Anion Exchangers For Ion Chromatography Research Articles

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 poly(glycidylmethacrylate-divinylbenzene)-based anion exchanger for ion chromatography

An anion exchanger has been described by grafting dimethylaminoethyl methacrylate methylchloride (DMC) onto the poly(glycidyl methacrylate-divinylbenzene) (GMA-DVB) subtract. The grafting was performed by coupling of DMC with the pendant double bonds of DVB. Prior to grafting, a hydrolysis treatment to free epoxide groups associated with GMA-DVB substrate enables an improved hydrophilic surface of the obtained anion exchanger. The capacity of the obtained anion exchanger can be manipulated by controlling DMC amount to a great degree. Common seven inorganic anions onto the anion exchanger could be well separated within 20 min and high separation efficiency was obtained, e.g. 46,500/m of the plate count for chloride.

Graphene-coated polymeric anion exchangers for ion chromatography

Carbonaceous stationary phases have gained much attention for their peculiar selectivity and robustness. Herein we report the fabrication and application of a graphene-coated polymeric stationary phase for anion exchange chromatography. The graphene-coated particles were fabricated by a facile evaporation-reduction method. These hydrophilic particles were proven appropriate substrates for grafting of hyperbranched condensation polymers (HBCPs) to make pellicular anion exchangers. The new phase was characterized by zeta potentials, Fourier transform infrared spectroscopy, thermogravimetry and scanning electron microscope. Frontal displacement chromatography showed that the capacities of the anion exchangers were tuned by both graphene amount and HBCPs layer count. The chromatographic performance of graphene-coated anion exchangers was demonstrated with separation of inorganic anions, organic acids, carbohydrates and amino acids. Good reproducibility was obtained by consecutive injections, indicating high chemical stability of the coating.

Covalently-bonded hyperbranched poly(styrene-divinylbenzene)-based anion exchangers for ion chromatography

A number of covalently-bonded hyperbranched poly(styrene-divinylbenzene)-based (PS-DVB) anion exchangers having functional ion exchange layers of different branching degrees are prepared and investigated. The attachment of the hyperbranched functional layers to the substrate surface is realized via anchor secondary amino groups inserted into the polymeric backbone by means of acylation with acetic anhydride followed by reductive amination with methylamine. Further modification of the obtained secondary amino groups is provided by repeating the steps of alkylation with 1,4-butanediol diglycidyl ether (1,4-BDDGE) and amination of the terminal epoxide rings with methylamine (MA). The variation of the number of cycles including modification with 1,4-BDDGE and MA results in selectivity alterations for the obtained anion exchangers. Chromatographic parameters of the obtained stationary phases are evaluated using the model mixtures of anions (F−, HCOO−, Cl−, EtCOO−, BrO3−, NO2−, Br−, NO3−, SO42−, PO43−) with hydroxide and carbonate/bicarbonate eluents. The anion exchangers show the increase of NO2−/EtCOO− and NO2−/BrO3− selectivity and the decrease of EtCOO−/Cl− selectivity with increasing the number of modification cycles. In case of anion exchanger obtained after three modification cycles, the calculated values of column efficiencies for polarizable NO2− and Br− are up to 18,000 and 16,000N/m, respectively.

Hydrothermal carbon nanosphere-based agglomerated anion exchanger for ion chromatography

This work reports the application of hydrothermal carbon nanospheres (HCNSs) as stationary phases in ion chromatography. HCNSs were facilely quaternized through polycondensation of methylamine and 1,4-butanediol diglycidyl ether. The quaternization was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Owing to the electrostatic interaction, quaternized HCNSs were equably attached onto the surface of sulfonated polystyrene-divinylbenzene (PS-DVB) beads to construct the anion exchangers. The aggregation was verified by scanning electron microscopy and elemental analysis. Common anions, aliphatic monocarboxylic acids, polarizable anions, and aromatic acids were well separated on the stationary phases with good stability and symmetry. The prepared column was further applied to detect phosphate content in Cola drink samples. The limit of detection (S/N=3) was 0.09mg/L, and the relative standard deviation (n=10) of retention time was 0.31%. The average recovery was 99.58%.

A novel covalently modified aminated silica-based anion exchanger for ion chromatography

A novel method for the synthesis of anion exchangers for ion chromatography that provides the covalent attachment and spatial movement of the ion-exchange layer away from the silica surface is proposed. The new approach includes the following steps: alkylation of aminated silica with 1,4-butanediol diglycidyl ether and then amination using polyethyleneimine. The obtained anion exchanger allows the simultaneous separation of 11 anions (C2H5COO−, CH3COO−, HCOO−, BrO3−, Cl−,NO2− Br−, NO3− I−, SCN−, ClO4−) in 18 minutes and demonstrates good efficiency (up to 62,000 TP/m for I-) in the single column ion chromatography mode with indirect UV-detection using potassium hydrogen phthalate as an eluent.

Using epichlorohydrin for a simultaneous increase of functional group hydrophilicity and spatial separation from the matrix of anion exchangers for ion chromatography

To increase the efficiency of anion exchangers based on copolymers of styrene and divinylbenzene in ion chromatography a new method for spatial separation and hydrophilization of functional groups using epichlorohydrin is suggested. Synthesis consists of acylation of a matrix by acetic anhydride, reductive amination by methylamine hydrochloride, alkylation of the aminated phase using epichlorohydrin, amination by dimethylamine at the terminal chlorine atom, and quaternization of the terminal amino group with epichlorohydrin. The obtained anion exchangers make it possible to simultaneously determine eight anions (F−, HCOO−, Cl−, NO2− Br−, N3− HPO43− and SO42−) and demonstrate high efficiency (more than 62000 N/m for HPO42−) in a suppressed ion-chromatography mode.

The effect of alkylating agent on the efficiency and selectivity of new polymeric anion exchangers

New anion exchangers for ion chromatography with functional groups of trimethylammonium and 3-chloro-2-hydroxypropyl-N,N-dimethylammonium were obtained. The synthesis included consecutive acetylation of a styrene-divinylbenzene copolymer containing 25% divinylbenzene, reductive amination of carbonyl groups, and subsequent alkylation. Iodomethane and epichlorohydrin were used as alkylating agents. The chromatographic properties of anion exchangers were studied by means of suppressed ion chromatography with conductometric detection. Anion exchangers with the 3-chloro-2-hydroxypropyl-N,N-dimethylammonium group are characterized by better selectivity and higher efficiency for polarizable nitrate and bromide ions, as well as for nonpolarizable chloride, fluoride, nitrite, phosphate, and sulfate ions, compared to those of sorbents with the trimethylammonium group.

A polar-copolymerized method to prepare silica-based anion exchanger for ion chromatography

A novel silica-based strong anion exchanger was developed for ion chromatography by copolymerizing methyltrichlorosilane and 3-chloropropyltrichlorosilane. The method allows the column capacity to be easy control simply by adjusting the ratio of silanes. The unwanted residual silanol groups onto the surface of silica gel could also be greatly reduced by this strategy. The effective column capacity of the column used was measured to be 50.8μequiv/column (2.03μequiv/cm). The exchanger was characterized by solid state CP/MAS 13C NMR and elemental analysis and its separation performance was evaluated for the separation of common inorganic anions. The results showed that the column had good separation efficiency (e.g. the plate number of nitrite is 80,000/m) and the separation mechanism was observed to be dominantly governed by ion exchange mechanism. The utility of the column was demonstrated for the determination of nitrite and nitrate in saliva sample.

Synthesis of polymeric anion exchangers bearing dimethylhydrazine and alkylammonium functional groups and comparison of their chromatographic properties

A new anion exchanger for ion chromatography bearing an N,N-dimethylhydrazine functional group was synthesized by chloromethylation followed by the amination of a copolymer of styrene and divinylbenzene with a crosslinking degree of 50%. Its chromatographic properties were studied in a two-column mode of ion chromatography with conductometric detection. The anion exchanger obtained is characterized by better selectivity and efficiency than ion exchangers bearing alkylammonium functional groups, namely, trimethylamine, triethylamine, N,N,N′,N′-tetramethyldiaminomethane, N,N,N′,N′-tetramethylethylenediamine, and pyridine. Addition of p-hydroxybenzonitrile in the eluant improved the shape of the peak of the nitrate ion and allowed the simultaneous determination of fluoride, chloride, nitrate, phosphate, and sulfate ions.

New High-Performance Techniques for Ion-Exchange Separation

Results of the use of water-soluble cationic polymers for the synthesis of new anion exchangers for ion chromatography, capillary electrophoresis, and electrokinetic chromatography were summarized. The influence of functional groups in polymer molecules on the selectivity of the ion-chromatographic determination of ions and their mobility in capillary electrophoresis was considered.

Polyelectrolyte sorbents for ion chromatography

A method for the synthesis of new anion exchangers for ion chromatography has been proposed. The method is based on the fact that interaction of water-soluble anionic polymers with materials containing negatively charged sulfo groups on the surface gives rise to polyelectrolyte complexes. It is demonstrated that replacement of functional groups in molecules of the polymer affects the selectivity of the ion-chromatographic determination of ions. Recommendations are given for selecting a polymer for the determination of mixtures of inorganic anions and anionic complexes of transition metals in ethylenediaminetetraacetic acid.