| Ionic liquids(ILs)are molten organic salts whose melting point are around room temperature.They are composed of asymmetrical organic cations and inorganic anions.Because of the unique molecular structure,ionic liquids exhibit many significant advantages over traditional organic solvents,including negligible vapor pressures at room temperature,wide liquid phase temperature ranges,good thermal stabilities,high viscosities,strong dissolving abilities,and so on.It is because of these properties that ionic liquids have been the promising gas chromatography stationary phases.Ionic liquid bonded polysiloxane(PIL)stationary phases not only inherit the character of“dual nature”from ionic liquids,but also inherit the excellent stability and film-forming ability from polysiloxanes.However,the species and amount of the reported ionic liquid bonded polysiloxane stationary phases are still limited to date and the systematic research on them is basically a virgin ground.Quantitative structure-retention relationship research(QSRR)is an important chromatographic technique for relating the variations in retention time to the changes of structure parameters.The constructed QSRR models not only can predict the chromatographic retention data of the untested solutes,but also can explain the retention mechanisms partly.All these would help to design or select perfect stationary phases.But until now,QSRR hasn’t been applied to the field of IL stationary phases.In this paper,a novel synthesis strategy of PILs was proposed.Upon this approach,I synthesized sixteen PILs differing in IL content,IL group or combination of different IL groups.Then the effects of different IL structures on interaction characteristics and separation selectivity performances were respectively studied by means of solvation parameter model and separating a series of typical mixtures.At last,the QSRR models were constructed using SPSS and SIMCA-P statistical programs for the retention values of benzene derivative compounds on different PILs with predictive and explanatory purposes.The main contents are as follows:1.IntroductionCapillary column gas chromatography was introduced briefly in aspects of the related information and research survey of the stationary phases,and the column preparing process,and the classifying methods of stationary phases and the research survey of ionic liquids stationary phases were described emphatically.On the other hand,the basic steps for constructing QSRR models were introduced briefly,and the variable selection methods and model construction methods were described emphatically.Lastly,the purpose of this dissertation was proposed.2.Synthesis and performance evaluations of ionic liquid bonded polysiloxane stationary phases based on a flexible and convenient strategyA novel synthesis strategy for ionic liquid bonded polysiloxanes was proposed.The polysiloxane with imidazole groups at the side chains was synthesized firstly,and then these imidazole groups further reacted with halogenated compounds to produce various IL groups.Upon this approach,sixteen PIL stationary phases differing in IL content,IL group or combination of different IL groups were synthesized and used to prepare capillary columns through static coating method,respectively.Then the column efficiency,durability and polarity of these columns were evaluated.It was resulted that most columns had column efficiency values over 3000 plates/m,and these columns had quite different general polarity indexes(GPIs)falling in a broad range from 218 to 717.In addition,IL content,structure of the IL and combination of different IL groups had noticeable influences on the GPIs and interaction features of the stationary phases.After that,the separation performances of these PIL stationary phases were demonstrated by separating various mixed samples of aliphatic esters,dichloro-anilines,alcohols,aromatic amines,substituted alkanes,and so on.The results indicated that there were significant differences in the separation selectivity not only between PILs and conventional polar stationary phases,but also among different PILs.3.Interaction parameter tests of PIL columnsThe solvation parameter model was introduced detailedly in aspect of the steps of constructing the model and the definitions of all parameters.Then the interaction characteristics of these sixteen PILs were measured through the solvation parameter model.It was resulted that the stability of the solvation parameter models for these PILs is high.Different PILs owned different interaction characteristics,and b of these PILs fell in a much broader range(from-0.316 to 4.691 at 100 ~oC)than that of the ionic liquids reported.On the basis of this result,it is hopeful to exploit new ionic liquid columns with strong hydrogen bond acidity.4.Hydrogen bond acidity of PIL and its effect on the separation performanceTwelve Mono-PIL columns were used to explore the structural factors influencing the strength of hydrogen bond acidity by deeply analyzing the data of solvation parameter model.It was resulted that the changes in the strength of hydrogen bond acidity brought about by the IL content were very different depending on the structure of the substituent group.When the substituent groups were dodecyl groups,decreasing the IL content could effectively strengthen the hydrogen bond acidity,but weaken the hydrogen bond acidity when the substituent groups were tetraglycols.In addition,when the IL content was the same and the substituent groups were linear alkyls,shortening the alkyl chain would obviously strengthen the hydrogen bond acidity.But if the alkyl chain was branched,the strength of the hydrogen bond acidity would be inconsistent with the rule obtained by the PILs whose substituent groups were linear alkyls.For the PILs whose substituent groups were polar functional groups and the IL content was the same,increasing the electron-rich functional groups would weaken the hydrogen bond acidity,instead.Moreover,the ultimate reason for the obvious changes in hydrogen bond acidity was the destruction of hydrogen-bonded network.On the other hand,a series of compounds(eg.aromatic isomers,dichloroanilines,substituted alkanes,alcohols,esters,etc.)were separated on these PIL columns to explore the influences of the hydrogen bond acidity of PIL on the separation performances.It was resulted that the elution orders of some dichloroanilines,aliphatic esters and alcohols would change with the change of the hydrogen bond acidity.And increasing the hydrogen bond acidity could improve the separation selectivity for the aromatic isomers,substituted alkanes and alcohols.5.Effect of PIL structures on interaction forces except for hydrogen bond acidity and on the separation selectivityTwelve Mono-PIL columns were used to explore the structural factors influencing the strength of interaction factors except for hydrogen bond acidity by deeply analyzing the data of solvation parameter model.It was resulted that the change rule of these interactions with the IL content was the same even if the substituent groups were different.With the decrease of the IL content,l increased and the other interactions decreased.When the IL content was the same and the substituent group was alkyl group,these interactions of different stationary phases had no distinct difference except for PIL-C8(16%).And for the PILs whose substituent groups were polar functional groups and the IL content was the same,e,s and a all increased with the increase of the amount of electron-rich functional groups and the increase of electron density of the functional groups,and the change in l was exactly the opposite.On the other hand,a series of compounds(like aromatic isomers,aliphatic esters,dichloroanilines,phthalic acid esters,aromatic amines,substituted alkanes,alcohols,etc.)were separated on these PIL columns to explore the influences on the separation performances caused by the change in these interactions.It was resulted that the primary interactions influencing the separation performances of different compounds were very different.For example,s,a and b had a serious effect on the separation of aromatic isomers;s,b and l had a strong effect on the separation of aliphatic esters;b and a had a significant effect on the separation of dichloroanilines,and so on.These results would be of great benefit to the rational design or selection of a stationary phase for a certain analyte.6.Effect of combining different IL groups on the stationary phase performancesFour Bi-PIL stationary phases and three corresponding Mono-PIL stationary phases were used to explore the effect of combination of different IL groups on the interaction characteristics.It was resulted that before and after combining different IL groups,the changes in l and e were fairly minor,and the changes in b was very remarkable.On the other hand,a series of compounds(like aromatic isomers,aromatic amines,alcohols,phthalic acid esters,substituted alkanes,aliphatic esters,etc.)were separated on these PIL columns to explore the effect of combining different IL groups on the separation performances.It was resulted that after combining IL groups,Bi-PILs displayed greatly improved separation performances for aromatic amines and alcohols,and the separation performances for phthalic acid esters,substituted alkanes and aliphatic esters were also better than some Mono-PILs.7.Quantitative structure-retention relationship study of benzene derivative compounds on the Mono-PIL stationary phasesFirstly,five coefficients of the solvation parameter model were used as variables in the cluster analysis model and nine Mono-PIL stationary phases were divided into three categories:hydrogen bond acidic columns,hydrogen bond basic columns and the others.Then 48 benzene derivative compounds were used as the probes,their Kovats retention indexes on the nine Mono-PIL stationary phases were used as dependent variables,and their structural parameters were used as independent variables to construct different linear QSRR models.It was resulted that the major structural factors that affected the retention behaviors of the probes on Mono-PIL stationary phases were boiling point,dipole moment,octanol-water partition coefficient,and so on.And for different Mono-PILs,the effect intension of different structural factors was also different.For these three QSRR models which had only one dependent variable,MLR and MLR-PLS models owned better stability and predictability than PLS-PLS,MLR-PLS and PLS-PLS could provide more useful information because PLS method combined the merits of principal component analysis,canonical correlation analysis and regression analysis,and the independent variables obtained by PLS-PLS were the fewest and the easiest to be interpreted.In the practical work,we can choose different models according different need.Additions,multi-dependent variable PLS model was also constructed to study the relationships of different Mono-PIL stationary phases and the structural factors influencing the retention of samples on different Mono-PIL stationary phases.The results were consistent with that of the other QSRR methods.In conclusion,constructing QSRR models not only can classify PIL stationary phases,but also can contribute to select stationary phases pertinently through predicting the retention indexes of benzene derivative compounds.8.Quantitative structure-retention relationship study of benzene derivative compounds on the Bi-PIL stationary phasesFirstly,five coefficients of the solvation parameter model were used as variables in the cluster analysis model to classify the Bi-PILs and the corresponding Mono-PILs.The result displayed that the interaction characteristics of PIL-C8&PP1 and PIL-C8&PP2 were alike and they were both similar to that of PIL-PP(16%)column.The interaction characteristics of PIL-CN&PP were similar to that of PIL-CN(16%)column.Then 48 benzene derivative compounds were used as samples,their Kovats retention indexes on the bifunctional stationary phases and the corresponding monofunctional stationary phases were used as dependent variables,and their structural parameters were used as independent variables to construct different linear QSRR models.It was resulted that all of the test parameters were very large,and the stability and predictability of these models were very good.MLR and MLR-PLS models displayed that PIL-C8&PP2 and PIL-CN&PP were alike in separation performances and this conclusion was the same with that of multi-dependent variable PLS model.PLS-PLS model shown that PIL-C8&PP1,PIL-C8&PP2 and PIL-CN&PP were all alike in separation performances,which all affected greatly by the 3-phenylpropyl group.In conclusion,constructing QSRR models could study the relationships of PIL stationary phases before and after combining IL groups preliminarily. |
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