Innovative analytical methodologies based on ionic liquids for mercury determination in natural waters
- Autores: Gemma Elias Estañol
- Directores de la Tesis: Clàudia Fontàs Rigau (dir. tes.), Sergi Diez Salvador (codir. tes.)
- Lectura: En la Universitat de Girona ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Eric Guibal (presid.), Cristina Palet i Ballús (secret.), María Inés Gameiro (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología del Agua por la Universidad de Girona
- Materias:
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- Resumen
Water is an indispensable resource for living bodies, not only for consumption but also as a habitat. Since it is a scarce resource, it is important to control its quality. One of the main parameters of concern is the contamination of water by heavy metals such as mercury (Hg). This metal found in water may come from natural sources as well as from anthropogenic sources, such as fossil fuel combustion or urban waste incineration. Although Hg concentration in aquatic systems is usually low, the problem related to this metal is its biomagnification and bioaccumulation along the trophic web. Due to its high toxicity, analytical methodologies are needed to facilitate Hg determination and monitoring in natural waters at low concentration levels.
The investigation presented in this thesis is focused on the design of new analytical methodologies to allow Hg preconcentration using ionic liquids (IL) incorporated in functionalized membranes or impregnated onto solid sorbents.
To carry out this investigation, two ILs, trioctylmethylammonium salicylate (TOMAS) and trioctylmethylammonium tiosalicylate (TOMATS), have been prepared and characterized, and effectively incorporated into polymeric inclusion membranes (PIMs) using cellulose triacetate (CTA) as the polymer. Their extraction capacity has been evaluated. Membranes prepared with TOMATS, which contains a thiol group in its chemical structure, have proven to be highly effective for Hg extraction in different natural waters, without showing matrix effect, and at low concentration levels. This has allowed the development of an analytical methodology using a PIM with TOMATS as a medium for Hg extraction and the subsequent analysis of the membrane by means of Energy Dispersive X-ray Fluorescence (EDXRF). It has been demonstrated that this methodology enables the analysis of water samples at levels required by Council Directive 98/83/EC. It is also worth noting that this investigation has demonstrated that Hg extracted in a PIM is conserved for a long time period. Thus, these membranes are presented as a suitable medium for the preservation of the metal, enabling it to be detected not on immediate analysis without affecting its quality.
In addition, a new methodology has been designed with the PIM containing these ILs, consisting of the preconcentration of the metal present in water samples in a receiving phase of cysteine. This methodology has allowed the analysis of the sample by means of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), which require aqueous samples. It has been observed that the incorporation of a plasticizer in the PIM composition is necessary in order to allow the transport of Hg to the receiving phase, and different studies on the effect of the plasticizer’s characteristics on transport efficiency have been carried out. These studies have demonstrated that plasticizers with characteristics as different as nitrophenyl octyl ether (NPOE) and dibutyl sebacate (DBS), lead to very efficient membranes.
For the first time, a study on the possible biofilm growth onto a PIM surface made of CTA, TOMATS and NPOE has been performed. It has been proven that after seven days being soaked in a natural aquatic environment, the presence of biofilm was extremely scarce and the transport efficiency of the membrane was not affected. This fact is of paramount importance when designing Hg passive sampling systems.
Finally, the possibility of preparing impregnated sorbents with TOMATS for their use as a binding phase in samplers based on the Diffusive Gradient in Thin Films (DGT) technique has been studied in this thesis. Thus, two kinds of sorbents have been evaluated; one of an organic nature such as cellulose, and another inorganic one such as silica dioxide nanoparticles. Both materials have allowed impregnation and the obtaining of materials easy to manipulate and highly efficient for Hg extraction. Also, it has been proven that their inclusion in an agarose gel matrix did not affect their extraction efficiency and Hg elution was achieved using a cysteine solution. Last but not least, new DGT devices have been prepared using agarose as a diffusive phase and a new binding phase consisting of silica dioxide nanoparticles impregnated with TOMATS, which can be employed for Hg monitoring in natural aquatic systems.
