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.

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.

Manipulating selectivity of covalently-bonded hyperbranched anion exchangers toward organic acids. Part IV: General algorithm based on the variation of external part of the functional layer.

Novel anion exchangers with mono- and dialkanolamines in the external part of covalently-bonded hyperbranched functional layer were synthesized. Comparison of the chromatographic properties of the prepared stationary phases in suppressed ion chromatography (IC) mode using hydroxide eluent allowed us to evaluate the effect of the number of substituents at nitrogen atom in alkanolamine on selectivity of anion exchangers toward organic acids. Obtained anion exchangers were also examined together with previously described hyperbranched stationary phases with different mono- and diamines in the external part of the layer for evaluating the influence of various parameters on their selectivity. Effects of hydrophilicity, functionality of amine, and the number of substituents at nitrogen atom of amine used in the last modification cycle were established independently from each other, which provided the possibility to tailor selectivity toward organic acids when preparing anion exchanger for solving particular analytical task. Predominance of hydrophilicity as a key factor affecting the separation of weakly retained organic acids over other studied parameters was demonstrated.

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.

The chromatographic properties of three hyperbranched anion exchangers having various diamines in the external part of the functional layer are studied in order to reveal diamine influence on selectivity toward mono- and divalent organic acids. The obtained stationary phases have the same structure of the internal part of the functional layer formed by repeating 4 modification cycles including alkylation with 1,4-butanediol diglycidyl ether (1,4-BDDGE) and amination with methylamine (MA) and differ by the structure of diamine used in the 5th modification cycle. For the first time several diamines (ethylenediamine, (2-aminoethyl)aminoethanol, and N,N'-bis(2-hydroxyethyl)ethylenediamine) are used for completing the last modification cycle in hyperbranching. The performance of three prepared anion exchangers is investigated using KOH and NaHCO3 as eluents and discussed with respect to the differences in hydrophilicity of the external part of the functional layer showing its effect on the separation of organic acids.

Manipulating selectivity of covalently-bonded hyperbranched anion exchangers toward organic acids. Part II: Effect of mono- and dicarboxylic amino acids in the internal part of the functional layer.

Four covalently-bonded hyperbranched anion exchangers based on poly(styrene-divinylbenzene) (PS-DVB) substrate with different structure of the functional layer were prepared using mono- and dianionic amino acids such as glycine, ß-alanine, aspartic acid, and glutamic acid in the internal part of the functional layer. Selectivity of all anion exchangers toward weakly retained organic acids was investigated at different temperatures in order to evaluate the effect of the number of carboxylic groups in the functional layer and its hydrophilicity on the separation. It was found that dianionic amino acids used in the first modification cycle of hyperbranching provide the best resolution for mono- and divalent organic acids, which makes the number of carboxylic groups in the structure of amino acid a key factor in the separation of such analytes with covalently-bonded hyperbranched anion exchangers, while the role of amino acid hydrophilicity is not that significant. Stationary phases prepared using aspartic and glutamic acids provided baseline resolution for quinic, glycolic, acetic, lactic, formic, and galacturonic acids, which are not resolved to baseline with modern commercially available anion exchangers; the increase of temperature was found to be favorable for improving the resolution even further.

Manipulating selectivity of covalently-bonded hyperbranched anion exchangers toward organic acids. Part I: Influence of primary amine substituents in the internal part of the functional layer.

Three covalently-bonded poly(styrene-divinylbenzene)-based (PS-DVB) hyperbranched anion exchangers prepared using primary amines with carboxylic, sulfonic or 2-hydroxyethyl substituents in the internal part of the functional layer were studied and compared for evaluating the effect of amines substituents on the chromatographic performance of the stationary phases. The hyperbranched coating was created on the surface of aminated PS-DVB substrate by repeating the modification cycles including alkylation with 1,4-butanediol diglycidyl ether (1,4-BDDGE) and amination with primary amine; glycine, taurine (2-aminoethanesulfonic acid) or ethanolamine were used in the first cycle, and 4 more cycles were conducted with methylamine (MA). The influence of the structure and type of primary amine used in the first cycle on the retention and selectivity toward inorganic anions, short-chain carboxylic acids, and polyphosphates was investigated using hydroxide eluent. The effect of temperature on the separation of organic acids was also studied for all stationary phases, which revealed the possibility to control and improve resolution for some pairs of analytes.

Anion exchangers with negatively charged functionalities in hyperbranched ion-exchange layers for ion chromatography.

Novel pellicular poly(styrene-divinylbenzene)-based (PS-DVB) anion exchangers with covalently-bonded hyperbranched functional ion-exchange layers containing negatively charged functionalities are obtained and examined. The hyperbranched coating is created on the surface of aminated PS-DVB substrate by repeating the modification cycles including alkylation with 1,4-butanediol diglycidyl ether (1,4-BDDGE), and amination of the terminal epoxide rings with methylamine (MA) or glycine (Gly). The influence of the position and the number of the layers with glycine, as well as of the total number of the layers of amine in the coating on the chromatographic properties of the obtained stationary phases is investigated. Chromatographic performance of the obtained stationary phases is evaluated using the model mixtures of inorganic and organic anions with hydroxide eluent. It is shown that the best selectivity toward weakly retained organic acids and oxyhalides is possessed by the anion exchanger obtained after 5 modification cycles, with glycine being used in the first one. Such anion exchanger packed in 25-cm long column is capable of separating 22 anions in 58min including 7 standard anions, mono-, di- and trivalent organic acids, oxyhalides, and some other double- and triple-charged anions.

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.