Chlorins in a sedimentary mixture were characterized, without prior isolation of individual components, using electrospray ionization combined with ion trap mass spectrometry. Collision-induced dissociation in the atmospheric sampling interface and multi-step mass spectrometry (i.e. MSn where n 2) were used in order to obtain structural information about the macrocycle. Fragmentation pathways are proposed for different macrocycle types based on data from model chlorins. Three unknown chlorins (RMM = 888, 844 and 790) are assigned as having bacteriochlorophyll macrocycle types esterifled to unusual side-chains (i.e. dihydrophytol for the unknown with a bacteriopheophorbide a structure, phytol and an alcohol with a molecular mass of 242 u for the two unknowns with a proposed bacteriopyropheophorbide d structure).