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1.
Recent progress and applications of thermal lens spectrometry and photothermal beam deflection techniques in environmental sensing
Mladen Franko, Leja Goljat, Mingqiang Liu, Hanna Budasheva, Mojca Žorž, Dorota Korte, 2023, original scientific article

Abstract: This paper presents recent development and applications of thermal lens microscopy (TLM) and beam deflection spectrometry (BDS) for the analysis of water samples and sea ice. Coupling of TLM detection to a microfluidic system for flow injection analysis (µFIA) enables the detection of microcystin-LR in waters with a four samples/min throughput (in triplicate injections) and provides an LOD of 0.08 µg/L which is 12-times lower than the MCL for microcystin-LR in water. µFIA-TLM was also applied for the determination of total Fe and Fe(II) in 3 µL samples of synthetic cloudwater. The LODs were found to be 100 nM for Fe(II) and 70 nM for total Fe. The application of µFIA-TLM for the determination of ammonium in water resulted in an LOD of 2.3 µM for injection of a 5 µL sample and TLM detection in a 100 µm deep microfluidic channel. For the determination of iron species in sea ice, the BDS was coupled to a diffusive gradient in the thin film technique (DGT). The 2D distribution of Fe(II) and total Fe on DGT gels provided by the BDS (LOD of 50 nM) reflected the distribution of Fe species in sea ice put in contact with DGT gels.
Keywords: thermal lens microscopy, beam deflection spectrometry, microfluidic system, microcystin-LR detection, iron species determination, ammonium detection
Published in RUNG: 03.01.2023; Views: 1217; Downloads: 24
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2.
The detection and study of biologically active compounds in environmental processes and samples
Mojca Žorž Furlan, doctoral dissertation

Abstract: 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.
Keywords: thermal lens spectrometry, thermal lens microscopy, high performance liquid chromatography, microfluidics, biogenic amines, microbial transglutaminase, indophenol (Berthelot) reaction
Published in RUNG: 04.06.2018; Views: 4838; Downloads: 247
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3.
Determination of bioactive compounds in food samples by thermal lens microscopy
Jelena Topić, Mojca Žorž, Valeria Guzsvány, Branka Mozetič Vodopivec, Dorota Korte, Mladen Franko, 2016, published scientific conference contribution abstract

Keywords: thermal lens microscopy, food samples, bioactive compounds
Published in RUNG: 08.11.2016; Views: 5393; Downloads: 0
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