The analytical characterisation of flavonoid photodegradation products: A novel approach to identifying natural yellow dyes in ancient textiles

In a previous study new compounds were detected from light-aged natural yellow (flavonoid) dyes on alummordanted wool. We have now developed a novel analytical technique - negative ion electrospray ionisation quadrupole ion trap tandem mass spectrometry (ESI QIT MS) - for further study and identification of characteristic flavonoid photodegradation products in lightaged historical textiles. The comparison between atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI) both in negative and positive ion mode showed that negative ion electrospray ionisation is the better ionisation method for the analysis of flavones and flavonols, specifically apigenin, quercetin, kaempferol, morin, fisetin and luteolin. Furthermore, the analysis of acid-hydrolysis extracts from dyed wool by negative ion electrospray mass spectrometry (ESI MS) provided complementary data to those obtained by photodiode array high performance liquid chromatography (PDA HPLC). The study of flavonoids by negative ion ESI QIT MS showed fingerprint patterns of breakdown peaks specific to each flavonoid. An example of the analysis of these breakdown patterns to provide structural information is also discussed.