On-line photo-derivatization with flow injection and liquid chromatography–atmospheric pressure electrospray mass spectrometry for the identification of indoles

Abstract

The application of on-line photochemistry with flow injection (FI) and liquid chromatography (LC) in conjunction with atmospheric pressure electrospray mass spectrometry (LC–APESI–MS) for the identification of similar indole derivatives is reported here. The photo-transformation of the indole compounds is strongly affected by the substituent groups on the aromatic and heterocyclic rings. Upon photolysis for 2.5 min, the mass spectrum of tryptamine (Try) which has no OH substituent on the aromatic ring does not differ greatly from that obtained without photolysis. However, after photolysis of serotonin (Ser) which has one OH group on C5 of the aromatic ring, the mass spectrum indicates the formation of dimers and higher molecular weight ions. The fragmentation pattern of 5-hydroxytryptophol (Phol) without photolysis resembles that of Ser with a base peak of m/ z 160. Upon photolysis using MeOH–H 2O (10/90), Phol is found to form a base peak at m/ z 375 (100%) and a major peak at m/ z 214 (66%) in addition to other ions with lower abundance. Melatonin (Mel) and tryptophan (Phan) upon photolysis are found to form high molecular weight ions with a relative low abundance. The mass spectrum of indole-3-acetic acid (Inaa) with on-line photolysis also shows different ions that are not formed without photolysis.