Manipulating selectivity of covalently-bonded hyperbranched anion exchangers toward organic acids. Part III: Effect of diamine structure in the external part of the functional layer

A hyperbranched anion exchanger obtained by carboxylate surface modified polymer substrate for ion chromatography

A surface-carboxylated polymer substrate-based hyperbranched anion exchanger has been described for ion chromatography (IC). It is prepared by grafting maleic anhydride onto porous polystyrene-divinylbenzene (PS-DVB) microspheres, then hydrolyzed to generate carboxylate groups being anchor points for electrostatic attachment of positively hyperbranched polymer obtained by cyclic reaction of diepoxides and amines. The obtained anion exchanger shows high hydrophilicity and good chromatographic performance, as demonstrated by the separation of common inorganic anions, including polarizable anions, disinfection byproducts and organic acids. High efficiency and good peak shape were achieved, as indicated by the theoretical plate counts of 45,000/m, 51,000/m and asymmetry factors of 1.12, 1.08 for nitrite and bromide, respectively. A desirable feature of such carboxylated groups-based anion exchanger is elimination of possible bleed of sulfate encountered in common sulfonated-based ones, avoiding sulfate blank in the case of the analysis of trace anions in pure water.

Hybrid grafted and hyperbranched anion exchangers for ion chromatography

Novel grafted anion exchangers with covalently bonded hyperbranched functional layers were prepared and evaluated for the separation of monovalent standard inorganic anions and oxyhalides. Preparation of base coating included grafting highly polar N-vinylformamide to the ethylvinylbenzene-divinylbenzene (EVB-DVB) substrate surface in highly polar solvent (methanol) with subsequent hydrolysis of grafted amide polymer in basic media, which resulted in preparation of polymer chains with multiple primary amino groups. Those amino groups were used as attachment points for forming hyperbranched anion-exchange layers using 1,4-butanediol diglycidyl ether and primary mono- or diamine (methylamine or 1,3-diaminopropane, respectively). The effects of hyperbranching reaction cycles number on selectivity were evaluated which revealed that selectivity and capacity can be controlled independently for the covalently bonded stationary phases in contrast to electrostatically bonded phases. It was demonstrated that unlike for electrostatically bonded phases, the intentional increase of crosslink by using primary diamine instead of primary monoamine doesn't cause the shift of selectivity coefficients. It was also shown that crosslink distribution throughout the hyperbranched layer is an important factor determining selectivity of hyperbranched anion exchangers.

A review of the design of packing materials for ion chromatography

The development of ion chromatography has made remarkable progress in the past few decades, and it is now widely used for the analysis of common ions and organic compounds. Ion chromatography has many advantages, such as fast, high sensitivity, good selectivity and support for simultaneous analysis of multiple ionic compounds. In order to meet the high requirements of material analysis, new packing materials for ion chromatography with higher sensitivity and selectivity have been developed. In this paper, a lot of knowledge of ion chromatography is reviewed, and the development of ion chromatographic packings in recent years, especially in the last five years, is summarized.

Prospects of using hyperbranched stationary phase based on poly(styrene-divinylbenzene) in mixed-mode chromatography

Evaluation of the chromatographic properties of covalently bonded hyperbranched stationary phase based on poly(styrene-divinylbenzene) (PS-DVB) and containing zwitterionic fragments in the structure of functional layer was conducted in suppressed ion chromatography (IC), reversed phase high performance liquid chromatography (RP HPLC), and hydrophilic interaction liquid chromatography (HILIC) modes. Besides the possibility of resolving 20 inorganic anions and organic acids using KOH eluent in suppressed IC, prepared resin provided the separation of alkylbenzenes in RP HPLC, water-soluble vitamins, amino acids, and sugars in HILIC mode. Trends in the retention of hydrophobic and polar analytes on the prepared stationary phase indicated the dominating effect of analyte nature on the retention mechanism and proved satisfactory hydrophilization of PS-DVB surface with hyperbranched functional layer for retaining polar compounds. The obtained results revealed good prospects of using hydrophobic PS-DVB substrate for preparing stationary phases for mixed-mode chromatography.