| Summary: | 碩士 === 國立臺北科技大學 === 化學工程與生物科技系化學工程碩士班 === 107 === High performance liquid chromatography was widely used to separate chiral mole
cules. Proper choice of sorbent and solvent modifier are specially important. In the normal phase, polysaccharide-based sorbent was widely used to recognize chiral molecules. The mobile phase often contains polar modifier which can affect the interactions between the solute and sorbent.
Recently, studies have investigated the effect of solvent on the recognition mechanism of polysaccharide-based sorbents, but it remains unclear how these modifier molecules affect solute retention behavior. This study was conducted into three parts. First, in pure hexane, we used four different columns: Chiralpak IA (amylose tris(3,5-dimethylphenylcarbamate))、IB (cellulose tris(3,5-dimethylphenylcarbamate))、IC (cellulose tris(3,5-dichlorophenylcarbamate))、IE (amylose tris(3,5-dichlorophenylcarbamate))
columns, to study the retention behaviors of different solutes. The functional group Cl on the phenyl group of the side chain can attract electrons, increasing the bonding strength of the NH group. Benzene has π − π interaction with phenyl group of the sorbent, but the Cl group of the side chain can interfere electron cloud of the phenyl group. The π − π interaction was weakened because of Cl group interactions.
Second, this study investigates how the modifiers affect the adsorption behavior. By fitting different isotherm models to the adsorption data, the data of acetone in Chirapak IA、IB、IC columns were discovered to follow the Langmuir isotherm. Bi-Langmuir isotherm and Langmuir-Freundlich isotherm more accurately fit the IE data, which means the adsorption was heterogenous. By fitting different isotherm models to the IPA adsorption data, the sorbents IA and IC were discovered to follow the Langmuir isotherm. Bi-Langmuir isotherm, Freundlich isotherm, and Langmuir-Freundlich isotherm more accurately fit the IB and IE data.
Third, the retention behaviors of the solutes were investigated adding the isopropanol modifier in the mobile phase. When increasing isopropanol concentration, the retention factors of methanol and tert-butyl alcohol decreased. This phenomenon is due to the competitive adsorption behaviors. Because the binding sites of acetone and isopropanol are different, so the presence of the isopropanol didn’t affect acetone adsorption very much.
Because the IC and IE sorbents have Cl group, the bonding strength of the acetone was stronger than that in the IA and IB sorbents. When isopropanol was used as the polar modifier, U-shaped retention curves were obtained for all aromatic solutes. The aromatic interactions were inferred to include both electrostatic and dispersion interactions. When the modifier concentration was low, electrostatic interaction was the main contribution. In contrast, when the modifier concentration was high, the dispersion interaction was the
main contribution.
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