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The effect of temperature in chemical separations: 1) reversed-phase liquid chromatography and 2) molecular-receptor interactions

Horner, Anthony (2020) The effect of temperature in chemical separations: 1) reversed-phase liquid chromatography and 2) molecular-receptor interactions. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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In reversed-phase liquid chromatography, temperature significantly affects analyte retention factor. The dependence of analyte retention can be expressed either simply being 1) dependent on temperature alone, or more complex being dependent on 2) mobile phase pH, buffer, and temperature, or 3) mobile phase composition and temperature. Analyte retention commonly increases with decreasing temperature. Temperature assisted solute focusing (TASF) takes advantage of this effect by decreasing the temperature of the head of the column to focus analytes. Temperature is increased to release the concentrated analyte bands, improving method limits of detection. Simple expressions for the temperature dependence of retention allowed capillary scale TASF to be extended to the analytical scale. Understanding more complex dependencies of analyte retention on experimental conditions allows for the optimization of chromatographic separations. We explored the effect of pH and buffer selection on the retention of ionizable analytes when mobile phase pH is near analyte pKa. Buffer ionization enthalpy affects pH change with temperature. Thus, when mobile phase pH is near analyte pKa, buffer selection can be used to modify the temperature dependence of retention. We also compared the ability of mobile phase composition and temperature dependent retention expressions to predict retention for 101 compounds. To extend predictions of the effect of experimental conditions on retention, we explored functional group contributions to thermodynamic parameters. We demonstrated that the temperature dependence of retention, enthalpy, is additive for 39 functional groups, where each functional group’s contribution is temperature and mobile phase composition dependent. Predicted enthalpies show reasonable agreement with literature but demonstrate that different functional groups behave differently on columns with different chemistries and ligand densities. However, functional group contributions accurately predict enthalpy on the same column.
Separately, we studied the complex equilibrium of a molecular receptor extraction. This extraction enhances selectivity by using a fluorous solvent, which is simultaneously hydrophobic and oleophobic, in combination with a fluorous carboxylic acid molecular receptor, which complexes with pyridine. This approach of using a poor solvent in combination with a selective molecular receptor could enhance partitioning of pyridine from aqueous or organic solvent into a fluorous phase.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairWeber,
Committee MemberAmemiya,
Committee MemberMichael,
Committee MemberPawliszyn,
Date: 8 June 2020
Date Type: Publication
Defense Date: 19 February 2020
Approval Date: 8 June 2020
Submission Date: 12 February 2020
Access Restriction: 1 year -- Restrict access to University of Pittsburgh for a period of 1 year.
Number of Pages: 524
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Functional group contributions Liquid chromatography Mobile phase composition dependence Selective separations Solute focusing Temperature dependence
Date Deposited: 08 Jun 2020 16:24
Last Modified: 08 Jun 2021 05:15


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