Določanje furanskih spojin v izolacijskih tekočinah na osnovi sintetičnih estrov

Matoh, Jan (avtor), Kralj Cigić, Irena (mentor), Gazvoda, Martin (komentor)

V okviru magistrskega dela sem razvil metodo za določanje furanskih spojin v transformatorskih izolacijskih tekočinah na osnovi sintetičnih estrov. Namen dela je bila ponovljiva kvantitativna določitev furanskih spojin v sintetičnem estru s komercialnim imenom MIDEL 7131. Najprej sem v literaturi poiskal podatke za določanje teh analitov s HPLC (tekočinska kromatografija visoke ločljivosti; angl. high performance liquid chromatography) metodo. Na osnovi literaturnih podatkov sem uporabil reverznofazno C18 kolono in izbral mešanico metanola in vode v razmerju 60:40 kot komponenti mobilne faze v gradientnem načinu s konstantnim pretokom 1 mL/min. Volumen injiciranja je bil 25 µL, valovni dolžini detektorja sem nastavil na 220 nm in 278 nm. Pred samo analizo na HPLC je bila potrebna še ekstrakcija analitov. Po obstoječi metodi za mineralna olja, ki v literaturi prevladuje, ta vključuje ekstrakcijo na trdno fazo (SPE). Ta način pa se je za vzorce izolacijske tekočine na osnovi sintetičnega estra MIDEL 7131 izkazal za neustreznega, saj je bil za štiri izmed petih analitov izkoristek ekstrakcije manjši od 10 %. Zato sem tekom optimizacije metode spreminjal tako različna topila za elucijo s SPE kartuš, kot tudi različna topila za mobilno fazo na HPLC, od katerih sem izbral mešanico vode in acetonitrila (ACN). Poskusil sem tudi ekstrakcijo tekoče-tekoče s kombinacijo različnih mešanic topil, ki z estrom tvorijo dvofazni sistem. Ugotovil sem, da je voda moteč faktor, v kolikor pride v stik z estrom. S pomočjo HPLC in jedrske magnetne resonance (NMR) sem potrdil, da ne potekajo reakcije med analiti in vodo ali razgradnimi produkti hidrolize estra. Pri kombinaciji vode in estra je težava topnosti ene faze v drugi, saj nastane emulzija. To je za namene priprave vzorca nezaželeno, zato sem v nadaljevanju ekstrakcijo tekoče-tekoče izvedel z dimetil sulfoksidom (DMSO), ki se je izkazal za primerno topilo. Nato sem z optimizacijo razmerja ester: DMSO, časa mešanja in kromatografskih pogojev dosegel zadovoljive izkoristke ekstrakcij ob hkratni dovolj nizki meji določitve (LOQ). Tri furanske spojine, 2-furfural (2-FAL), 2-acetilfuran (2-ACF) in 5-metilfurfural (5-MEF), je bilo možno kvantitativno določiti s HPLC po ekstrakciji tekoče-tekoče iz vzorcev z DMSO. V kasnejših fazah raziskave sem se osredotočil izključno na 2-FAL, saj velja za najbolj stabilnega izmed analitov in je zato prisoten v najvišjih koncentracijah. Za ta analit sem izrisal dve ločeni, delno prekrivajoči se kalibracijski krivulji, ki sta pokrivali nižje (0 – 0,3 µg/g) in višje območje (0,2 – 3 µg/g). Obe krivulji izkazujeta zelo dobro linearnost in ponovljive rezultate. Prav tako sta ponovljivo dali zelo podobne rezultate za standard v prekrivajočem se koncentracijskem območju. Poleg tega ima metoda nizko mejo določitve (LOQ), ki sem jo ocenil na 0,03 µg/g. To je posebej pomembno, saj so vsebnosti analitov v vzorcih sintetičnih estrov nižje kot v mineralnih oljih. Na ta način sem dokazal, da metoda uspešno omogoča kvantitativno določitev vsebnosti 2-FAL v transformatorskih izolacijskih tekočinah na osnovi sintetičnih estrov.

• Jezik: Slovenski jezik
• Ključne besede: furanske spojine, HPLC, ekstrakcija tekoče-tekoče, sintetični ester, transformatorji
• Vrsta gradiva: Magistrsko delo/naloga
• Tipologija: 2.09 - Magistrsko delo
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2026
• PID: 20.500.12556/RUL-183151
• COBISS.SI-ID: 283108867
• Datum objave v RUL: 05.06.2026

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Determination of furanic compounds in synthetic ester-based insulating liquids

Izvleček

Within this master’s thesis, I developed a method for determining furanic compounds in synthetic ester-based insulating liquids used in power transformers. The aim of this work was to quantify furanic compounds in the synthetic ester MIDEL 7131. Initially, I reviewed relevant literature to identify suitable HPLC (high performance liquid chromatography) methods for the determination of the target analytes. Based on the literature, I selected a reversed-phase C18 column as the stationary phase and a methanol–water mixture (60:40, v/v) as the mobile phase in gradient mode at a constant flow rate of 1 mL/min. The injection volume was 25 µL, and the detector wavelengths were set at 220 nm and 278 nm. Prior to HPLC analysis, extraction of the analytes from the synthetic ester was required. According to established methods for mineral oils, which predominate in the literature, this step typically involves solid-phase extraction (SPE). However, this approach proved unsuitable for the synthetic ester-based insulating liquid MIDEL 7131, as the extraction efficiency for four out of five analytes was below 10 %. Consequently, during method optimisation, I evaluated various elution solvents for the SPE cartridges as well as different mobile phase solvents for HPLC, of which I opted for mixture of water and acetonitrile (ACN). In addition, I investigated the possibility of using liquid–liquid extraction with different solvent mixtures that form a two-phase system with the synthetic ester. I found that water acts as an interfering factor when it interacts with the ester. Using HPLC and nuclear magnetic resonance (NMR) spectroscopy, I confirmed that no chemical reactions occur between analytes and water or products of ester hydrolysis. Regarding the mixture of water and ester, the issue arises from the mutual (in)solubility of the two phases, leading to the formation of an emulsion. As this is undesirable for sample preparation, I subsequently assessed liquid–liquid extraction using dimethyl sulfoxide (DMSO), which proved to be a suitable solvent. By optimising the ester-to-DMSO ratio, mixing time, and chromatographic conditions, I achieved satisfactory extraction efficiencies while maintaining a sufficiently low limit of quantification (LOQ). Three furanic compounds (2-furfural (2-FAL), 2-acetylfuran (2-ACF), and 5-methylfurfural (5-MEF)) were quantified by HPLC analysis after extraction from samples using liquid–liquid extraction with DMSO. In the later stages of the research, I focused only on 2-FAL, as it is considered the most stable analyte and is therefore present at the highest concentrations. For this analyte, I established two separate, overlapping calibration curves to cover both the lower (0 – 0.3 µg/g) and higher (0.2 – 3 µg/g) ends of the concentration range. Both curves showed exceptionally good linearity and produced repeatable results. Notably, they consistently yielded comparable results for a standard in the overlapping concentration region. Moreover, the method exhibits a low limit of quantification (LOQ), which I estimated to be 0.03 µg/g. This is especially important, as lower amounts of analytes are present in synthetic ester samples compared to mineral oils. Therefore, I showed that the method can be used to successfully determine the 2-FAL content in synthetic ester-based transformer liquids.

• Ključne besede: furans, high-performance liquid chromatography (HPLC), liquid-liquid extraction, synthetic ester, transformer