Evaluating The Solvation Properties Of Ionic Liquids With Varied Cation/anion Composition Based On The Solvation Parameter Model

Ionic liquids,collectively known as organic salts,are non-molecular ionic solvents with melting points at or below 100?.In most cases,ionic liquids are composed of nitrogen-or phosphorus-containing organic cations with inorganic anions or organic anions.Due to the electrostatic interactions associated with the cation and anion moieties comprised in the ionic liquids,as well as their ability to undergo various intermolecular interactions with one another,ionic liquids exhibit beneficial characteristics,such as high chemical stability,wide liquid range,negligible vapor pressure,and relatively high viscosity.These characteristics and solvation properties can also be finely tuned to meet specific requirements by imparting different functional groups and/or altering the combinations of cations and anions in the ionic liquids.In this study,the Abraham solvation parameter model is used via gas chromatography to characterize the solvation properties of several ionic liquids with varied cation/anion composition and binary mixtures of two different ionic liquids.In addition,ionic liquids based on natural amino acids were synthesized and used as stationary phases for gas chromatographic separation.Meanwhile,the solvation properties of amino acid ionic liquids were evaluated.A fundamental understanding into the solvation characteristics of these unique solvents will provide additional insight in choosing the ionic liquids capable of exhibiting desired solvation properties for specific applications.This dissertation includes five chapters:In Chapter 1,the structure and classification of ionic liquids were introduced and the relationship between the physicochemical properties of ionic liquids and their structures?i.e.,cation and anion combinations?,and how these aspects influence their applicability as stationary phases in gas chromatography were discussed.Subsequently,significant advances pertaining to the applications of ionic liquids in microextraction,liquid and gas chromatography,capillary electrophoresis,mass spectrometry,and electrochemical sensing were presented.The general retention parameters related with gas chromatography columns as well as common models used to illustrate the retention mechanisms and characterize various solvation interactions were described.In Chapter 2,five magnetic ionic liquids,namely 1-buty3-methylimidazolium tetrachloroferrate?[BMIM][FeCl₄]?,1-benzy3-methylimidazolium tetrachloroferrate?[BnMIM][FeCl₄]?,1,3-dibenzylimidazolium tetrachloroferrate?[BnBnIM][FeCl₄]?,1-menaphthy3-benzylimidazoliumtetrachloroferrate?[NBnIM][FeCl4]?,and trihexyl?tetradecyl?phosphonium tetrachloroferrate([P_6,6,6,14][FeCl₄])were coated onto the inner walls of fused-silica capillary columns and used as gas chromatography stationary phases for the first time.Then the Abraham solvation parameter model was used to characterize the solvation interactions of magnetic ionic liquids.The role of the functional groups,nature of the cation,and anion type on the system constants were evaluated.The presence of benzyl group affected the dipolarity/polarizability of magnetic ionic liquids,while the change of cation type yielded modest influence on the dipolarity/polarizability.The hydrogen bond basicity was determined by the anion and could be modulated by the cation.The chromatographic performance of the magnetic ionic liquids stationary phases was evaluated by examining the retention behavior and separation selectivity for chosen analytes.The modification of ionic liquids structure resulted in a significant effect on the retention behavior as well as separation selectivity for many solutes,including reversed elution orders of some analytes.The results can be used as a guide for choosing FeCl₄-based magnetic ionic liquids capable of exhibiting desired solvation properties while retaining important physical properties including paramagnetic nature and high thermal stability.In Chapter 3,six neat ionic liquids,namely 1-buty3-methylimidazolium bis[?trifluoromethyl?sulfonyl]imide?[BMIM][NTf2]?,1-buty3-methylimidazolium dimethylphosphate?[BMIM][Me₂PO₄]?,1-buty3-methylimidazolium trifluoromethanesulfonate?[BMIM][TfO]?,1-buty3-methylimidazolium methylsulfate?[BMIM][MeSO₄]?,8-methy1,8-diazabicyclo?5.4.0?undec-7-enemethylsulfate?[Me-DBU][MeSO₄]?,1-buty1-methylpyrrolidinium bis[?trifluoromethyl?sulfonyl]imide?[BMPyrr][NTf₂]?,and five binary mixtures of two different ionic liquids were coated onto the inner walls of capillary columns.A total of eleven neat or binary ionic liquids stationary phases were characterized using the Abraham solvation parameter model to investigate the effects of the cation,anion and ionic liquid composition on the system constants of the resulting stationary phases.Results revealed that tuning the composition of the stationary phase allowed for fine control of the retention factors and separation selectivity for alcohols and ketones as well as selected aromatic compounds.A reversal of elution order was observed for particular classes of analytes when the composition of binary ionic liquids was changed.This study provides one of the most comprehensive examinations up-to-date on the relation between neat ionic liquid structure or composition of binary ionic liquids and the resulting solvation characteristics and gives tremendous insight into choosing suitable ionic liquids as gas chromatography stationary phases for solute specific separations.In Chapter 4,chromatographic retention factors were measured for 45 different organic solutes of varying polarity and hydrogen-bonding capability on an anhydrous1-?2-methoxyethyl?-1-methylpyrrolidiniumtris?pentafluoroethyl?trifluorophosphate,?[MeoeMPyrr][FAP]?,stationary phase at both 50?and 80?.The experimental retention factor data were combined with recently published thermodynamic data for solutes dissolved in?[MeoeMPyrr][FAP]?to give the corresponding gas-to-liquid partition coefficients?logK?at both 25?and 50?.The water-to-anhydrous?[MeoeMPyrr][FAP]?partition coefficients?logP?at 25?were also calculated using published gas-to-water partition coefficient data for the solutes studied.The derived partition coefficients were analyzed in accordance with the Abraham model.The system constants are attained through multiple linear regression analysis of the logK term,logP term and the solute descriptors.All regression analyses were performed using R-Project software based on R script program.And the equation coefficients for the[MeoeMPyrr]⁺cation were obtained.The derived Abraham model correlations were statistically quite good and back-calculate the observed 105 logK and 102 logP values to within a standard deviation of 0.14 and 0.16 log units,respectively.The water-to-anhydrous?[MeoeMPyrr][FAP]?partition coefficients?logP?for various solutes and the equation coefficients for the[MeoeMPyrr]⁺cation were calculated for the first time.In Chapter 5,six amino acid ionic liquids,namely leucine ethyl ester tetrafluoroborate?[Leu-OEt][BF4]?,leucine ethyl ester hexafluorophosphate?[Leu-OEt][PF6]?,leucine ethyl ester bis[?trifluoromethyl?sulfonyl]imide?[Leu-OEt][NTf₂]?,phenylalanine ethyl ester tetrafluoroborate?[Phe-OEt][BF₄]?,phenylalanine ethyl ester hexafluorophosphate?[Phe-OEt][PF₆]?,phenylalanine ethyl ester bis[?trifluoromethyl?sulfonyl]imide?[Phe-OEt][NTf₂]?were synthesized and used as stationary phases in gas chromatography.Meanwhile,Abraham solvation parameter model were used to evaluate the solvation characteristics.The system constants indicated that the dipolarity/polarizability and the hydrogen-bond interaction play a major role among five molecular interactions between stationary phases and solute molecules.A fundamental understanding into the solvation characteristics of these amino acid ionic liquids can be used as a guide to choosing the appropriate amino acid ionic liquids for specific applications in various fields.The chromatographic separation performance was evaluated by a Grob test mixture,n-alkanes,alcohols,esters and aromatic isomers.The present results demonstrate that these amino acid ionic liquids stationary phases possess excellent chromatographic separation performance,and may be applicable as gas chromatography stationary phases for more application.