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- Patriarca, Claudia, et al.
(författare)
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Investigating the Ionization of Dissolved Organic Matter by Electrospray
- 2020
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 92:20, s. 14210-14218
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Tidskriftsartikel (refereegranskat)abstract
- Electrospray ionization (ESI) operating in the negative mode coupled to high-resolution mass spectrometry is the most popular technique for the characterization of dissolved organic matter (DOM). The vast molecular heterogeneity and the functional group diversity of this complex mixture prevents the efficient ionization of the organic material by a single ionization source, so the presence of uncharacterized material is unavoidable. The extent of this poorly ionizable pool of carbon is unknown, is presumably variable between samples, and can only be assessed by the combination of analysis with a uniform detection method. Charged aerosol detection (CAD), whose response is proportional to the amount of nonvolatile material and is independent from the physicochemical properties of the analytes, is a suitable candidate. In this study, a fulvic acid mixture was fractionated and analyzed by high-pressure liquid chromatography–mass spectrometry in order to investigate the polarity and size distributions of highly and poorly ionizable material in the sample. Additionally, DOM samples of terrestrial and marine origins were analyzed to evaluate the variability of these pools across the land–sea aquatic continuum. The relative response factor values indicated that highly ionizable components of aquatic DOM mixtures are more hydrophilic and have lower molecular weight than poorly ionizable components. Additionally, a discrepancy between the samples of terrestrial and marine origins was found, indicating that marine samples are better represented by ESI than terrestrial samples, which have an abundant portion of hydrophobic poorly ionizable material.
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| 2. |
- Patriarca, Claudia, 1986-
(författare)
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Characterisation of natural dissolved organic matter with liquid chromatography and high resolution mass spectrometry
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dissolved organic matter (DOM) is one of the most heterogeneous and complex mixture on Earth. DOM plays a crucial role in biogeochemical processes on the global scale and it is essential to sustain and regulate the biological processes in aquatic ecosystems. DOM originates from a multitude of biological, physical and chemical transformations, leading to its phenomenal chemical diversity. In order to understand and predict its effect on the global carbon cycle, an intimate characterization at molecular level is necessary. The investigation of the extraordinary complexity of the DOM mixture represents a compelling challenge for analytical chemistry. The focus of this thesis was the development of methods for the characterization of DOM in natural waters. High resolution mass spectrometry (HRMS), was combined with high pressure liquid chromatography (HPLC) and electrospray ionization (ESI), to investigate the chemical diversity of DOM. The first study demonstrated that cutting-edge techniques (such as the Fourier-transform ion cyclotron resonance mass spectrometer - FTICR-MS), are not indispensable to disclose essential information on the DOM molecular composition, in fact the Orbitrap mass analyser is a suitable alternative for the analysis of complex natural mixtures. In the second study, the potential benefits offered by the online coupling of HPLC and HRMS instruments were explored, revealing significant advantages in terms of analysis time, achievable information and versatility of the method. The advantages of online separation were further confirmed in the third study, focused on the characterization of autochthonous labile DOM. Chromatographically resolved profiles emerged from the bulk-DOM, allowing the monitoring of labile autochthonous components in presence of heterotrophic bacteria. Despite the advantages achieved by the application of online separation, a strong limiting factor in DOM characterization is the ESI source, suitable only for the analysis of the DOM fraction susceptible to ionization. In the last study, the extent of the DOM material prone to ionization was estimated, revealing the occurrence of an extensive portion of the material resistant to routinely employed ESI approach. The full characterization of DOM is still an open challenge and the combination of multiple techniques is fundamental to unravel is extreme intricacy.
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