Differentiation of isomeric flavone/isoflavone aglycones by MS2 ion trap mass spectrometry and a double neutral loss of CO.
The fragmentation behaviour of seven pairs of isomeric flavone/isoflavone aglycones (solely hydroxylated and/or methoxylated) was studied using ion trap mass spectrometry with atmospheric pressure ionisation (API, both electrospray and APCI) in the positive and negative ion modes. A major difference was found in the neutral loss of 56 u, which was a common feature of all isoflavones in API(+). It was identified as a double loss of CO by accurate mass tandem mass spectrometric (MS/MS) measurements using a hybrid quadrupole time-of-flight (Q-TOF) instrument. Fragmentation of daidzein with (13)C-isotope labelling of the carbon C2 showed that this double loss occurred from the central ring of the molecule. A mechanism for this selective fragmentation is given. Further isoflavone-specific fragmentations were used to develop a guideline for the identification of isoflavone structures. A software-based neutral loss scan of 56 u in the API(+)-MS(2) mode was applied to extracts of leaves of Lupinus albus and to soy flour. The structure elucidation guideline allowed identification of hydroxy and/or methoxy isoflavones. Structures could be confirmed for those available as reference compounds.
Kuhn
Fabian
F
Organic Analytical Chemistry, University of Basel, Neuhausstr. 31, CH-4057 Basel, Switzerland.
Oehme
Michael
M
Romero
Fernando
F
Abou-Mansour
Eliane
E
Tabacchi
Raffaele
R
D002248:Carbon Monoxide / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D005419:Flavonoids / Q000737:chemistry* / Q000302:isolation & purification; D005433:Flour / Q000032:analysis; D007202:Indicators and Reagents; D007529:Isoflavones / Q000737:chemistry* / Q000302:isolation & purification; D031297:Lupinus / Q000737:chemistry; D013058:Mass Spectrometry; D010936:Plant Extracts / Q000032:analysis; D018515:Plant Leaves / Q000737:chemistry; D013025:Glycine max / Q000737:chemistry
D005419:Flavonoids; D007202:Indicators and Reagents; D007529:Isoflavones; D010936:Plant Extracts; D002248:Carbon Monoxide