REICHSTÄDTER, M. Využití techniky difúzího gradientu v tenkém filmu v analýze potravin a v environmentální analýze [online]. Brno: Vysoké učení technické v Brně. Fakulta chemická. 2020.
Examiner’s Report on Doctoral Thesis Author: Ing. Marek Reichstädter Title of Doctoral Thesis: Application of Diffusive Gradients in Thin Films Technique in Food and Environmental Analysis Doctoral Thesis Examiner: Associate prof. Dr. Martin Urík, PhD. The aim of the presented doctoral thesis is scientifically sound and clear. It suggest development and application of diffusive gradient in thin-films (DGT) technique for simultaneous determination of mercury and some other trace elements in complex food matrices (fish sauce). This also includes synthesis, chemical characterization and performance evaluation of cysteine modified silica resins and some commercial resin-based binding gels as well. The chemical composition of biomolecule modified resin is inspired by biological systems, where cysteine rich metallothioneins are part of natural chelation detoxification pathways. Furthermore, this technique allows identification of labile fraction of hazardous metals and if successfully applied in food industry, it will provide new effective way for handling the extremely complex matrices of food products while being powerful enough to provide relevant data for risk assessments and law regulations regarding toxicants’ concentrations in foods. Thus, the significant contribution of this thesis to study field of Food Science is obvious. The ideas and statements in thesis are understandable and the quality of written English is relatively high, though the paper still contains minor errors. It is divided into nine chapters (this also includes curriculum vitae and list of author’s published papers) with informative literature review (Chapter 2) that provides an overview on trace metal toxicity and environmental chemistry, optical and electrochemical methods for analysis, and pre-treatments methods regarding speciation and fractionation. The final subsection highlights the principles and advantages of passive in situ sampling DGT technique. Although the chapter is successful in stating and explaining the relevant topics, I think that subsections describing the (2.2.4.2) advantages and (2.2.4.3.) application of DGT should be written more critically to identify the themes and debates in DGT community. This would help the reader to evaluate the contribution and significance of the suggested aims of the research more clearly in respect to author’s field study. The literature review is followed by aims and objectives of the study in Chapter 3, and description of the applied methods and materials in Chapter 4. The latter, surprisingly heavily referenced, also highlights the reasons behind experimental approaches. It clearly builds up on the previous expertise of research groups in Czechia and Belgium. This is particularly really well written chapter in a way that allows reproducing experiments easily, and enhances the understanding of experimental design and decisions for specific experimental conditions. Chapter 5 Results and discussion is divided into two parts: (1) synthesis and characterization of a new resins, and (2) application of commercially available and newly synthesized resins for trace elements determination in fish sauce. This chapter successfully reflects the goals and objectives of the thesis within three research papers (being under review or already published). While the first manuscript “Cysteine-modified silica resin in DGT samplers for mercury and trace metals assessment” optimizes the synthesis of two novel cysteine-based resins and evaluate their performance in comparison to 3-mercaptopropyl silica resin and routinely used Chelex-100, the other two manuscripts “Determination of mercury in fish sauces by thermal decomposition gold amalgamation atomic absorption spectrometry after preconcentration by diffusive gradients in thin films technique” and “Simultaneous determination of mercury, cadmium and lead in fish sauce using Diffusive Gradients in Thin-films technique” indicate the validity of DGT with Purolite S924 binding gel in combination with CV-AAS for determination of mercury in fish sauces and superiority of DGT techniques in comparison to standard microwave-assisted digestion method regarding food sample handling, and LOD and LOQ values for simultaneous determination of mercury, cadmium and lead in fish sauce, respectively. By highlighting the promising application potential of Purolite S924 and other novel synthesized resins for simultaneous trace metal determination in liquid food matrices using DGT, the author concludes his research outcomes in Chapter 6 and suggests some new challenges for field study of Food Science in Chapter 7, including determination of iodine in milk using DGT technique. Overall, the thesis is well written and structured; the research outcomes are interesting, compelling and presented in understandable way. In the presented thesis, the author has proved himself as an accomplished and creative young scientist and clearly showed the ability to conduct experiments, and evaluate and analyze the experimental data independently. He also provided analyzes and outcomes relevant to the field of his study. Therefore, the presented thesis fulfilled all standard scientific and law requirements (§47 odst. 4 Zákona o vysokých školách 111/1998 Sb.) and, thus, I recommend the work for doctoral defense in a field of study Food Science in programme Chemistry and Technology of Foodstuffs. Marek Reichstädter demonstrated creative ability in research of his field and the presented thesis meets all of the required standards for the dissertations in his research field. Bratislava, August 31, 2020 Martin Urík
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