Charge remote fragmentation of fatty acids cationized with alkaline earth metal ions.

Fatty acids can be collisionally activated as [M - H + Cat](+), where Cat is an alkaline earth metal, by using tandem mass spectrometry. High-energy collisional activation induces charge remote fragmentation to give structural information. In the full scan mass spectra molecular ions are easily identified, particularly when barium is used as a cationizing agent; ions are shifted to a higher mass, lower chemical noise region of the mass spectrum. Moreover, the isotopic pattern of barium is characteristic, and the high mass defect of barium allows an easy separation of the cationized analyte from any remaining interfering ions (chemical noise), provided medium mass-resolving power is available. An additional advantage is that most of the ion current is localized in [M - H + Cat](+) species. Structural analysis of fatty acids can be performed when the sample size is as low as 1 ng.