61. Določevanje železa v naravnih vodah s tehniko FIA-TLSGaja Tomsič, 2019, master's thesis Abstract: Vodni organizmi potrebujejo železo za bistvene metabolne procese. Vendar pa se večina raztopljenega železa v vodi, ki ni vezana na organske molekule ali kompleksirana z anorganskimi ligandi, oksidira v železove ione Fe(III) in tvori oborino Fe(OH)3. Zato je aktivnost biomase na vodni gladini pogosto omejena z razpoložljivostjo raztopljenega železa, ki je lahko nižja od 1 nM. To dejstvo lahko vpliva tudi na širše okolje, saj ima vpliv na hitrost fiksiranja CO2 zaradi fotosinteze avtotrofne biomase. Določanje elementov v sledovih, med katerimi je tudi železo, predstavlja zaradi kompleksnosti naravne vode izziv. Določitev koncentracije železa je v preteklosti zahtevala predhodno koncentracijo vzorca z ekstrakcijo s topilom. V tem delu poročamo o rezultatih spektrometrije s toplotnimi lečami s pretočno injekcijsko analizo, ki ne potrebuje predkoncentracije železa v vzorcu.
Koncentracije železa v različnih redoks oblikah smo določali s pretočno injekcijsko analizo (FIA) z uporabo 1,10 - fenantrolina, ki kompleksira železove Fe(II) ione v stabilen kompleks z absorpcijskim maksimumom pri 508 nm. Skupno količino raztopljenega železa (Fe(II) in Fe(III)) smo določili po redukciji Fe(III) iona v Fe(II) z askorbinsko kislino. V sistemu FIA smo za detekcijo uporabili spektrometer s toplotnimi lečami (TLS); tipalni žarek je imel valovno dolžino 633 nm, vzbujevalni pa 450 nm ali 530 nm. Posledica absorpcije svetlobe vzbujevalnega žarka je segrevanje vzorca zaradi neradiacijske relaksacije absorbirane energije. Tvori se toplotna leča (TL). Detekcija temelji na razprševanju tipalnega žarka na TL. Analize vzorcev smo izvajali v »šaržnem« in »on-line« načinu. Z »on-line« konfiguracijo (1,10 - fenantrolin je sestavljal nosilno raztopino za FIA) smo lahko injicirali vzorce brez kakršnekoli predhodne priprave ali dodajanja reagentov, razen askorbinske kisline pri določevanju skupnega železa.
V tem magistrskem delu smo primerjali spodnje meje detekcije (LOD) različnih tehnik in pogojev (valovne dolžine laserske svetlobe in koncentracija nosilne raztopine v pretočnem sistemu) s ciljem, da bi dosegli najboljšo občutljivost za železove ione. FIA-TLS je primerna tudi za tehniko standardnega dodatka. Uporabnost in pravilnost FIA-TLS smo preverili z določevanjem koncentracij železa v rečni vodi.
Keywords: železove zvrsti, pretočna injekcijska analiza (FIA), spektrometrija s toplotnimi lečami (TLS)
Published in RUNG: 19.02.2019; Views: 4905; Downloads: 140
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62. Optimization of DGT technique for determination of iron species in natural water and sediments by photothermal beam deflection spectroscopyHanna Budasheva, Arne Bratkič, Dorota Korte, Mladen Franko, 2018, published scientific conference contribution abstract Keywords: beam deflection spectroscopy, diffusive gradients in thin-film technique, iron redox species, photothermal techniques, natural water, sediments
Published in RUNG: 23.11.2018; Views: 3775; Downloads: 0
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64. Photocatalytic properties of metal modified TiO2 by photothermal techniquesZeinab Ebrahimpour, Olena Pliekhova, Humberto Cabrera, Dorota Korte, Urška Lavrenčič Štangar, Mladen Franko, 2018, published scientific conference contribution abstract Keywords: Thermal lens spectrometry, Photothermal beam deflection spectroscopy, Dye remediation, Photothermal technique, Photocatalytic degradation, Reactive Blue 19, TiO2 modification
Published in RUNG: 09.11.2018; Views: 3690; Downloads: 0
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67. Rapid and Sensitive Determination of ChE Activity in Blood PlasmaAndrej Jerkič, Tjaša Birsa, Mojca Žorž, Dorota Korte, Martina Bergant Marušič, Mladen Franko, 2018, published scientific conference contribution abstract Keywords: flow injection analysis, thermal lens spectrometric detection, acetylcholinesterase, butyrylcholinesterase, enzyme activity
Published in RUNG: 16.07.2018; Views: 4335; Downloads: 0
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69. The detection and study of biologically active compounds in environmental processes and samplesMojca 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: 4932; Downloads: 247
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70. Hemichrome Determination by Thermal Lensing with Polyethylene Glycols for Signal Enhancement in Aqueous SolutionsViktoriya Galimova, Mladen Franko, Mikhail Proskurnin, Mingqiang Liu, 2018, original scientific article Abstract: The thermal lens technique is proposed for the determination of total hemoglobin in the form of reversible hemichrome. The conditions were optimized (concentration of sodium dodecyl sulfate, 2 mM) to attain the maximum sensitivity with the use of polyethylene glycols as signal enhancers. For polyethylene glycols with molecular weights 1500–35000 Da in a concentration range of 5–15% w/w (5–25 mM), the influence on thermal lens signal enhancement was estimated. It is shown that the use of 5% w/w polyethylene glycol 2000 provides the maximum increase in the thermal lens enhancement factor (by 40%) in comparison with unmodified aqueous solutions. The detection limit of iron(II) tris(1,10-phenanthrolinate) as a model system is 60 nM. Under these conditions, the thermal lens detection limit of hemichrome is 10 nM, which shows a 15-fold enhancement compared to spectro- photometry. Modification of the medium with polyethylene glycols decreases the limit of detection of hemichrome determination by 15% in comparison with unmodified aqueous solutions due to better reproducibility for the range of concentrations from 0.02 to 0.9 μM.
Keywords: Hemoglobin, hemikrom, optotermična spektroskopija, etilenglikol, spektrometrija s toplotnimi lečami
Published in RUNG: 16.04.2018; Views: 4101; Downloads: 0
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