Synthesis and characterization of triple acid stationary phases for cation exchange chromatography using click chemistry and atom transfer radical polymerization

Triple acid cation exchangers were synthesized by a combination of atom transfer radical polymerization (ATRP) and alkyne azide click chemistry. Oxidized uniform PS/DVB particles were functionalized stepwise with carboxylic, phosphonic and sulfonic acid groups to prepare stationary phases with unique selectivity. The amount of sulfonic acid groups was varied while the amount of carboxylic and phosphonic acid groups remained constant, resulting in a set of stationary phases for trend analysis. The presence of sulfonic acid groups gives a good selectivity for the monovalent standard cations, while stationary phases without sulfonic acid groups show a coelution of monovalent ions. Furthermore, the presence of sulfonic acid groups results in a retention gap between mono and divalent ions, which can be used to separate target analytes inside the gap between these mono and divalent matrix ions. The relevant inorganic matrix cations Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ were separated together with mono-, di-, trimethylamine and tetramethylammonium in 45 min using a nitric acid gradient elution and suppressed conductivity detection. The retention gap between the monovalent and divalent ions was used to elute the analytes together with these ubiquitous matrix ions.