Resumen de Espectrometria de masses d’alta resolució i mesura de massa exacta. Caracterització de la matèria orgànica dissolta en masses d’aigua naturals i tractades
Nuria Cortés Francisco
This thesis mainly focuses on the use of high resolution mass spectrometry (HRMS) and accurate mass (AM) measurements for the characterization of dissolved organic matter (DOM) in natural and affected environments. HRMS and AM measurements have been used for the characterization and determination of organic compounds in the environment. The first part of the thesis starts with a review of HRMS terminology, followed by the discussion of some parameters influencing AM measurements and the procedure for the identification of organic compounds when using HRMS. A description of the main mass analyzers capable of acquiring high resolution (HR) mass data and some environmental applications are also presented and discussed. Additionally, to evaluate the capabilities of new mass spectrometers a comparison was carried out. Different mass analyzers were tested during a single day of work for the analysis of small molecules in negative electrospray (ESI) mode. This study was necessary in terms of a timely update on the topic, as other comparative studies had been carried out some years ago. Furthermore, the present study focuses on a wider mass range (not only a single m/z) and the negative ESI was tested as there were almost no data on AM measurements in this mode. Moreover, the analysis of DOM is usually preferentially acquired in negative mode. Some of the main features were compared: resolution, exact mass determination, sensitivity, simplicity and calibration protocol. Due to the selectivity and specificity of HRMS, it is one of the techniques that has given more information about DOM at molecular level. Description of the methodology applied to DOM characterization is found in the second part of the thesis. The isolation of DOM from different water bodies and the use of different mass analyzers have been optimized, in order to present some alternatives to the methods already used in the literature. Moreover, structural information about marine DOM has been obtained based on a method using HR tandem mass spectrometry. DOM has a very important role in many environmental processes as it is present in all natural waters. DOM is not toxic by definition, however the presence of DOM can influence the solubility and fate of anthropogenic pollutants in the aquatic media. For instance, DOM can significantly affect the drinking water quality in terms of taste, color, odor, transportation of organic pollutants and water treatment process. DOM has been reported as disturbing the good performance of the water treatments and it is said to be a precursor of disinfection by products (DBPs) formation. For these reasons, knowledge of DOM is of importance in drinking water treatment processes. The last part of the thesis is focused on the use of the methodology described above for the characterization of DOM along different water treatment plants. The study mainly focuses on the changes of DOM through advanced treatments based on membrane technology: ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). Changes regarding the nature of DOM have been observed when the water is treated through the RO and NF membranes, whereas no effect of UF on DOM was detected. Moreover, a method was developed to characterize the DOM adsorbed on two dissimilar NF membranes. There is no information at molecular level about DOM causing fouling to the membranes and this study brings new insights on this field.
