A novel sedimentary transformation product of chlorophyll, purpurin-7 phytyl ester, has been identi®ed by atmospheric pressure chemical ionisation liquid chromatography mass-spectrometry in sediments from Lake Baikal, Russia, Loch Ness and Priest Pot, UK. This product of oxidative transformation is an intermediate on the transformation pathway leading to sedimentary aetioporphyrins and its occu...