[M + 11]+˙ and [M + 11]−˙ ions in the nitrogen positive and negative ion chemical ionization mass spectra of aromatic amines

✍ Scribed by Elizabeth A. Stemmler

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 677 KB
• Volume: 28
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210280904

✦ Synopsis

The N, negative ion chemical ionization (NICI) mass spectra of aniline, aminonaphthalenes, aminobiphenyls and aminoanthracenes show an unexpected addition appearing at [ M + 11 1 -'. This addition is also observed in the N, positive chemical ionization (PCI) mass spectra. An ion at IM -151-is found in the N K I spectra of aminoaromatics such as aniline, 1-and 2-aminonaphthalene and 1-and 2-aminoanthracene. Ion formation was studied using labeled reagents, variation of ion source pressure and temperature and examination of ion chromatograms. These experiments indicate that the [ M + 11 1 -*, [ M -151 -' and [ M + 11 1 +' ions result from the ionization of analytes altered by surface-assisted reactions. Experiments with "N, , [ "N 1 aniline, [ 2,3,4,5,6-2H,1aniline and [ '3C,[aniline show that the [M + 111-' ion corresponds to [ M + N -3H]-*. The added nitrogen originates

from the N, buffer gas and the addition occurs with loss of one ring and two amino group hydrogens. Fragmentation patterns in the N, PCI mass spectrum of aniline suggest that the neutral product of the surface-assisted reaction is 1,4-dicyanobuta-1,3-diene. Experiments with diamino-substituted aromatics show analogous reactions resulting in the formation of [ M -4H I -* ions for aromatics with ortho-amino groups. Experiments with methylsubstituted aminoaromatics indicate that unsubstituted sites ortho to the amino group facilitate nitrogen addition, and that methyl groups provide additional sites for nitrogen addition.

'H) (MSD Isotopes), and ['3C,]aniline (99% I3C) (MSD Isotopes) and other standards ranged in concentration from 10 to 100 ng p1-l. Benzene, methylene chloride and hexane (Burdick and Jackson Laboratories, Muskegon, MI, USA) were used as solvents.