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Opis: Environmental pollution is one of the greatest challenges that the world is facing today. Toxic compounds, such as pesticides, allergens, pharmaceuticals, toxins and heavy metals are widely present in the air, water and soil, and can affect the health of people and animals even in small quantities, as well as they may cause long- or short-term damage in plants [Hill, 1997]. Heavy metals (mercury, arsenic, cadmium…) are widely spread in the environment. They derive from a number of sources, including mining, industrial wastes and vehicle emissions [Tchounwou et al., 2012]. They are easily incorporated into biological molecules and exert their toxic effects by displacing essential metals of a lower binding power in biologically active molecules or by acting as noncompetitive inhibitors of enzymes, affecting neurological, reproductive, renal and hematological systems [Sunil D’Souza et al., 2003; Heavy-Metal Pollution, 2018]. Metals form countless compounds (e.g. metal complexes and organometallic compounds) which are essential for living organisms (vitamin B12, hemoglobin, chlorophyll) and/or have a wide range of applications in industry and other areas, including analytical chemistry. Because of the potential risk which toxic metals represent to the living organisms and also because of the importance of some essential metals, different analytical techniques and detection methods have been developed for studies of their occurrence, fate and concentration in the environment and in organisms. However, providing a required sensitivity for determination and speciation of different metals and their compounds, especially in small- volume samples is still a challenge. Therefore, general objectives of this dissertation were development of novel analytical methods for sensitive, reliable and fast determination of metal species, based on highly sensitive optothermal technique thermal lens spectrometry (TLS), which can be used as detection tool following colorimetric reaction of a selected metal ion or for direct detection of colored organometallic compounds. This dissertation is composed of the following chapters: introduction, research goals, theoretical background, results and discussion, conclusion and references. The core of this dissertation is presented in the fifth chapter (results and discussion), which is divided into three parts. They separately cover development of methods for determination of iron redox species, pyoverdine and Fe-pyoverdine complexes and mercury. Pyoverdine is a siderophore, excreted by a certain bacteria in order to scavenge iron in the environment and is closely related to the chemistry of iron in such biological systems. Therefore, the first two parts are closely related. Procedures for batch mode thermal lens microscopy (TLM), flow-injection thermal lens sprectrometry (FIA-TLS) and µFIA-TLM (flow injection and TLS detection in microspace) were developed for Fe(II) and Fe(III) determination, based on colorimetric reaction of Fe(II) with 1,10-Phenanthroline. All these procedures were focused on cloudwater examination with a tendency to minimize sample consumption but at the same time preserve low limits of detection (LOD) and limits of quantification (LOQ). TLM measurements with highly collimated probe beam were performed in a 100 μm optical path length cell (40 µL volume), which resulted in a considerably smaller sample volume requirement (500 µL in total) and consumption, as compared to UV-Vis spectrophotometry, which required at least 25 mL of sample due to large volume (almost 30 mL) of the 10 cm optical path-length sample cell. LODs for mode-mismatched TLM were 0.16 and 0.14 µM for Fe(II) and Fe(total) (sum of Fe(II) and Fe(III) concentrations), respectively, while LODs for UV-Vis spectrophotometry were 0.01 µM for both Fe(II) and Fe(total). By using the mode mismatched TLM we were able to detect concentrations corresponding to absorbances as low as 1.5 × 10-5, while the lowest absorbance detectable on the UV-Vis spectrophotometer corresponded to 1.1 × 10-3, despite the use of the 10 cm optical path-length cell. Another important step in the development of new methods for Fe(II) and Fe(III) determination was the use of TLS detection in FIA (FIA-TLS). By injecting 50 µL of the sample into the FIA-TLS system, cca. 10 times lower LODs were achieved (1 × 10-3 µM for Fe(II) and 8 × 10-4 µM for Fe(total)), as compared to the UV- Vis spectrophotometry. Nevertheless, the development of μFIA-TLM method, with on-line colorimetric reaction for Fe(II) and Fe(III) determination is considered as the most important achievement of this study. The results show that despite 100 times shorter optical path length and low sample consumption (3 µL of each sample/injection) compared to UV-Vis spectrophotometry, LODs for µFIA-TLM were 0.10 and 0.07 μM for Fe(II) and Fe(total) respectively, which is sufficiently for cloudwater analysis, since concentrations, lower than 0.1 μM are not expected [Parazols et al., 2006; Deguillaume et al., 2014]. Linear range for Fe(II) and Fe(III) determination by μFIA-TLM was between 0.1 and 70 µM. To test the accuracy of this method, artificial cloudwater was prepared, spiked with different amounts of Fe(II) and Fe(III) and analyzed for iron content by µFIA-TLM and UV-Vis spectrophotometry. Good agreement was observed between the two methods. To ascertain the ruggedness of the method 7 (or more) replicate determinations at two different concentrations for both, Fe(II) and Fe(total) in artificial cloudwater were carried out on day 1 (replicates were measured instantly after fortification), day 2 and day 5. A student’s t-test (p=0.05) was applied to compare 3 sets of obtained data (day 1, day 2 and day 5) and showed that sets are not significantly different from each other. Considering very low sample volume requirement of µFIA-TLM, this should be the method of choice for determination of Fe(II) and Fe(III) in investigations of processes in cloudwater, where multiparameter analysis is desired (determination of other ions, ligands, microbial counts, etc.). When larger sample volumes are available, FIA-TLS can be used for accurate determination of iron species at lowest concentration levels. High performance liquid chromatography (HPLC) was applied for separation and detection of pyoverdine (PVD), produced by Pseudomonas fluorescens 36b5, a bacterial strain isolated from the aqueous phase of clouds at the Puy de Dôme station (1465 m, France). Reversed-phase (RP) chromatography (RP-18 chromatographic column Hypersil gold), hydrophilic interaction liquid chromatography (HILIC) (ZIC®-Hilic column) and three different detection systems (diode-array (DAD), spectrofluorimetry (FLD) and TLS) were tested for their performance in separation and determination of pyoverdines and corresponding complexes of pyoverdine with iron (Fe(III)-PVDs). PVDs and Fe(III)-PVD complexes could not be separated and quantified by applying HILIC technique, therefore it was concluded, that HILIC is not suitable for HPLC-DAD and also not for HPLC-TLS, since the method should offer a simultaneous sensitive detection of free PVDs as well as Fe(III)-PVD complexes in a single chromatographic run. Since pyoverdine standards were available only as a mixture of several different forms of PVDs, whereby the exact composition was unknown, the quantification of each of the four major specie (two fluorescent PVDs and two nonfluorescent Fe(III)-PVDs) in the standard, which was obtained from Université Clermont Auvergne, Institut de Chimie de Clermont-Ferrand, was performed. When applying Hypersil gold column, a linear correlation between fluorescence intensity and absorbance of each component was observed in a concentration range 3–24 µg/mL, whereby LODs were estimated to be 0.03–0.04 µg/mL for each of the major PVD species (HPLC-DAD). Even though HPLC-FLD method provided cca. 100 times lower LODs, it is not the method of choice for determination of PVD species in cloudwater, because it does not allow detection of PVD complexes with Fe(III). When comparing HPLC-TLS and HPLC-DAD, LODs were 5 to 8 times lower in case of HPLC-TLS, which was a significant improvement. Furthermore, recoveries (89–111 %) at two concentration levels of four PVD species in two independent samples, showed good reliability of the method. Almost all mercury in uncontaminated drinking-water is thought to be in the form of Hg2+ [WHO, 2010]. Therefore, the method for Hg2+determination based on colorimetric reaction with triamterene, described originally by Al-Kady and Abdelmonem was further investigated in this study, as well as the possibilities of application of this reaction for Hg2+ determination by TLS. The stoichiometry of the complex formation was determined by the method of continuous variations and saturation experiment, suggesting formation of the complex with the formula Hg2-triamterene. The obtained value of the molar absorption coefficient was 9988 Lmol-1cm-1 at 403 nm, which significantly contradicts the existing data in literature, which reports the molar absorption coefficient of 5.32 × 104 Lmol-1cm-1 [Al-Kady and Abdelmonem, 2013]. Even though the spectrophotometric results were not encouraging for triamterene as colorimetric reagent for Hg2+ determination, it was further investigated for its performance in TLS system. Fe(II)-1,10-phenanthroline (ferroin) was used for comparison, because it was well studied for TLS applications previously. The results showed that Hg2-triamterene in solutions was degraded when it was exposed to the light of the excitation beam. Due to the lower molar absorptivity than reported in literature, fotodegradation and unfavorable complex stoichiometry, triamterene was not confirmed as a suitable colorimetric reagent for highly sensitive Hg2+ determination by TLS. In summary, this dissertation investigates alternative approaches for analysis of metal complexes and organometallic compounds in small-volume environmental water samples. Methods, which were developed in this research, could potentially serve as improvements of existing technologies, to facilitate analysis of such samples, by offering simple handling of samples and superior sensitivity over the UV-Vis spectrophotometry.
Ključne besede: thermal lens spectrometry, thermal lens microscopy, high performance liquid chromatography, microfluidics, metal complexes, organometallic compounds, iron, pyoverdine, mercury
Objavljeno v RUNG: 05.09.2019; Ogledov: 5892; Prenosov: 167
Celotno besedilo (3,65 MB)

Opis: This work focuses on assessing the analytical capabilities of a new photothermal lens method based on the self-mixing effect to reliably measure metallic traces in water-ethanol solutions. We compare it with the conventional thermal lens scheme, considering the low detection limit and versatility. A theoretical model is presented to describe the laser power variations as a function of the photothermal parameters of the analyzed sample. The experimental results demonstrate that the laser intensity variations, induced by the external optical feedback, are governed by the photothermal lens effect. Measurements of Fe(II)-1,10-phenanthroline in water–ethanol solutions show a favourable correspondence and agreement with the theory. The low detection limits obtained by the two analytic techniques also agree very well. Nevertheless, our instrument presents advantages regarding compactness and simplicity, suggesting that this platform could be potentially useful as a robust analytical tool for metallic trace detection. In addition, calibration of the method is performed by measuring the so-called self-mixing constant.
Ključne besede: thermal lens, photothermal spectroscopy, self-mixing effect, trace detection
Objavljeno v RUNG: 05.04.2019; Ogledov: 4536; Prenosov: 0
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Ključne besede: Thermal lens spectrometry, Photothermal beam deflection spectroscopy, Dye remediation, Photothermal technique, Photocatalytic degradation, Reactive Blue 19, TiO2 modification
Objavljeno v RUNG: 09.11.2018; Ogledov: 4695; Prenosov: 0
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Ključne besede: flow injection analysis, thermal lens spectrometric detection, acetylcholinesterase, butyrylcholinesterase, enzyme activity
Objavljeno v RUNG: 16.07.2018; Ogledov: 5369; Prenosov: 0
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Opis: Environmental pollution in the 21th century still represents a global problem for human and animal health. Despite general awareness about released substances and their degradation products their fate and possibilities of removal are not well investigated. Even though the chemicals released are dispersed and diluted in water cycles, their poor biodegradability and/or strong accumulation can result in the intoxication of exposed organisms. Similarly, as a part of the environment, food can get contaminated by bioactive substances during different steps of preparation. Not only artificial compounds such as pesticides or pharmaceuticals, but also natural toxins enter the food chain and impact negatively on humans' and animals' health. In addition, the activity of some bacteria can influence the production of amines from amino acids after fermentation, to which the human body responds with several symptoms of intoxication. Several analytical methods for the determination of trace levels of broad range contaminants have been developed. Due to the largely robust, selective and sensitive features of the conventional (rearguard) techniques, they represent the first choice for analysing multiple organic compounds in frequently very complex matrices. However, screening (vanguard) methods are paving the way in the chemical analytics as a solution that provides simplicity and rapid analytical responses with binary (yes/no) answers. They require little or no sample treatment as well as more economically-efficient instrumentation. The combination of vanguard-rearguard analytical strategies hence offers a compromise between classical analytical figures of merit and productivity-related characteristics. In the first part of our research feasibility studies for the application of TLS and/or TLM in novel analytical methods for the determination of lipid-lowering drug atorvastatin and a mycotoxin ochratoxin A . The survey on atorvastatin performed spectrophotometrically has shown a decrease of ATV-sulpho-vanillin product at the wavelength of its maximum absorbance after dilution by organic solvent, which was investigated due to the possible increasing of the method sensitivity. As the predicted LODs that could be obtained by TLM (0.3 mg/L) could not reach the concentration of ATV usually present in the environment (ng/L-g/L) further experiments on this subject were therefore not justified. On the other hand, the ELISA assay for the determination of ochratoxin A was performed. In case of μFIA-TLM, the measurements were influenced by high background signal resulting in high LODs of TLM (470 pg/mL), which is known as a background limited technique. It was estimated that the LODs of standard ELISA assay could not be significantly improved, therefore no further research was conducted in this direction. In the second part of the dissertation, a sensitive rearguard system by coupling HPLC and TLS for the determination of biogenic amines in wine samples was developed. Putrescine, cadaverine, histamine and tyramine were separated and detected on a HPLC-TLS system after derivatization by dabsyl chloride. The method was optimized in terms of chromatographic conditions and in terms of TLS parameters. Also, the sensitivity of the newly developed method was evaluated by comparing the TLS detection with DAD detection in terms of LOD values, where TLS showed 3.6-fold improvement compared to DAD. Afterwards, the standard addition calibration was performed and evaluated for its recoveries (86−117%) in the determination of the four BAs. The applicability of the novel method was tested by the analysis of real white and red wine samples and by comparing the results to the standard HPLC-FL method and concentrations of BAs in wine samples were in good accordance. In addition, the dabsylated BAs showed better stability compared to the OPA derivatives as they have not lost the peak intensity after 17h of storage. In the third part, a vanguard system for detection of the overall biogenic amines concentration was developed by employing μFIA-TLM. Initially, NH4Cl standard solutions were applied in the indophenol reaction for batch mode, off-line μFIA-TLM and in an on-line indophenol formation for μFIA-TLM detection. By adding 50 % of EtOH to indophenol we obtained 9-fold improvement. In addition, indophenol showed good stability under TLM conditions. We optimized the microfluidic and TLM parameters in the off-line and on-line indophenol reaction. The addition of 5% ethanol to the reagent in the on-line reaction resulted in the 3-fold improvement of the signal-to-noise ratio. Further on, the overall reaction, including the enzymatic and the following indophenol reaction, was optimized by choosing the optimal buffer (pH=7, 0.5 M) and alkaline conditions (2M NaOH). The influence of interferences from amino compounds was also evaluated and discussed. The off-line and on-line μFIA-TLM were evaluated by their performance characteristics. The LOD for ammonia detection reached 2.3 μM and the applicability in ammonia detection in water samples was discussed. Similar LOD of 3.2 μM was obtained for the overall concentration of BAs and LOD of 3.8 μM for histamine, which is more than 4-folds lower value as the lowest suggested limits of intake for histamine in wine samples (2 mg/L; 18 μM). Finally, an immobilization procedure on magnetic nanoparticles was developed for the possible implementation of the selected enzyme in a miniaturized biosensor.
Ključne besede: thermal lens spectrometry, thermal lens microscopy, high performance liquid chromatography, microfluidics, biogenic amines, microbial transglutaminase, indophenol (Berthelot) reaction
Objavljeno v RUNG: 04.06.2018; Ogledov: 7272; Prenosov: 251
Celotno besedilo (2,90 MB)
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