This dissertation consists of seven chapters, which addresses the synthesis and applications of a new class of inexpensive and pure ionic liquids. Previously synthesized ionic liquids absorb UV light in the wavelength range important for chromatographic analyte detection. Moreover, the viscosities are too high for practical application using a standard liquid chromatography (LC) pump. We have demonstrated that alkylammonium carboxylates have the potential to be effective organic solvent replacements for reversed-phase LC.
A new low melting ionic liquid, ethylammonium acetate (EAA), which is a hygroscopic semi-solid that turns to a viscous liquid at 50°C, was synthesized. Chromatographic characterization of a 2.3 M EAA solution as a replacement for the organic solvent in the LC mobile phase was shown on four different columns, using various probe molecules. Alkylammonium formates ionic liquids, RNH3+ [HCO2-], R=C2H5, C3H7, C4H9 were prepared in high yield and purity by reacting an alkylamine and formic acid. The dried liquids were used as reference standards to determine the physical and chemical properties of the AAF. Chromatographic properties were also evaluated. Compared to propylammonium formate (PAF) and butylammonium formate (BAF), ethylammonium formate (EAF) has low UV cut-off and viscosity of only 11 Cp, very low for an ionic liquid.
The chromatographic characterization of EAF was done using a polystyrene-divinyl benzene column. Solvent strength (S) values averaged 2.1 and 2.4 for EAF and MeOH respectively. Van Deemter plots showed a similarity in plate count using EAF at 50°C as compared to methanol at room temperature. Resolution of nitrophenol isomers was enhanced using EAF as compared to methanol. EAF was effective in controlling the retention of solutes under totally aqueous mobile phase conditions. In order to improve the resolution of ionic compounds, the use of ion-pair reagents and EAF was explored. EAF with millimolar levels of either a cationic or anionic surfactant enhanced resolution of the corresponding oppositely charged organic acids or amines. First time use of polymerized surfactant poly (sodium-N-undecenoyl glycinate) in ion-pair LC was also demonstrated. The polarity, P’ of EAF (6.4) is higher than acetonitrile (5.8) and methanol (5.1), hence it was a milder mobile phase modifier that lessened the degree of protein denaturation for particularly lysozyme.