Studies On The Retention Mechanism Of Ion Exchange Chromatography

My study on the retention mechanism of ion exchange chromatography includes following parts:1.Because of hydrophobic interaction between the sample ions and the polymer matrix of ion exchanger,it has been shown that a mixed-mode mechanism of ion exchange and adsorption interaction occurs in ion exchange chromatography.In consideration of the difference of exchange capacity and adsorption area,an equation for interrelation among retention values of the columns was derived as follows:V'_R(X)/V'_R(S2)=a·V'_R(S1)/V'_R(S2)+b,where a and b are expressed by distribution coefficient and adsorption coefficient of predicted ion(x),benzoic acid or o-phthalic acid(S1)and toluene(S2).The calculations of fifteen anions (fluoride,chloride,nitrate,sulfate,phosphate,dihydroxybutyric acid,pyruvic acid,acetic acid,acrylic acid,salicylate,benzoic acid,malonic acid,tartaric acid, oxalic acid and o-phthalic acid)on five Dionex IonPac AS9-HC columns in accordance with the developed method have shown the good precision of the above equation.The correlation coefficients calculated for monovalent anions were between 0.9～0.999 and for divalent were between 0.999 and 1.This work can offer a new method for studies on adsorption interaction of ion exchanger.2.The effect of oven temperature(293,303,313,318,323K)on separation parameters of a chromatographic system of IonPacAS9-HC column and 9 mmol/L Na₂CO₃(containing 50%acenitrile)was studied.Thermodynamic constantsâ–³H andâ–³S' were calculated.Based on these values,the retention mechanism of solute ions with different structure was discussed and the relationships between thermodynamic functions and molecular structures were evaluated.21 structure parameters that were calculated by HF/6-31^* level were chosen based on the hypothesis that there were three kinds of intermolecular force including electrostatic interaction,hydrogen bond force and dispersion force in the process of ion-exchange chromatography.The models of quantitative structurethermodynamic constants relationship,which were established through stepwise regression techniques,were used to interpret the chromatographic retention mechanism.3.According to the structural properties of 25 carboxylic acids that were fully computed at HF/6-31^* level in the above chapter,several structure-retention relationships(QSRR)under the different oven temperatures by using the method of multiple linear regression have been developed.Comparing these models,the main factors affecting the retention time of carboxylic acid were investigated.As a result,the chromatographic retention mechanism was discussed.