Organic Phosphorus Compounds in Aquatic Sediments Towards Molecular Identification with Mass Spectrometry

Abstract: Phosphorus (P) regulates trophic status in most aquatic systems. However, only bioavailable P contributes to primary production. In most lakes and shallow seas, mineralisation of sediment P into its bioavailable form and its release to the water column is important for maintaining primary production. Sediment organic P forms a substantial proportion of this P to be mineralised and can originate from different sources on land (farmland, forests, etc.) or from primary production in the lake. These organic P forms can thus be expected to have differing composition, degradability and recyclable P content.Knowledge of the chemical structure of sediment organic P compounds is scarce, mainly due to lack of appropriate analytical techniques. The commonly used 31P-nuclear magnetic resonance (31P-NMR) technique, only identifies P binding groups, so a mass spectrometric (MS) analysis method was developed that allows individual sediment organic P compounds to be identified.EDTA as pre-extractant resulted in the highest P yield in subsequent NaOH extraction. Extracted organic P compound groups were identified using 31P-NMR. For identification of specific P compounds with MS, a sample preparation method prior to electrospray tandem mass spectrometry (ESI-MS/MS) analysis was developed. Liquid chromatography (LC) with porous graphitic carbon prior to ESI-MS/MS enhanced sensitivity and selectivity, enabling several of the ions detected to be identified as nucleotides. 31P-NMR analysis showed P monoesters to be the most stabile P compounds throughout a lake sediment profile. The developed LC-ESI-MS/MS analysis method revealed that some monoester-P (nucleotides) were labile, while other P compounds increased in concentration with Baltic Sea sediment depth and were therefore considered stabile. Differences in patterns of P compounds detected were also shown depending on catchment characteristics in relation to Baltic Sea sediment age.For cost-effective management of eutrophication, knowledge of the sources of degradable organic P forms, contributing to internal loading, is needed. This thesis showed the developed LC-ESI-MS/MS analysis method to be a powerful analytical tool for this purpose.