Mass spectrometry of 3,5-and 4,5-dicaffeoylquinic acids and selected derivatives

The mass spectral properties of 3,5- and 4,5-dicaffeoylquinic acids (DCQAs) and selected derivatives were examined using electron ionization (EI), fas t atom bombardment (FAB) and electrospray ionization (ESI), EI analysis of the trimethylsilyl derivatives provides molecular mass (M-r) information, b ut the spectrum is dominated by fragment ions of the caffeic acid group; is omers cannot be differentiated using EI. FAB analysis, in both the positive and negative ion detection modes, provides M-r information on the free com pounds, but little fragmentation is observed using normal scan conditions. The FAB mass-analyzed ion kinetic energy spectroscopic analysis of the free compounds does, however, permit differentiation of the isomers, with 3,5-D CQA showing selective loss of water, a process not observed with the 4,5-is omer. Both EI and FAB provide M-r and some structural information when appl ied to the peracetate derivatives of the DCQAs. ESI of the DCQAs provides c onsiderably more structural information, especially in the negative ion det ection mode, and is the recommended method of analysis of the quinic acid e sters. M-r, information, identity of the ester groups and differentiation o f isomers are possible using ESI. Copyright (C) 1999 John Wiley & Sons, Ltd .