Triethylamine, mass spectrum

Acids and bases are used to increase ionisation by protonation or deprotonation of the analyte, and it is important to choose the buffer and buffer strength very carefully because both have a noticeable effect on sensitivity. In the positive mode, high PA additives such as triethylamine (TEA) will successfully compete with the analyte for available protons and show an intense ion at miz 102. Sensitivity can drop substantially when TEA is buffered with trifluroacetic acid (TFA). This is shown in Figure 6.3. The top diagram shows the mass spectrum of a compound analysed using acetonitrile/H20/TFA as the eluent and shows MH at mIz 511. The mass spectram of the same compound when analysed using... 

The addition of chelating agents such as /ranx-l,2-diaminocyclohexane-lV,yV,yV, yV -tetraacetic acid (CDTA) and/or triethylamine (TEA), removes the bound transition-metal cations and Mg + ions from RNAs and enhances mass measurement accuracy [9]. Figure 13.5, the ESI spectrum of E. coli 5S rRNA (120 nt), demonstrates the utility of this approach. Before acquiring the ESI mass spectrum, the sample of rRNA was precipitated from 2.5 M ammonium acetate solution, and 500 pmol of CDTA and 10 tiL of 0.1% TEA solution were added. Two major rRNA components were detected. In the absence of CDTA and TEA, no useful data could be obtained. 

The mass spectral fragmentation patterns of amines also aid in structural assignments. For example, the mass spectrum of V,V-diethylethanamine (triethylamine) shows the peak for the molecular ion at m/z = 101 (Figure 21-5). However, the more prominent base peak is at m/z = 86 and is caused by the loss of a methyl group by a-cleavage (Section 11-10). Such fragmentation is favored because it results in a resonance-stabilized iminium ion. 

Fig. 7.7 MALDI-TOF mass spectrum of a fraction of polycarbonate prepared by triethylamine-catalyzed hydrolytic poly condensation of bisphenol-A bischloroformiate (Cl000 means cycle with DP = 100). Reproduced from Ref. [44, Fig. 6] with permission (Copyright Wiley-VCH Verlag GmbH Co KGaA)...

C-H groups. A sharp band at 1440 is characteristic of the Sb-Ph stretch. Bands assigned to the formation of the ether linkage are found. Bands characteristic of the symmetric C-0 stretch are present at 1063 and 997. A band characteristic to the formation of the Sb-O linkage is assigned as appearing at 765. Bands at 738 and 690 are characteristic of C-H out-of-plane deformation for monosubstituted benzene. Products derived from the use of triethylamine alone as the added base had a spectrum where the bands associated with the triphenylantimony moiety were diminished. Even so, mass spectra of these products exhibit ion fragments expected from the presence of the triphenylantimony moiety. 

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