various typical features that may be useful for characterization of this type of compounds, such as loss of small neutral molecules and fragmentation associated with the position of the OOH group. The [M — H] and [M — H2O peaks are usually most abundant and cleavage of the double bond allylic to the hydroperoxy group is also observed. The features of the fragmentation after loss of H2O in the MS of a fatty acid hydroperoxide are the same as those observed in the MS of the analogous keto acid . ... 

Using accurate-mass determination with a Q-TOF instrument, March and Miao [16] studied the fragmentation of deprotonated kaempferol. The fragments observed were apparently not consistent with the above discussion. Accurate-mass assisted interpretation indicated that most fragments can be explained from consecutive losses of small neutrals, especially HjO, OH , CO, CHjO, and CjHjO. 

Typical fragmentation of both types of base involves the loss of small neutral molecules such as HCN, CO, and CH3CN, as well as some extensive rearrangements in aromatic compounds. The most common derivatization, silylation under normal conditions (TMSC, HMDS/TMSC, BSA, or BSTFA/TMSC, V, 20 min - 2 hr), with or without pyridine as a solvent and base catalyst, usually leads to the enolic forms of the bases via the corresponding silyl ether. The persilylated derivatives are volatile enough to be used in gas chromatography-mass spectrometry (GC-MS). This enhancement of volatility compared to that of the free bases is the key factor making GC-MS a widely used analytical method in this area. 

Mass spectra of a series of 20-pyridyl steroids were measured, and the fragmentations discussed. Intramolecular hydrogen transfer in mass spectra rearrangements involving the loss of small neutral molecules has been reviewed.The loss of water and ammonia from hydroxy-amino- and amino-steroids was quoted. 

The table also summarizes a set of information that may be useful when interpreting product ion spectra, mass differences produced by the loss of a small neutral molecule. These losses are observed for both the b- and y-ion series if that ion contains a particular amino acid. As a result, observation of these losses can be used as a general indicator of amino acid content of the peptide or product ion. The most common loses are water (18Da) and ammonia (17Da). Loss of water typically occurs from the alcohol-(serine and threonine) or carboxylic acid- (asparatate and glutamate) containing anfino... 

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