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1.
Effects of Photodegradation in TLS Measurements: Troubleshooting and Applications in Photochemistry and Photocatalysis
Mladen Franko, 2023, published scientific conference contribution abstract (invited lecture)

Abstract: Most analytical applications of thermal lens spectrometry (TLS) and related theoretical models consider absorbance of the sample constant during a single excitation by the pump laser beam. For photolabile analytes intensive excitation light can cause photodegradation, which significantly affects the results of TLS measurements. Theoretical models have been developed to account for changes in concentration and consequent changes in absorbance, caused by chemical reactions of different orders. Furthermore, abnormal TLS signal transients were observed for fast photochemical reactions on millisecond time scale, and the contributions of photodegradation as well as molecular diffusion were analyzed in detail. It has also been demonstrated that such effects can be reduced by performing TLS measurements in flowing systems such as in the case of flow injection analysis (FIA) or microfluidics. These findings were utilized to study the kinetics of chemical reactions, processes such as photostability of the soybean oil and thermal stability of biodiesel, or to improve the sensitivity of TLS detection in case of photolabile analytes. Furthermore, in combination with the concept of biomolecular recognition, FIA-TLS was exploited to study the efficiency of photocatalytic degradation of some neurotoxic substances such as organophosphate insecticides and revealed the formation of even more toxic degradation products. High sensitivity of TLS has enabled discrimination between photocatalytic and photosensitization mechanisms in photocatalytic degradation of textile dyes as well as between photodegradation and photocatalysis as will be demonstrated by the results of latest research in this field.
Keywords: Spektrometrija TLS, fotolabilnost, CrIVI), fotokataliza, fotorazgradnja
Published in RUNG: 23.10.2023; Views: 1275; Downloads: 0
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2.
Določevanje kroma(VI) v mikrofluidnem sistemu z optotermično mikroskopsko detekcijo : /
Sara Malovrh, 2015, undergraduate thesis

Abstract: Krom (Cr) spada med kovinske onesnaževalce, katerega učinek na okolje je močno odvisen od oksidacijskega stanja. Za ljudi je problematična njegova šestvalentna oblika Cr(VI), ki je rakotvorna, zato je potreba po hitri detekciji Cr(VI) velika. V diplomski nalogi smo preverjali točnost detekcije Cr(VI) ob prisotnosti različnih presežkov motečih elementov kot so šestvalentni molibden (Mo(VI)), petvalentni vanadij (V(V)), trivalentno železo (Fe(III)) in dvovalentno živo srebro (Hg(II)). Po kolorimetrični reakciji čistega standarda Cr(VI) in raztopin motečih elementov z difenilkarbazidom (DPC) smo za meritev uporabili spektrofotometrijsko metodo (SPEC) in mikroskopijo s toplotnimi lečami v mikrofluidnem sistemu za pretočno injekcijsko analizo (µFIA - TLM). Rezultati so pokazali, da največjo napako pri meritvah povzroči prisotnost V(V). Izvedli smo tudi študijo razpada preiskovanih kompleksov Cr-DPCO, Mo-DPCO, V-DPCO, Fe-DPCO in Hg-DPCO v odvisnosti od moči vzbujevalnega laserja v mikrofluidnem TLS sistemu (TLM). Dokazali smo, da je železov kompleks stabilnejši od ostalih preiskovanih ionskih kompleksov, ki so znani kot fotolabilni. Z izračunom spodnje meje določevanja (LOD) za SPEC in TLM metodo smo pokazali, da je TLM, zaradi nižje LOD vrednosti primernejša metoda za detekcijo nizkih koncentracij Cr(VI) v vzorcu. Analiza vzorcev iz Soče in Ljubljanice je prikazala sliko realnega stanja v, potencialno s Cr(VI), onesnaženi reki.
Keywords: spektrofotometrija, TLS, TLM, fotolabilnost, moteči elementi
Published in RUNG: 30.09.2015; Views: 6772; Downloads: 275
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