Mixed-mode retention mechanism of ion exchange chromatography

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. Experimental retention data were obtained on five Dionex IonPac AS9-HC columns using a 9 mmol/L Na2CO3 solution containing 50% (V/V) acetonitrile as eluent. The calculations of twelve anions (fluoride, chloride, sulfate, phosphate, dihydroxybutyric acid, pyruvic acid, acetic acid, acrylic acid, benzoic acid, malonic acid, tartaric 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 and 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.