Evaluation of Q-TOF-MS/MS and multiple stage IT-MSn for the dereplication of flavonoids and related compounds in crude plant extracts

LC/MS/MS is becoming a very important tool for the on-line identification o f natural products in crude plant extracts. For an efficient use of this te chnique in the dereplication of natural products, a careful study of the pa rameters used to generate informative MS/MS spectra is needed. In this pape r the CID MS/MS spectra of ubiquitous flavonoids and related plant constitu ents have been systematically studied using hybrid quadrupole time of fligh t (Q-TOF) and ion trap (IT) mass analysers under various CID energy conditi ons. The results demonstrate that, if for hydroxylated flavonoids the CID M S/MS spectra generated on both instruments are similar, for partially metho xylated derivatives, important differences are observed hampering the creat ion of MS/MS databases exchangeable between instruments. Generally, fragmen ts issued from C-ring cleavage, corresponding to those classically reported , were recorded but they were more easily observed on a Q-TOF instrument wh ile losses of small molecules were favoured in IT-MS. MS/MS spectra recorde d in the positive ion mode were more informative than those obtained from n egative ions. For the assignment of flavonoids product ion spectra, on-line accurate mass measurement of all MS/MS fragments was obtained on the Q-TOF , while the multiple stage MSn capability of the ion trap was used to prove fragmentation pathways.