| 1. |
- De Brabandere, Heidi, 1980-
(författare)
-
Organic Phosphorus Compounds in Aquatic Sediments : Towards Molecular Identification with Mass Spectrometry
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
|
|
| 2. |
- Co, Michelle, 1975-
(författare)
-
Pressurised Fluid Extraction of Bioactive Species in Tree Barks : Analysis using Hyphenated Electrochemical Mass Spectrometric Detection
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Analytical chemistry has developed throughout time to meet current needs. At present, the interest in biorefinery is growing, due to environmental awareness and the depletion of fossil resources. Biomass from agricultural and forestry industries has proven to be excellent raw material for different processes. Biorefinering valuable species such as bioactive species from biomass, without compromising the primary process of the biomass is highly desirable. Pressurised fluid extraction (PFE) using water and ethanol as a solvent was developed for extracting betulin from birch (Betula pendula) bark. Apart from betulin, stilbene glucosides such as astringin, isorhapontin and picied were also extracted from spruce (Picea abies) using PFE. PFE is an advanced technique that extracts at temperatures above the solvent’s atmospheric boiling point. The applied pressure in PFE is mainly to maintain the liquid state of the extraction solvent. Parameters such as type of solvent, temperature, and time affect the extraction selectivity and efficiency. Therefore it is necessary to comprehend these parameters in order to optimise extraction. The DPPH (1,1-diphenyl-2-picrylhydrazyl) assay was used to determine the antioxidant capacity and activity of the obtained bioactive species. The results showed high antioxidant capacity in bioactive species that were extracted at an elevated temperature, 180°C. Extraction and degradation occur simultaneously during the extraction. Hence, it is crucial to separate these two processes in order to obtain the actual value. An online hyphenated system of chromatographic separation electrochemical mass spectrometric detection was developed (LC-DAD-ECD-MS/MS). The electrochemical detector facilitates real-time monitoring of the antioxidant capacity and activity of each antioxidant and its oxidation products. This developed LC-DAD-ECD-MS/MS method enabled rapid screening of antioxidants and created a fingerprint map for their oxidation products. Characterisation and molecular elucidation of bioactive species were also performed. Degradation of bioactive species was investigated with the said online system and birch bark extract was compared with birch bark extracts that were hydrothermally treated. The obtained results showed some degradation of antioxidants at 180°C. In summary, the aim of this thesis was to develop analytical methods integrated with sustainable chemistry for extraction of bioactive species in biomass from the forestry industry. A novel online system using selective and sensitive detectors such as diode-array, electrochemical, and tandem mass spectrometry was developed to rapidly determine the antioxidant capacity and activity of antioxidants. Furthermore, tandem mass spectrometry enables identification of unknown bioactive species without the need of reference samples.
|
|
| 3. |
- Paraskova, Julia V.
(författare)
-
Organic phosphorus speciation in environmental samples : Method development and applications
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the development of new methodology for the identification and quantification of organic phosphorus compounds in environmental samples.Phosphorus is a vital element for primary production and one of the factors contributing to eutrophication. Eutrophication of aquatic systems leads to algal blooms, changes in ecological balance and deteriorating water quality. Difficulties in studying organic phosphorus stem from the fact that organic phosphorus is present in the environment in a variety of forms and each form may have different degradation and turnover time, having very different effects on eutrophication.New methods for the quantification of phosphorus derived from three groups of organic phosphorus compounds were developed. For the determination of phosphorus derived from DNA and phospholipids selective extraction was combined with digestion and colorimetric determination of the extracted phosphate. For quantification of inositol phosphates high performance liquid chromatography was coupled with tandem mass spectrometry using electrospray ionization. The methods were applied to studying the distribution of these compounds in a small catchment and in the case of DNA-P and phospholipid-P, the degradation of the fractions in lake sediments. The studies showed that phosphorus bound to DNA, phospholipids and inositol phosphates constitute a sizeable part of the total phosphorus in different environmental samples. The phospholipid-P fraction was the smallest one, accounting for, on average, only a few percent of the total phosphorus in the sample. Inositol phosphates were most prevalent in the soils, with inositol hexakisphosphate accounting for over 10% of the total phosphorus content. The highest content of DNA-P was found in sediments and it was shown that DNA-P degrades more rapidly than phospholipid-P and therefore plays a more critical role in internal loading.
|
|
