Razvoj kromatografskih metod za spremljanje izbranih emergentnih onesnaževal

Šimenko Lalič, Tilen (avtor), Prosen, Helena (mentor)

V tem magistrskem delu sem se osredotočil na določevanje benzotriazolov in alkilfenolov, ki so nekatera izmed najbolj zastopanih emergentnih onesnaževal. Tovrstne spojine se množično uporablja v industriji, kmetijstvu in gospodinjstvih, kjer se jih med drugim dodaja k sredstvom za zaščito proti koroziji, detergentom in plastičnim izdelkom. Benzotriazole sem določeval v modelnih odpadnih vodah, ki so bile obdelane s postopkom elektrooksidacije in elektro-Fentonovim procesom. Pri slednjem je bilo preverjeno tudi, kako na njegovo učinkovitost vpliva izbira katode. Spojine sem določeval s tekočinsko kromatografijo in na podlagi pridobljenih rezultatov primerjal uspešnost posameznih procesov. Elektro-Fentonov postopek se je izkazal za učinkovitejšega od elektrooksidacije. Enourna obdelava je zadostovala za odstranitev 96% benzotriazola, po dveh urah pa spojin ni bilo mogoče več zaznati. Pri elektrooksidaciji je po 60 in 120 min ostalo približno 40 in 10 % spojine. Oba procesa sta bolje potekala pri pH 2 kot pri pH 4. Izbira katode iz grafitnega filca (polsti) se je izkazala za učinkovitejšo napram katodi iz nerjavečega jekla. Pri prvi se je v eni uri benzotriazol razgradil pod mejo zaznave, pri drugi pa je 7,6 % benzotriazola ostalo. Preizkušena je bila tudi elektrooksidacija pod bazičnimi pogoji, kjer sem ugotovil, da visoke in nizke pH vrednosti dajejo primerljive rezultate. Za določevanje izbranih alkilfenolov (4-terc-oktilfenol, 4-oktilfenol in 4-nonilfenol) sem razvil učinkovito metodo, ki je temeljila na predkoncentriranju analitov z ekstrakcijo na trdno fazo ter plinski kromatografiji, sklopljeni s tandemskim masnim spektrometrom. Zaradi nizke hlapnosti in visoke polarnosti je bilo spojine potrebno derivatizirati. V prvem koraku sem optimiziral pogoje ekstrakcije na trdno fazo, kjer sem določil ustrezno kolono, elucijsko topilo ter njegov volumen. Kolona s sorbentom C8 in elucija s 5 mL etil acetata sta bila izbrana kot najprimernejša. Ugotovil sem tudi, da nakisanje vzorcev na pH 3 in dodatek 2 % elektrolita izboljšata izkoristke ekstrakcije. Sledila je optimizacija derivatizacije, kjer sem preveril, kako na njeno učinkovitost vplivajo izbira derivatizacijskega topila, volumen derivatizacijskega reagenta ter čas reakcije. Kot derivatizacijski reagent sem uporabili BSTFA + 1 % TMCS. Derivatizacija je najbolje potekala z dodatkom 30 μL topila in 70 μL reagenta. Čas ene ure in sobna temperatura so zadostovali za popolno pretvorbo. Meje zaznave celokupne metode so znašale 5,19 ng/L za 4-terc-oktilfenol, 6,87 ng/L za 4-oktilfenol in 6,45 ng/L za 4-nonilfenol. Izkoristki ter ponovljivost celotnega postopka so za 4-terc-oktilfenol znašali 137,7 in 4,3 %, 113,8 in 3,5 % za 4-oktilfenol, ter 67,3 in 4,8 % za 4-nonilfenol.

• Jezik: Slovenski jezik
• Ključne besede: emergentna onesnaževala, benzotriazoli, alkilfenoli, ekstrakcija na trdno fazo, derivatizacija, plinska kromatografija – masna spektrometrija, napredni oksidacijski procesi
• Vrsta gradiva: Magistrsko delo/naloga
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2024
• PID: 20.500.12556/RUL-161259
• Datum objave v RUL: 09.09.2024

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Development of chromatographic methods for monitoring of selected emerging pollutants

Izvleček

In this master's thesis, we focused on determining benzotriazoles and alkylphenols, which are among the most prevalent emerging pollutants. These compounds are widely used in industry, agriculture, and households, primarily added to corrosion protection agents, detergents, and plastic products. We determined benzotriazoles in model wastewater treated with the electrooxidation process and the electro-Fenton process. For the latter, we also examined how the choice of cathode affect its efficiency. Compounds were determined using liquid chromatography, and the results were used to compare the effectiveness of individual processes. The electro-Fenton process proved to be more effective than electrooxidation. One hour of treatment was sufficient to remove 96% of benzotriazole, and after two hours, the compounds were no longer detectable. In electrooxidation, approximately 40% and 10% remained after 60 and 120 min, respectively. Both processes performed better at pH 2 than at pH 4. The choice of a graphite felt cathode proved to be more effective than a stainless steel cathode. The former degraded benzotriazole below the detection limit within one hour, while 7.6% of benzotriazole remained with the latter. The electrooxidation process was also tested under alkaline conditions, where it was found that high and low pH values give similar results. For the determination of selected alkylphenols (4-tert-octylphenol, 4-octylphenol, and 4- nonylphenol), we developed an efficient method based on solid-phase extraction for pre- concentration of analytes and gas chromatography coupled with tandem mass spectrometry. Due to their low volatility and high polarity, the compounds needed to be derivatized. In the first step, we optimized the solid-phase extraction conditions, determining the appropriate cartridge, elution solvent, and its volume. The C8 sorbent cartridge and elution with 5 mL of ethyl acetate were selected as the most suitable. We also found that acidifying the samples to pH 3 and adding 2% electrolyte improved extraction efficiency. Next, we optimized the derivatization process, examining how the choice of derivatization solvent, volume of the derivatization reagent, and reaction time affected its efficiency. BSTFA + 1% TMCS was used as the derivatization reagent. Derivatization worked best with the addition of 30 μL of solvent and 70 μL of reagent. One hour at room temperature was sufficient for complete conversion. The detection limits of the entire method were 5.19 ng/L for 4-tert-octylphenol, 6.87 ng/L for 4- octylphenol, and 6.45 ng/L for 4-nonylphenol. The recovery and repeatability of the entire process were 137.7% and 4.3% for 4-tert-octylphenol, 113.8% and 3.5% for 4- octylphenol, and 67.3% and 4.8% for 4-nonylphenol.

• Ključne besede: Emerging pollutants, Benzotriazoles, Alkylphenols, Solid-phase extraction, Derivatization, Gas chromatography – mass spectrometry, Advanced oxidation processes