Amines fragmentation mass

Amines have odd numbered molecular weights which helps identify them by mass spectrometry Fragmentation tends to be controlled by the formation of a nitrogen stabilized cation... 

An example of how information from fragmentation patterns can be used to solve structural problems is given in Worked Example 12.1. This example is a simple one, but the principles used are broadly applicable for organic structure determination by mass spectrometry. We ll see in the next section and in later chapters that specific functional groups, such as alcohols, ketones, aldehydes, and amines, show specific kinds of mass spectral fragmentations that can be interpreted to provide structural information. 

Summary If the molecular weight is odd, then the compound contains an odd number of nitrogens. Fragment ions observed at even-mass numbers suggests the presence of nitrogen. The loss of ammonia is fairly common in nitrogen compounds and may not indicate exclusively that an amine is present. Chemical derivatization will easily determine if the unknown is a tertiary amine. 

ItAmines show a powerful tendency to fragment beta to the nitrogen atom. This mass is not Characteristic only of primary compounds, because the ion is formed from other amines fby rearrangement. 

The mle of the largest alkyl loss may be quantifiable. Zahorszky [4], studying fragmentation of alcohols and amines, showed that the peak intensities of [M — Alk,]+ ions may be calculated, as the ratio of intensities of these peaks is inversely proportional to the ratio of the masses of the corresponding ions. The intensities of the peaks of secondary ions should be added to the intensity of the corresponding primary ion peak. This mle is not applicable to the loss of methyl radical. 

Fig. 2.12.15. FIA-APCI-MS-MS(+) (CID) product ion mass spectrum of cationic surfactant compound (m/z 538) fatty acid polyglycol amine type observed in the Saale river, Germany (general formula R—N H((CH2—CH2—OH)x)—(CH2—CH2—OH)y X fragmentation behaviour of [M]+ parent ion at m/z 538 under CID conditions is presented...

Attention should be paid to the appearance of spurious peaks in the fragmentation patterns of amines determined by GC-MS, when the analytes came into contact with methanol or ethanol as solvents. Thus, for example, Schiff bases may be formed on condensation of a primary amine with traces of formaldehyde or acetaldehyde present in the solvent. Although the peaks of such product may be unresolved in the chromatogram, they may appear as ions with mass increments of +12 or +26 in the mass spectrogram, complicating the identification of the analyte, as was the case with some amphetamine drugs99. 

Duffield, A.M. Budzikiewicz, H. Williams, D.H. Djerassi, C. Mass Spectrometry in Structural and Stereochemical Problems. LXIV. A Study of the Fragmentation Processes of Some Cyclic Amines. J. Am. Chem. Soc. 1965, 87, 810-816. 

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