Novel polymer-based anion-exchangers with covalently-bonded functional layers of quaternized polyethyleneimine for ion chromatography.

For the first time novel pellicular anion-exchangers with functional layers of quaternized branched polyethyleneimine (PEI) covalently bonded to the surface of aminated poly(styrene-divinylbenzene) (PS-DVB) with 1,4-butanediol diglycidyl ether (1,4-BDDGE) as a linker are obtained and studied. The proposed method of synthesis includes alkylation of PS-DVB substrate containing secondary aminogroups with 1,4-BDDGE followed by amination with branched PEI containing primary, secondary, and tertiary amino groups. Quaternization of amino groups of PEI required for increasing ion-exchange capacity of the stationary phase is provided with two epoxides - glycidol and 1,4-BDDGE, which results in the considerable variations of ion-exchange selectivity. Chromatographic properties of the obtained anion-exchangers are evaluated using various model mixtures of anions (F-, HCOO-, CH3COO-, C2H5COO-, Cl-, BrO3-, NO2-, Br-, NO3-, ClO3-, S2O32-, C2O42-, CrO42-, SO42-, PO43-, I-, SCN-) in hydroxide and carbonate/bicarbonte eluents. All anion-exchangers show better selectivity toward the anions of weakly retained organic acids (acetate, formate, propionate) as compared with previously reported chemically derivatized anion-exchangers with monomeric functional sites in the ion-exchange layer. In terms of separation abilities, novel anion-exchangers with covalently-bonded PEI are not inferior to some commercial columns with grafted polymeric anion-exchange layer. Anion-exchanger quaternized with more hydrophilic glycidol packed in 10-cm long column enables the separation of 16 anions including weakly retained and highly retained polarizable ones within 26 min using gradient elution. Column efficiencies for both anion-exchangers with quaternized PEI are up to 32000 N/m and 37000 N/m in case of hydroxide and carbonate eluent, respectively, which is comparable with the values demonstrated by commercially available columns of related chemistry.