MASS-SPECTROMETRY AND REVERSE-PHASE HPLC TECHNIQUES FOR THE IDENTIFICATION OF DEGRADED FOSSIL PIGMENTS IN LAKE-SEDIMENTS AND THEIR APPLICATION IN PALEOLIMNOLOGY

Accurate identification of fossil pigments is essential if they are to be used as biomarker compounds in palaeolimnological studies. In rece nt years High Performance Liquid Chromatography (HPLC) has greatly enh anced the efficiency with which fossil pigments can be characterised a nd quantified. Using HPLC,undegraded pigments are typically identified through retention times, absorbance spectra and co-chromatography wit h authentic reference standards. However, lake sediments may also cont ain degraded pigments for which there are often no standards, and whic h may be difficult to identify using HPLC alone. In this study, we sub mitted HPLC fractions of fossil pigments and pigment derivatives colle cted from a meromictic lake in south west Tasmania, to a combination o f Mass Spectrometry (MS) techniques including Electron Impact (EI) and static Liquid Secondary Ion MS (LSIMS) to identify their molecular io n characteristics and organic chemical composition. Mass Spectrometry permitted the detection of specific mass ions which were used to verif y the identity of pigments and their derivatives. These included five carotenoids, chlorophyll a and derivatives, three previously described bacteriochlorophyll c derivatives with molecular weights of 770, 784, and 802, and two undescribed derivatives of bacteriochlorophyll c wit h molecular weights of 766 and 788. With these improved identification s we speculate on the pathways and modes of pigment degradation in the lake and asses the value of the degraded pigments as biomarkers. The use of MS permitted the identification of a greater number of signatur e pigments of algal and bacterial communities thus increasing the pala eolimnological value of the sediments. These methods are best applied in fossil pigment studies where there are a large number of unknown pi gments and pigment degradation products, and where there are no authen tic standards for co-chromatography Practical suggestions for pigment MS are included in the discussion.