Mixed-mode liquid chromatography of carboxylic acids and inorganic anions on a latex-based pellicular stationary phase

The retention behaviour of mono-, dicarboxylate and inorganic anions on latex-based pellicular anion-exchanger was investigated. This paper is focused on the possible retention mechanism providing a retention database on a variety of mobile phase compositions. It has been demonstrated that anions can interact with the cation-exchange layer on the highly crosslinked latex-based pellicular phase as well as with the anion-exchange sites. A hypothesis is proposed to explain a mixed-mode retention of the series of analytes. A combination of two mechanisms has been found responsible for the enhanced selectivity: ion-exchange and ion-exclusion. Applications include the separation of formate, acetate, propionate, lactate, pyruvate, oxalate, malonate, succinate, tartrate, fumarate, maleate, chloride, nitrate and sulphate with NaOH eluent using suppressed conductivity detection. The study effectively characterizes the behaviour of different analytes under elution conditions of practical importance.