Optimizacija analiznih metod za fotorazgradne produkte PAH in ftalatnih estrov, adsorbiranih na mikroplastiko

Čubej, Katarina (author), Prosen, Helena (mentor)

Mikroplastika (MP) so delci manjši od 5 mm v premeru, ki nastanejo s fragmentacijo plastičnih odpadkov ali so proizvedeni kot primarna MP, in predstavljajo globalen okoljski problem. Zelo problematično je sproščanje strupenih dodatkov iz materiala ter vloga MP kot vektorja za organska onesnaževala, ki se v vodnem okolju adsorbirajo na hidrofobno površino MP preko hidrofobnih, elektrostatskih in nekovalentnih interakcij. Kapaciteta adsorpcije je odvisna od karakteristik MP, kemijskih lastnosti onesnaževala in pogojev v okolju. Prisotnost MP lahko povzroči nastanek različnih radikalov, ki vplivajo na fotorazgradne procese organskih spojin v rečni in morski vodi. Namen mojega raziskovalnega dela je bila optimizacija analiznih metod za fotorazgradne produkte, adsorbirane na MP, za dve skupini pomembnih okoljskih onesnaževal. Prva so ftalatni estri (dimetil in dibutil ftalat) in njihovi fotorazgradni produkti. Druga skupina pa policiklični aromatski ogljikovodiki – PAH (naftalen, acenaften, fenantren, fluoranten) in nekateri njihovi fotorazgradni produkti. Najprej sem optimizirala separacijsko metodo s tekočinsko kromatografijo visoke ločljivosti (HPLC-DAD) za mešanico vseh navedenih onesnaževal. Za namen predkoncentracije in čiščenja vzorcev ter menjave topila je bila optimizirana ekstrakcija na trdno fazo (SPE) za vsako skupino onesnaževal posebej. Raziskovala sem primerjavo med različnimi kolonami (LC-8 in HLB), elucijskimi topili (metanol in acetonitril v različnih razmerjih), ter vpliv koraka spiranja (Milli Q voda), pH (3,0 – 4,7) in ionske moči vzorca (dodatek NaCl). Optimizirano HPLC metodo sem prenesla na tekočinsko kromatografijo, skopljeno s tandemskim masnim spektrometrom (LC-MS/MS), kjer sem uporabila različne načine snemanja z namenom identifikacije razgradnih produktov. S končno metodo sem analizirala modelne vodne vzorce PAH, ki so vsebovali že desorbirane spojine z MP po obsevanju z UV svetlobo, ter modelne vodne vzorce dibutil ftalata, ki so bili obdelani z elektrooksidacijo. S pomočjo fragmentacijskih vzorcev sem uspešno predlagala identiteto nekaterih vrhov, pri čemer sem v obeh skupinah vzorcev opažala ponavljajoče se interference. Z dodatno visokoločljivostno MS analizo vodnih vzorcev sem potrdila strukture razgradnih produktov.

• Language: Slovenian
• Keywords: mikroplastika, policiklični aromatski ogljikovodiki, ftalati, fotorazgradnja, ekstrakcija na trdno fazo, LC-MS/MS
• Work type: Master's thesis/paper
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2024
• PID: 20.500.12556/RUL-164505
• Publication date in RUL: 28.10.2024

Secondary language

• Language: English
• Title: Optimisation of analytical methods for photodegradation products of PAH and phthalate esters adsorbed on microplastics

Abstract

Microplastics (MPs) are particles smaller than 5 mm in diameter, formed mostly by fragmentation of plastic waste or produced as primary MPs, and they present a global environmental pollution problem. Very problematic is the leaching of toxic chemical additives from the material and MPs’ capability to serve as vectors for organic pollutants in aquatic environment. Pollutants are adsorbed on the hydrophobic surface of MPs via hydrophobic, electrostatic, and non-covalent interactions. Adsorption capacity depends on characteristics of MPs, chemical properties of micropollutants, and environmental factors. The presence of MPs can generate different radicals that modify photodegradation of organic compounds in freshwater and seawater. The aim of this research was the optimization of analytical methods for photodegradation products adsorbed on MPs for two groups of important environmental pollutants. First group are phthalate esters (represented by dimethyl and dibutyl phthalate) and their photodegradation products. Second group are polycyclic aromatic hydrocarbons, PAH (naphthalene, acenaphthene, phenanthrene, fluoranthene) and some of their photodegradation products. A separation method was developed for mix of all pollutants listed above, using high-performance liquid chromatography (HPLC-DAD). For sample pretreatment, solid-phase extraction (SPE) was optimized for each group separately. Comparison of different columns (LC-8 and HLB), elution solvents (methanol and acetonitrile in different ratios), washing steps (Milli Q water), effect of sample pH (3.0 – 4.7) and ionic strength (addition of NaCl) were investigated. Finally, the optimized HPLC method was transferred to liquid chromatography – tandem mass spectrometry (LC-MS/MS). Different scan modes were used to identify the degradation products. The complete method was applied to model aqueous samples of PAH containing already desorbed compounds from MPs particles after UV radiation and model aqueous samples of dibutyl phthalate treated with electrooxidation. Based on fragmentation patterns I successfully proposed identity of some peaks. Interferences were observed in all the samples. With additional high-resolution MS analysis of PAH samples, I confirmed structures of the degradation products.

• Keywords: microplastics, polycyclic aromatic hydrocarbons, phthalates, photodegradation, solid phase extraction, LC-MS/MS