RAZVOJ ELEKTROKEMIJSKE METODE ZA PRAĆENJE POLISULFIDA (Sx2-) U MORSKOM EUKSINSKOM OKOLIŠU

doctoral thesis

• Title (english): DEVELOPMENT OF AN ELECTROCHEMICAL METHOD FOR MONITORING POLYSULFIDES (Sx2-) IN MARINE EUXINIC ENVIRONMENT
• Author: Sarah Mateša Đureković
• Mentor: Irena Ciglenečki-Jušić (mentor)
• Committee member: Zrinka Ljubešić (predsjednik povjerenstva)
• Committee member: Dario Omanović (član povjerenstva)
• Committee member: Suzana Šegota (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Geology); Zagreb
• Defense date and country: 2024-10-25, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Interdisciplinary Natural Sciences; Marine Science
• Universal decimal classification (UDC): 55 - Geology. Meteorology. Hydrology

Abstract

Direktno analitičko određivanje polisulfida (Sx2-) u vodenim otopinama predstavlja izazov zbog niskih konstanti termodinamičke stabilnosti Sx2-. S ciljem razvoja i primjene direktne metode za određivanje i karakterizaciju Sx2-, istraživano je njihovo elektrokemijsko ponašanje na živinoj (Hg) elektrodi. Morski euksinski okoliš Rogozničkoga jezera – Zmajeva oka (RJ) izabran je kao model za ispitivanje elektroanalitičke metode (EM), difercijalno pulsne voltametrije (DPV) za direktno određivanje polisulfida u prirodnim uvjetima. Za praćenje reduciranih sumpornih specija (RSS), odnosno Sx2- uz DPV, korištene su i ciklička voltametrija (CV) i stepenasta DC voltametrija/polarografija (SDC), ali i druge analitičke metode: UV/Vis spektrofotometrija za dodatno određivanje Sx2-, te mikroskopija atomskih sila (eng. atomic forced microscopy, AFM) i dinamičko raspršenje svjetlosti (eng. dynamic light scattering, DLS) za praćenje promjene svojstava RSS. AFM-om je praćena promjena morfologije stanica fototrofnih sumpornih bakterija kao izvora elementarnog S pri različitim okolišnim i eksperimentalnim uvjetima, dok je s DLS praćena promjena hidrodinamičkog radijusa elementarnog S u različitim uvjetima razrjeđenja. DPV metodom određeni su Sx2- u modelnim otopinama, te u RJ s najvećim koncentracijama u uzorcima ispod kemokline. Praćenjem sezonske dinamike Sx2- pokazano je kako njihova prisutnost i koncentracija ovise o fizikalno – kemijskim i mikrobiološkim čimbenicima. Najveće koncentracije, do 89 μM polisulfidnog S0, određene su tijekom ljeta za vrijeme izraženije raslojenosti vodenog stupca i intenzivnije mikrobiološke aktivnosti kada su dominirale ljubičaste sumporne bakterije (eng. purple sulfur bacteria, PSB), dok tijekom slabije raslojenosti i pojave holomiksije, Sx2- nisu detektirani.

Abstract (english)

The direct analytical determination of polysulfide (Sx2-) in seawater solutions is a challenge due to the low thermodynamic stability constants of Sx2-. To develop and apply a direct method for determining and characterizing Sx2-, its electrochemical behavior was investigated at a mercury (Hg) electrode. The marine euxinic environment of Lake Rogoznica – Zmajevo oko (RL) was chosen as a model for testing the electroanalytical method (EM), differential pulse voltammetry (DPV) for the direct determination of polysulfides under natural conditions. In addition to DPV, cyclic voltammetry (CV) and sampled DC voltammetry/polarography (SDC) were also used to monitor reduced sulfur species (RSS), i.e. Sx2-, as well as other analytical methods: UV/Vis spectrophotometry for additional determination of Sx2- and atomic force microscopy (AFM) and dynamic light scattering (DLS) to monitor changes in RSS properties. The change in cell morphology of phototrophic sulfur bacteria as a source of elemental S under different environmental and experimental conditions was monitored by AFM, while DLS monitored the change in hydrodynamic properties of elemental S under different dilution conditions. The DPV method was used to determine Sx2- in model solutions and the RL water column, with the highest concentrations measured in samples below the chemocline. The observation of the seasonal dynamics of Sx2- showed that its presence and concentration depend on physico-chemical and microbiological factors. The highest concentrations, up to 89 μM polysulfide S0, were determined in summer during pronounced stratification of the water column and intense microbial activity when purple sulfur bacteria (PSB) predominate, while Sx2- was not detected during periods of weak stratification and occurrence of holomixia.

• Keywords: elektroanalitičke metode; diferencijalno pulsna voltametrija; polisulfidi; reducirane sumporne specije; euksinski uvjeti; Rogozničko jezero - Zmajevo oko
• Keywords (english): electroanalytical methods; differential pulse voltammetry; polysulfides; reduced sulfur species; euxinia; Rogoznica Lake – Dragons eye
• Language: croatian
• URN:NBN: urn:nbn:hr:217:884041
• Promotion: 2025
• Project: Number: IP-2018-01-1717; Title: Rogozničko morsko jezero kao model odziva ekosustava na promjene u okolišu; Acronym: MARRES; Leader: Irena Ciglenečki-Jušić; Jurisdiction: Croatia; Funder: Hrvatska zaklada za znanost; Funding stream: Research Projects
• Study programme: Title: DOCTORAL STUDY OF OCEANOLOGY; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti u području prirodnih znanosti (doktor/doktorica znanosti u području prirodnih znanosti)
• Type of resource: Text
• Extent: 138 str., 30 cm
• File origin: Born digital
• Access conditions: Embargoed access; Embargo expiration date: 2025-11-01
• Created on: 2025-01-30 08:06:00