Negative atmospheric pressure chemical ionisation low-energy collision activation mass spectrometry for the characterisation of flavonoids in extracts of fresh herbs

The flavonoid composition of commonly eaten fresh herbs such as dill, oregano and parsley was analysed by combined LC, MS and low-energy collision induced dissociation (CID) MS–MS. Negative atmospheric pressure chemical ionisation (APCI) MS and MS–MS were used to provide molecular mass information and product-ion spectra of the glycosyl compounds. The most prominent fragment was found to arise from the aglycone ion, which provides molecular mass information about the glycosyl substituent and the aglycone. Product-ion spectra of the aglycone verified the identity by comparison with product-ion spectra of authentic standards. Methoxylated flavonoids provide characteristic fragmentation, i.e., loss of ·CH3, which add to the usefulness of the method for identifying unknown flavonoids. Negative-mode APCI-MS is thus demonstrated to be a good alternative to the commonly employed positive mode operation.