Fig. 2. Ionophore challenge of E. modestus generates a number of A₂₀₀ UV-absorbing species, as shown by the HPLC UV profile (A, top panel). Online analysis by negative ion electrospray mass spectrometry (A, bottom panel) highlights the presence of a species eluting at 16 min, which generates an intense M-H^– ion at m/z 351 (inset). (B) The electron impact mass spectrum of the O-trimethylsilyl ether methyl ester derivative confirms the identity as trioxilin A₄.