Access Type

Open Access Dissertation

Date of Award

January 2012

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Colin F. Poole

Abstract

ABSTRACT

DETERMINATION OF DESCRIPTORS BY LIQUID-LIQUID PARTITION AND CHROMATOGRAPHIC METHODS

by

THUSHARA KARUNASEKARA

September 2012

Advisor: Prof. Colin F. Poole

Major: Chemistry (Analytical)

Degree: Doctor of Philosophy

Partition coefficients for varied compounds were determined for several totally organic biphasic systems using formamide, propylene carbonate, ethylene glycol or dimethyl sulfoxide as the base solvent and n-heptane, 1,2-dichloroethane, 1-octanol or isopentyl ether as the counter solvent. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of these systems with other totally organic and water-based partition systems. These totally organic biphasic solvent systems offer a complementary approach to water-based partition systems for sample preparation and the determination of descriptors for compounds virtually insoluble in water or unstable in water.

A new method of solvent classification is proposed based on the five system constants of the solvation parameter model for transfer of neutral compounds from the gas phase to solvent and hierarchical cluster analysis for identifying solvents with similar properties and for organizing them into selectivity groups. This method resulted in the classification of 36 common solvents used in chromatography into seven selectivity groups with four solvents (2,2,2-trifluoroethanol, N,N-dimethylformaide, dimethyl sulfoxide and water) behaving independently. The classification scheme provides a logical approach for solvent selection as the first step in chromatographic method development. A similar approach for the transfer of neutral compounds between condensed phases and hierarchical cluster analysis was used to classify 19 aqueous and 17 totally organic biphasic partition systems for liquid-liquid extraction. The totally organic biphasic partition systems exhibit an almost continuous range of properties with minimal group formation demonstrating a wider and complementary range of selectivity to the aqueous biphasic systems. The classification of the liquid-liquid partition systems provides a suitable method of identifying suitable systems for sample preparation based on liquid-liquid extraction and for the simulation of extractions for target compound isolation.

Retention factors on a minimum of eight stationary phases at various temperatures by gas-liquid chromatography and liquid-liquid partition coefficients for eight totally organic biphasic systems were combined to estimate descriptors for 28 fragrance compounds with an emphasis on compounds that are known or potential allergens. Similar aproch with additional liquid chromatographic measurements was used to estimate descriptors for 24 esters widely used as plasticizers and solvents in industry. The descriptors facilitated the estimation of several properties of biological and environmental interest (sensory irritation threshold, odor detection threshold, nasal pungency threshold, skin permeability from water, skin-water partition coefficients, octanol-water partition coefficients, absorption by air particles, adsorption by diesel soot particles, air-water partition coefficients, and adsorption by film water).

A combination of gas chromatography and liquid-liquid partition in totally organic biphasic systems is used to determine descriptor values for compounds of low volatility suitable for characterizing open tubular columns at high temperatures. The descriptor database of varied compounds includes several difficult to determine by conventional techniques due to their low water solubility or stability. The descriptor database facilitates an expansion of the descriptor space and compound variation for characterizing separation systems. As an application the descriptor database is used to determine the system constants for SPB-Octyl, HP-5, Rxi-5Sil MS, Rtx-440, and Rtx-OPP for the temperature range 200-300,,aC. As an example of the broader affect of temperature on column selectivity the variation of the system constants for Rtx-440 over the temperature range 60-300,,aC is described in detail. These studies demonstrate the persistence of polar interactions to the highest temperature studied and that at high temperatures selectivity differences persist for moderately polar stationary phases.

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