Date of Award

Spring 5-17-2014

Degree Type

Dissertation

Degree Name

PhD. Chemistry

Department

Chemistry and Biochemistry

Advisor

Dr. Nicholas H. Snow

Committee Member

Yuri V. Kazakevich, Ph.D

Committee Member

Sergiu M. Gorun, Ph.D

Keywords

ionic liquid, microextraction, two phase extraction, 3 phase extraction, ionic liquid stationary phases, thermodynamics and kinetics

Abstract

Ionic liquids are salts that exist entirely as ionic species. They are composed of cation, anion and side chain or linkage group. Due to the different combination of the these groups, the ionic liquid exhibits unique selectivity. Their applications are enormous in the field of analytical chemistry.

The interest of using ionic liquids as gas chromatographic stationary phase has increased in recent years. The low volatility, tailorable physico-chemical property and high thermal stability of ionic liquids make them an ideal choice for gas chromatographic stationary phase. For the present research, commercially available ionic liquid capillary columns were investigate for thermodynamics and kinetics of the retention of alkanes and aromatic hydrocarbons. Van’t Hoff plot was made and the thermodynamic parameters ΔG, ΔH, ΔS were determined. The thermodynamic parameters of SLB-IL 59 and SLB-IL 61 were compared with a conventional polyethylene glycol based stationary phase Stabile Wax -10 having similar Rohrschneider-McReynolds constants. A plot of ΔH, ΔS were made against claimed polarity of the ionic liquid columns. Though the polarity numbers were similar for all the three, the trend in ΔS was different. This shows that Rohrschneider-McReynolds constants by themselves do not predict the actual polarity of these columns and the five probe molecules used for ascertaining the Mc Reynolds constant does not account for all the possible interactions.

The Thermodynamics of retention of aromatic hydrocarbons on ionic liquid stationary phase SLB IL-100 using air as carrier gas was studied. This was compared with the thermodynamic parameters using helium as the carrier gas. A Van Deemter plot was made for SLB-IL 100 using aromatic hydrocarbons as probe analyte and air as career gas. Air when used as carrier gas showed lower optimum value in the Van’ Deemter curve and showed a steeper rise in the slope to the right of the optimum value. The kinetic study revealed the possibility of using ionic liquid stationary phase with air as career gas. The stability of ionic liquid stationary phases in the presence of oxygen in air escalates its commercial usage to new horizon of applications.

Ionic liquid–static headspace single drop micro extraction (IL-SHS SDME) involving three phase equilibrium was performed to extract aromatic hydrocarbons from water. A quick extraction was performed by taking the analyte in a 2 ml vial with o.5 ml headspace volume. Two ionic liquids, 1-Butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl)imide and 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, both having same anion were individually used for the extraction. A direct , no interface introduction of ionic liquid into the gas chromatographic inlet was performed. Ionic liquid stationary phase was used for the chromatographic separation and GC MS for instrumental analysis. The partition coefficient of the aromatic hydrocarbons between the ionic liquid and water were determined by depletion study. The partition coefficient was higher for the aromatic hydrocarbons when 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was used as the extracting micro droplet. The extraction method was then extended for quantitative analysis. The method presented a precision lower than 6.5 % , recovery of 88.9% to 98.1% and the limit of quantitation ranged were 60 pg L-1 for aromatic hydrocarbons. Real samples of drinking water were collected from different source and aromatic hydrocarbons were not detected in any of them.

Ionic liquid–submerged single drop micro extraction (IL-SSDME)involving two phase equilibriam and ionic liquid–static headspace single drop micro extraction (IL-SHS SDME) involving three phase equilibrium were compared in terms of their partition coefficient. Ideally both the extractions were expected to give close values for the partition coefficient . But in actual IL-SHS SDME showed superior extraction when compared to IL-SSDME

Ionic liquid based microextractions not only served as ‘green’ alternative to traditional extraction but also proved to be selective, efficient and time saving sample preparation and pre-concentration technique.

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