Re-examination of the anion derivatives of isoflavones by radical fragmentation in negative electrospray ionization tandem mass spectrometry: experimental and computational studies - Vessecchi, R; Zocolo, G J; Gouvea, D R; Huebner, F; Cramer, B; de Marchi, M R; Humpf, H U; Lopes, N P (Rapid Commun Mass Spec, 2011)