amicitia

How to get pure pheophytin a from plant leaves using thin-layer chromatography? I have tried different methods and extracted what I believe to be Pheo a (correct spectrum at room temperature), but it keeps degrading into two substances with very similar spectra (peaks have shifted about 2nm). Unfortunately I do not have access to a mass spectrometer so I do not know what these new substances are. I originally extracted with acetone, then tried ethanol and methanol, but it didn't change a thing. Any ideas? I don't mind reading about methods I have already tried, I'm just trying to make sure I am not re-inventing a bicycle here ;-)