Recent advances and trends in the liquid-chromatography-mass spectrometry analysis of flavonoids

Flavonoids have elicited significant attention as a result of their importance in plants, their influence on the properties of natural-product derived commodities and especially as a consequence of their purported health benefits. Research in all of these fields relies heavily on accurate analytical data, and in this LC-MS has come to play an influential role by allowing relatively fast tentative identification and accurate quantification of low levels of flavonoids in a variety of matrices. The field has undergone rapid expansion in the last decade due to important developments in both HPLC and MS instrumentation, which nowadays allow much faster and more accurate analysis of flavonoids. This contribution aims to provide an overview of these developments and their application in flavonoid analysis since 2009. The discussion is focussed first on methodologies which provide improved LC separation of flavonoids in terms of speed and/or resolution, including ultra high pressure LC (UHPLC), monolithic and superficially porous phases, high temperature LC (HTLC) and comprehensive two-dimensional LC (LC×LC). The fundamental background relevant to each of these will be briefly outlined, as well as the implications and promise of their hyphenation to MS. Secondly, the possibilities and limitations of a range of the latest MS instruments available in combination with advanced LC analysis will be discussed, including ion trap, triple quadrupole, time-of-flight, Orbitrap, ion mobility and various hybrid instruments. Examples from the latest literature will be used to illustrate the performance gains achievable in flavonoid analysis by the hyphenation of advanced LC separation and high-end MS instrumentation.