El Mass Spectra of Organic Salts

Ammonium, phosphonium, oxonium salts and the like cannot be evaporated without substantial or complete decomposition, and thus EI-MS does not serve well for their characterization. Nevertheless, if a sample that happens to be an organic salt has incidentally been analyzed by El-MS, it is helpful to know about their recognition. The El mass spectra usually appear to result from the corresponding amines, phosphines, or ethers, but fortunately, the anion cannot hide . 

Example The El mass spectrum of tetrabutylammonium iodide shows a peak of low intensity (0.6%) for the [Bu4N] ion, m/z 242. A molecular ion of the salt that would occur at m/z 369 is not observed. The majority of the sample decomposes and the spectmm closely resembles that of pure tributylamine showing its molecular ion peak at m/z 185 (the fragmentation of which is explained in Chap. 6.11.1). Closer inspection, however, reveals the existence of peaks at m/z 127 and 128 corresponding to T and Hl , respectively (Fig. 6.40). 

---