Charge Inversion Mass Spectrometry Research Articles

Fragmentation behaviour ofN-acylamino-O-alkyl ester derivatives of an aliphatic tripeptide in negative ion mass spectrometry

The N-acetyl-, N-trifluoroacetyl-, N-pentafluoropropionyl- and N-heptafluorobutylamino derivatives of the tripeptide valyl-alanyl-leucine have been synthesized in every combination with the carboxy derivatives O-methyl ester, O-(1-H,H)-trifluoroethyl ester, O-(1-H,H)-pentafluoropropyl ester and O-(1-H,H)-heptafluorobutyl ester. These 16 derivatives have been mass measured after negative ionization using a 10% CO2/Ar moderator gas mixture in an electron impact ion source of a VG-ZAB-2F mass spectrometer. The fragmentation behaviour of the peptide derivatives have been studied by negative linked-scan, negative mass-analysed ion kinetic energy and charge inversion mass spectrometry. Most detected sequence ions originate from N-terminal fragments. Recorded anion currents and linked-scan measurement have shown that fluoro residues at the C-terminus increase the intensities of sequence ions, whereas N-terminal perfluoroalkyl derivatives generate [M – HF]− and [M – 2HF]− ions. The abundances of these fragment ions increase with increasing molecular weight of the N-terminal residues. The best sequence information with intense anion currents has been recorded with the peptide derivative N-trifluoroacetylamino-O-hepatafluorobutyl ester.

A reaction window in double charge-transfer mass spectrometry

Endoergic ion/molecule reactions resulting in double electron capture are analysed within a simple curve-crossing model. A Landau-Zener-type treatment indicates the existence of a reaction window in the functional dependence of the double charge-transfer cross-section on the endoergicity of the overall process. Practical implications for charge-inversion mass spectrometry are discussed.