Optimisation of chromatographic methods for isolation of carboxyl rich alicyclics from dissolved organic matter

Jurečič, Luka (avtor), Prosen, Helena (mentor), Hawkes, Jeffrey (komentor)

Dissolved organic matter (DOM) is an extremely complex mixture of reduced organic compounds. It was shown to have a major impact on global carbon cycle, as well as to participate in distribution of organic pollutants and trace metals. Therefore, understanding the structure and function of DOM is imperative for applications such as water treatment and climate modelling. However, due to its inherent complexity, separation of species is not possible even with the most advanced analytical techniques. The project focused on the separation and enrichment of carboxyl rich alicyclic molecules (CRAM) from complex environmental samples. CRAMs are believed to be a major part of recalcitrant DOM. In the literature, it was shown that CRAM molecules have very few double bonds, with most of the hydrogens bound on fused aliphatic rings and oxygen atoms. Despite their importance for understanding the structure of natural DOM, sample CRAM molecules have never been synthesized, precluding the enrichment from natural samples. To tackle this problem from a well constrained direction, a group of newly synthesized CRAM compounds were used as a reference standard to enrich this complex class of molecules from a marine and terrestrial DOM sample. The main aim of the project was to optimize the high-pressure size-exclusion method for fractionation of DOM samples. The method was outlined according to the specifications of the high-pressure size exclusion chromatography (HPSEC) column. Optimal mobile phase composition (organic content and pH) was determined for HPSEC with charged aerosol detection (CAD) to separate two major classes of compounds: CRAMs and lignin. CAD chromatograms were processed using a code that was written in MATLAB to achieve a mathematical score of separation (resolution) between the CRAM and lignin reference standards. The developed HPSEC method was also used to fractionate DOM samples and on-line coupled electrospray ionisation high resolution orbitrap mass spectrometry was then applied to characterise the obtained fractions from a marine and terrestrial DOM sample. Cluster analysis was used to gain insight into the families of compounds that are present in the samples. These included Pearson’s Principal Coordinate Analysis and Van Krevelen cluster analysis.

• Jezik: Angleški jezik
• Ključne besede: dissolved organic matter (DOM), carboxyl rich alicyclic molecules (CRAM), size-exclusion chromatography, MATLAB, mass spectrometry
• Vrsta gradiva: Diplomsko delo/naloga
• Tipologija: 2.11 - Diplomsko delo
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2024
• PID: 20.500.12556/RUL-158453
• COBISS.SI-ID: 198718723
• Datum objave v RUL: 12.06.2024

Sekundarni jezik

• Jezik: Slovenski jezik
• Naslov: Optimizacija kromatografskih metod za izolacijo karboksilno bogatih alicikličnih spojin iz raztopljene organske snovi

Izvleček

Raztopljena organska snov (DOM) je zelo kompleksna zmes reduciranih organskih spojin. DOM ima močan vpliv na globalno kroženje ogljika, sodeluje pa tudi pri porazdeljevanju organskih onesnaževal in kovin. Zato je razumevanje molekulske sestave in funkcije DOM nujna pri drugih aplikacijah, kot so čiščenje komunalnih voda in podnebnem modeliranju. Vendar pa je zaradi kompleksnosti nemogoče ločiti med posameznimi skupinami spojin tudi z najnovejšimi analiznimi tehnikami. V diplomski nalogi sem se osredotočil na ločbo in obogatitev karboksilno bogatih alicikličnih spojin (CRAM) iz realnih okoljskih vzorcev. CRAM naj bi predstavljale velik del DOM, ki se nalaga v okolju. CRAM imajo večino vodikovih atomov vezanih v združenih alifatskih obročih z zelo malo dvojnimi vezmi, vsebujejo pa kisikove funkcionalne skupine. V literaturi še ni podatkov o sintetiziranih CRAM spojinah, ki bi bile uporabljene kot standardi pri izolaciji CRAM iz realnih vzorcev. V nalogi sem uporabil skupino novo sintetiziranih CRAM spojin kot referenčni standard za obogatitev teh spojin iz vzorca DOM iz morja in tal. Glavni cilj diplomske naloge je bila optimizacija visokotlačne velikostno-izključitvene kromatografije (HPSEC) za ločitev vzorcev DOM na različne frakcije. Mobilno fazo sem načrtoval glede na specifikacije velikostno-izključitvene kolone. Optimalno sestavo mobilne faze (delež organskega topila in pH) sem določil za HPSEC z detektorjem nabitih aerosolov (CAD) in tako ločil dve veliki skupini spojin: CRAM in lignin. Kromatograme sem analiziral s programom, ki sem ga napisal v programu MATLAB. Tako sem pridobil matematično vrednost ločbe (resolucije) med referenčnimi standardi za CRAM in lignin. Optimizirano HPSEC metodo sem uporabil za frakcionacijo realnih vzorcev DOM. HPSEC je bila sklopljena z masno spektrometrijo visoke ločljivosti z elektrorazprševalno ionizacijo in orbitrap analizatorjem za karakterizacijo frakcij iz vzorca DOM iz tal in morja. Uporabil sem »cluster« analizo (Pearson’s Principal Coordinate Analysis, Van Krevelen diagram) za interpretacijo masnih spektrov za določitev skupin spojin, ki so prisotne v vzorcih.

• Ključne besede: raztopljena organska snov (DOM), karboksilno bogate aliciklične molekule (CRAM), velikostno-izključitvena kromatografija, MATLAB, masna spektrometrija