Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Author: search.filters.author.Eroğlu, Ahmet EminDepartment: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Chemistry

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Now showing 1 - 7 of 7
  • Doctoral Thesis
    Development of Novel Solid Phase Extraction (spe) Sorbents and Solid Phase Microextraction (spme) Fiber Coatings for Determination of Endocrine Disrupting Compounds (edcs)
    (Izmir Institute of Technology, 2017) Demirkurt, Merve; Eroğlu, Ahmet Emin
    This thesis is composed of four chapters. In the first part of the study, molecularly imprinted polymer (MIP) was prepared as SPE sorbent for selective determination of BPA prior to HPLC DAD analysis. The adsorption capacity and selectivity of imprinted polymers were investigated. To improve the MISPE method, the parameters including pH of sample solution, adsorption time, amount of sorbent, desorption solvent were examined. The extraction efficiency of BPA imprinted polymer was investigated by using the spiked samples of ultrapure, drinking and tap water. The second part of the thesis was about determination of estrogen hormones. For this purpose, amino modified silica and molecular imprinted silica were prepared and their SPE performances were compared. The proposed methodology was validated through the analysis of real water samples. The preparation of MIP nanoparticles encapsulated in electrospun polystyrene fibers as the SPME fiber coating was the subject of the third part of the thesis. Developed fibers were used for selective extraction and analysis of parabens in water samples. The optimization parameters affecting the extraction and desorption of parabens were investigated. The validity of the proposed method was verified via spike recovery tests. Finally, fibers having amino functionality prepared by the sol-gel based electrospinning process were used for determination of BPA. The effect of solution pH, extraction time, agitation speed and ionic strength on the extraction performance were investigated. Validity was checked via the application of the proposed methodology on real samples.
  • Doctoral Thesis
    Development of Solid Phase Microextraction (spme) Fibers for Various Analytical Applications: (i) Selenium Speciation in Waters. (ii) Separation and Determination of Triclosan and Triclocarban in Waters
    (İzmir Institute of Technology, 2016) Ziyanak, Esen; Eroğlu, Ahmet Emin
    In the first part of this study, four selenium species namely selenite, selenate, selenomethionine and selenocystine in water samples were tried to be separated using single solid phase microextraction (SPME) fiber on the same chromatographic run. Bare silica fibers were immersed into agarose matrix containing nano zerovalent iron (nZVI), ceria (CeO2) or zirconia (ZrO2). After characterization of fibers sorption/desorption parameters were optimized and standard reference materials were used to validate the proposed method. Direct mode of SPME method was used to extract the analytes prior to their separation with HPLC and detection with ICPMS. The optimum conditions for the extraction of selenium species with nZVI-agarose fibers are obtained as extraction pH: 4.0, agitation speed: 700 rpm, extraction time: 60 min, desorption matrix: 10.0 mM citrate solution, desorption time: 30 min, solution temperature: 25 °C, ionic strength: no NaCl addition. In the second part of this study, same fibers were used to separate triclosan (TCS) and triclocarban (TCC) using HPLC-DAD. Among all fibers prepared, nZVI-agarose modified fibers demonstrated the best extraction performance. The optimum conditions for the extraction of TCS and TCC with nZVI-agarose fibers are obtained as extraction pH: 5.0 and 7.0, agitation speed: 400 rpm, extraction time 60 min, desorption matrix: % 90 methanol - %10 water (adjusted to pH 3.0 with acetic acid), desorption time: 30 min, ionic strength: no NaCl addition.
  • Doctoral Thesis
    Preparation of Novel Fiber Coatings for Solid Phase Microextraction of Flavonoids
    (Izmir Institute of Technology, 2014) Esen, Meral; Eroğlu, Ahmet Emin
    Many plant species contain flavonoids which are widely utilized in food, pharmaceutical and cosmetics industries as additives. Literature studies show that most of the earliest drugs were of plant origin. Application of flavonoids in many fields necessitates the development of new extraction and determination methods in various samples. In this study, three different types of solid phase microextraction (SPME) coatings were produced. The first one is baicalin- and imidazole-functionalized silica fibers via sol-gel method. Both manual and dip-coating were employed. The fibers were examined by SEM and the results show that dip-coating produced more homogeneous coatings. The second one is polystyrene templated monolithic silica. Then, it was functionalized with baicalin and imidazole groups. The last solid phase microextraction coating is molecularly imprinted silica. In this case, a sol-gel process was used to synthesize molecularly imprinted silica with tetraethoxysilane (TEOS) as the crosslinking agent, aminopropytriethoxysilane (APTES) as a functional monomer, quercetin as the template molecule, and AlCl3 as a Lewis acid. Characterization of baicalin-functionalized monolithic silica and molecularly imprinted silica was achieved by SEM, FTIR, TGA and elemental analysis. SPME process was followed by HPLCDAD at 335 nm after separation of flavonoids on a Zorbax Eclipse XDB-C18 (5μm, 4.6x150mm) column at 25.0°C with gradient elution using methanol and water (containing 0.10% acetic acid). Functionalized silica fibers were utilized in solid phase microextraction of apigenin, apigetrin, eriodictyol, isoquercitrin, luteolin, and quercetin. The results demonstrated that higher extraction efficiency can be obtained with baicalinfunctionalized monolithic silica and molecularly imprinted silica coated fibers.
  • Doctoral Thesis
    Use of Silica-Based Sorbents for Separation and Preconcentration of V (iv) and V (v)
    (Izmir Institute of Technology, 2010) Erdem, Aslı; Eroğlu, Ahmet Emin
    Vanadium is one of the essential trace elements for plants and animals. While it is beneficial for normal cell growth, it becomes toxic at high concentrations. In the present study, silica-based sorbents were prepared and used for sorption/speciation of vanadium from waters prior to inductively coupled plasma mass spectrometric (ICP-MS) determination. Among the sorbents developed, 3-APTES-modified silica, has been shown to be an efficient material for the speciation of vanadium. Solution pH of 2.0 and 3.0 can be used for the respective sorption of V(V) and the total vanadium, namely, V(IV) and V(V). The concentration of V(IV) can then be calculated from the difference. Desorption from the sorbent was realized with 0.5 M thiourea prepared in 0.2 M HCl. The validity of the method was checked via spike recovery experiments with four different types of water; namely, ultra pure, bottled drinking, tap, and sea water. The method works efficiently (>85% recovery) for ultra pure, bottled drinking, and tap water; and a relatively high recovery (>70%) was obtained even for sea water which has a very heavy matrix. For trypsin-immobilized silica, the sorption percentage towards V(IV) and V(V) is almost constant (>90%) within the pH range 4.0-8.0 which demonstrates the possibility of using this sorbent for the sorption of both vanadium species. The sorption of vanadate ion was investigated both from a kinetic perspective and also in terms of Freundlich, Dubinin-Radushkevich and Langmuir isotherm models; and Langmuir model was found to describe the sorption better for both of the functionalized silicas.
  • Doctoral Thesis
    Investigation of Carotenoid Contents of Various Microalgae by Chromatographis/Spectroscopic Methods
    (Izmir Institute of Technology, 2013) Erdoğan, Ayşegül; Eroğlu, Ahmet Emin
    Microalgae are the most important energy sources among microorganisms. Carotenoids, as important pigments and antioxidants, are produced by microalgae and are used both for health purposes and as natural colorants. There has been considerable research for the development, identification and determination of new strains of organisms to produce a variety of carotenoids. New methods for the isolation of carotenoids should be developed also for analytical purposes. This study aimed the biosynthesis of carotenoids from microalgae, (Prochlorococcus sp., Scenedesmus protuberans and Nitzschia sp.) their identification and quantification. It is known that some types of microalgae can produce high amount of carotenoids under different stress conditions while some others can produce carotenoids only under stress. For this purpose, cultivation conditions were optimized for the production of new or high value of carotenoids in the selected microalgal strains. Freeze-dried microalgae were extracted using different organic solvents and their carotenoid contents were investigated by high performance liquid chromatography (HPLC) and other chromatographic techniques such as liquid chromatography-mass spectrometry (LC-MS); in addition to (UV-VIS) spectroscopy. In green microalgae lutein (2.54 mg/g for Prochlorococcus sp. and 2.45 mg/g for Scenedesmus protuberans) is the most abundant carotenoid. On the other hand, in brown microalga fucoxanthin (6.58 mg/g for Nitzschia sp.) is the highly accumulated carotenoid. Under stress conditions, many microalgae alter their biosynthetic pathways for the formation and accumulation of carotenoids. Therefore, the effect of different nitrogen sources, oxidative stress conditions and different light sources on lutein content in green microalgae and on fucoxanthin content in brown microalga were investigated.
  • Doctoral Thesis
    Development of Novel Functionalized Solid Phase Extraction (spe) Sorbents and Solid Phase Microextraction (spme) Fiber Coatings for Analytical Applications
    (Izmir Institute of Technology, 2011) Boyacı, Ezel; Eroğlu, Ahmet Emin
    In the first part of the study, amino-, mercapto- and bifunctional silica-based solid phase extraction (SPE) sorbents were developed, characterized and utilized for sorption and speciation of inorganic As(III)/As(V). Critical parameters on sorption and desorption of species were investigated. The proposed methodology was validated through the analysis of a standard reference material. The subsequent studies were concentrated on the transfer of the experience gained during the modification of silicate surface for preparation of SPE sorbents to the preparation of SPME coatings. The second part of the thesis includes the development, characterization and use of solid phase microextraction (SPME) fibers for the speciation of inorganic and organometallic arsenic compounds. SPME fiber coatings have been prepared by two routes, namely, sol-gel synthesis and nanoparticle immobilization. Fibers having amino functionality synthesized through the sol-gel process were used in the speciation of As(III), As(V), monomethyl arsonic acid (MMA) and dimethyl arsinic acid (DMA). HPLC-HGAAS or HPLC-ICPMS was used in the measurements. Speciation of arsenic compounds was also realized using SPME fibers modified with zero valent iron nanoparticles embedded into an agarose matrix. The detection of the solid phase microextracted analytes was realized by HPLC-ICPMS. Prepared fibers have shown superior extraction for arsenicals. The effect of several parameters on the extent of extraction of arsenic species; namely, solution pH, extraction time, agitation speed and ionic strength were investigated. Validity was checked via the application of the proposed methodology on real samples (tap water, bottled water and geothermal water, urine samples) and standard reference materials.
  • Doctoral Thesis
    Development of Novel Sorbents for the Determination of Mercury in Waters by Cold Vaporatomic Absorption Spectrometry
    (Izmir Institute of Technology, 2011) Erdem, Arzu; Eroğlu, Ahmet Emin
    Mercury is one of the most toxic heavy metal ions to all living organisms. A novel solid support with selective functional groups was developed for mercury sorption from waters prior to its determination by cold vapor atomic absorption spectrometry. The support was prepared by immobilization of several functional groups (amino, mercapto, etc.) on silica. Among the sorbents developed, 3-MPTMS-silica has been shown to be an efficient material for the sorption of mercury species due to its selectivity. Sorption experiments were performed to optimize the necessary parameters and conclusively, sorption pH of 7.0, reaction temperature of 25 oC, sorbent amount of 10.0 mg and shaking time of 30 min were applied throughout the study. Various mineral acids, organic acids, oxidizing agents and sulfur- or nitrogen-containing ligands were tried for the elution of mercury species and 2.0 M TGA was found to offer the maximum desorption. The validity of the method was checked via spike sorption experiments with four different types of water; namely, ultra pure, bottled drinking, tap and sea water. The method worked efficiently (>95%) for all types of water. Permeable reactive barriers, such as zero-valent iron and zero-valent copper were also applied for the removal of mercury species. Similar optimization parameters with 3-MPTMS-silica were also obtained for both sorbents. The method validation was also performed and although sea water is a heavy matrix, high uptake results were achieved for both sorbents.