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Opis: In this work, in-plane and through-plane thermal diffusivities and conductivities of a freestanding sheet of graphene nanoplatelets are determined using photothermal beam deflection spectrometry. Two experimental methods were employed in order to observe the effect of load pressures on the thermal diffusivity and conductivity of the materials. The in-plane thermal diffusivity was determined by the use of a slope method supported by a new theoretical model, whereas the through-plane thermal diffusivity was determined by a frequency scan method in which the obtained data were processed with a specifically developed least-squares data processing algorithm. On the basis of the determined values, the in-plane and through-plane thermal conductivities and their dependences on the values of thermal diffusivity were found. The results show a significant difference in the character of thermal parameter dependence between the two methods. In the case of the in-plane configuration of the experimental setup, the thermal conductivity decreases with the increase in thermal diffusivity, whereas with the through-plane variant, the thermal conductivity increases with an increase in thermal diffusivity for the whole range of the loading pressure used. This behavior is due to the dependence of heat propagation on changes introduced in the graphene nano-platelets structure by compression.
Ključne besede: graphene nanoplatelets, thermal diffusivity, thermal conductivity, photothermal spectrometry
Objavljeno v RUNG: 30.11.2021; Ogledov: 1792; Prenosov: 65
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Ključne besede: cyanobacteria, nanobodies, fluobodies, phage display, thermal lens spectrometry
Objavljeno v RUNG: 19.04.2021; Ogledov: 2187; Prenosov: 0
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Opis: In this work, a recently proposed thermal lens instrument based on multi-pass probe beam concept is investigated and described as a multi-thermal-lens equivalent system. A simulation of the photothermal lens signal formation in a multi-thermal-lens equivalent configuration of the system is performed and validated by comparing the experimental signals of single, dual and ten-pass configurations to theoretically calculated values. The theoretically predicted enhancement of the signal is 9 to 10-fold for a weak thermal lens when comparing the ten-pass configuration with the conventional single-pass thermal lens system. Experimentally achieved signal enhancement in the ten-pass system is 8.3 for pure ethanol sample and between 8 and 9 for solutions with different concentrations of the Fe(II) - 1,10-Phenanthroline complex. Additionally, a value of 9.1 was calculated as the ratio of the slopes of the calibration lines obtained using the ten-pass and single-pass configurations. The achieved limit of detection for determination of Fe(II), in the ten-pass configuration, was 0.4 µgL-1, with a relative standard deviation around 4.5%, which compares favorably with previously reported results for TLS determination of Fe(II) in thin samples using low excitation power. For the multi-pass configuration the linear range of measurement is reduced when compared to the single-pass configuration. This is explained by the theoretical analysis of the photothermal signal under multi-pass condition, which shows the important contribution of the nonlinear term in the theoretical expression for the photothermal signal. The ten-pass configuration, which is presented and validated experimentally for the first time, offers important signal enhancement needed in recently developed TLS instruments with tunable, low power excitation sources.
Ključne besede: Thermal lens spectrometry, Photothermal detection, Trace determination, Chemical sensor
Objavljeno v RUNG: 10.12.2019; Ogledov: 3181; Prenosov: 0
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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: 4258; Prenosov: 155
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Opis: ∂13C values of a suite of halocarbons have been determined in an urban background site in Bristol, UK. A novel mobile preconcentration system, based on the use of multi-adsorbent sample tubes, has been developed for trapping relatively large-volume air samples in potentially remote areas. An Adsorption Desorption System-Gas Chromatography-Electron Capture Detector was used to measure the mixing ratios of the selected halocarbon species, while a Gas ChromatographyCombustionIsotope Ratio Mass Spectrometer was used to determine ∂13C values. For the species with strong local sources, the variation of isotope ratios has been observed over the experimental period. Some of the results reported in the present study differ from previously reported values and reasons for this are discussed. The reporting of different ∂13C values for selected halocarbons from different areas in the present study suggests that ∂13C values may be used to determine the relative magnitudes of anthropogenic and biogenic sources.
Ključne besede: Adsorption Desorption System (ADS), Automated Thermal Desorber (ATD), Electron Capture Detector (ECD), Gas Chromatography (GC), Isotope Ratio Mass Spectrometry (IRMS)
Objavljeno v RUNG: 18.07.2019; Ogledov: 3097; Prenosov: 0
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