Development of a reverse-phase chromatographic separation model based upon Hansen solubility parameters

Diplomsko delo sestoji iz pregleda literature, v katerem so predstavljeni sodobni trendi in metode napovedovanja retencije v reverzno-fazni tekočinski kromatografiji. Navedeni so Hansenovi parametri topnosti z njihovo izpeljavo, uporabo in eksperimentalnim določanjem. Sledi teoretična izgradnja modela reverzno-faznih kromatografskih separacij na osnovi Hansenovih parametrov topnosti. Uvede in definira se termodinamski deskriptor. V okviru teoretičnih ab initio pristopov z uporabo teorije gostotnega funkcionala so izračunani teoretični UV-vis absorpcijski spektri analitov in njihovi kavitacijski volumni. S HPLC eksperimenti je ustvarjena podatkovna zbirka retencije treh homolognih dialkil ftalatov, na osnovi katerih so zgrajeni teoretični model, in manjša zbirka preostalih analitov, s katerimi preverimo napovedno moč modelov. Hansenovi parametri topnosti se lahko uporabijo za napovedovanje retencije le za posamezne analite. Skupni modeli, ki poskušajo posplošiti formalizem še na ostale analite, nimajo praktične napovedne moči. Tekom eksperimentalnega dela je identificirana anomalija v občutljivosti retencije na spremembo temperature in sestave mobilne faze. Pri molskem deležu 0,34 acetonitrila (ACN) v mobilni fazi se občutljivost na spremembo temperature nenadno zniža. Identificiran je trend obratno-sorazmerne odvisnosti vpliva temperature in spremembe sestave mobilne faze na zmanjšanje občutljivosti retencije – s povečanjem deleža ACN se vpliv temperature na občutljivost retencije manjša. Ugotovitve sledijo zgolj iz eksperimentalnih podatkov. Z uporabo modela večkratne linearne regresije, ob upoštevanju termodinamskega deskriptorja, temperature in celokupne adsorpcije ACN na stacionarno fazo kot neodvisnih spremenljivk, se ustvari najuspešnejši model, ki nepopolno opiše zaznano anomalijo. Predstavljena metoda napovedovanja retencije na osnovi Hansenovih parametrov topnosti je prva, ki uporabi tovrstne termodinamske parametre topnosti za modeliranje reverzno-faznih kromatografskih separacij. Zato je teoretična izgradnja modelne enačbe z rigorozno matematično obravnavo in sledečo statistično študijo povsem izvirno delo.The bachelor’s thesis is comprised of a literature review, which describes the modern trends in the prediction of retention in reverse-phase liquid chromatography. An introduction to Hansen solubility parameters, their derivation, applications and experimental determination is presented. It is followed by a theoretical model construction, based upon Hansen solubility parameters. The thermodynamic descriptor is introduced and defined formally. UV-vis absorption spectra and solute cavitation volumes are calculated using density functional theory ab initio approaches. HPLC experiments are conducted in order to obtain a retention database of three homologous dialkyl phthalates, which are used in the construction of theoretical models. A smaller retention database of different analytes is also obtained to explore the models’ predictiveness. Hansen solubility parameters can be used for retention prediction, but only for models built upon one analyte at a time. A group model, comprised of different analytes, which aims to generalize the predictivity of retention for different compounds, has no real predictive ability. During the experimental work, an anomaly was identified. At the molar fraction of 0,34 acetonitrile in the mobile phase, the sensitivity of retention in response to a change in temperature is suddenly lowered. Aside from that, a trend of inverse relationship in the sensitivity of retention as a function of temperature and mobile phase composition is identified, exclusively using experimental data. An increase in the amount of acetonitrile lowers the effect of temperature on the retention sensitivity. A multiple linear regression model, using the thermodynamic descriptor, temperature and the total adsorption of acetonitrile onto the stationary phase as independent variables, is identified as the best model but fails to fully explain the identified anomaly. The presented method for predicting retention based on Hansen solubility parameters is a novel approach, using established thermodynamic solubility parameters for modelling reverse-phase chromatographic separations. The theoretical construction, rigorous mathematical formulation and statistical evaluation of the model equation are therefore entirely original