Abstract:

A polymer-based strong anion stationary phase modified by quaternary ammoniated allyl glycidyl ether (AGE) for ion chromatography (IC) was developed. It was prepared by surface copolymerization between AGE and the pedant double bonds associated with hydrolyzed poly(glycidylmethacrylate-divinylbenzene) (GMA-DVB) substrate, followed by quaternization with N,N-methyldiethanolamine (a tertiary amine, MDEA). The synthesis conditions were optimized, including the type of organic tertiary amines (MDEA, N,N-dimethylethanolamine, trimethylamine), substrate hydrolysis, the amount of monomer and initiator, reaction temperature and reaction time. The obtained anion stationary phase was characterized by scanning electron microscope and elemental analysis. MDEA was observed to be the best quaternization reagent since the anion exchanger obtained by such reagent showed good separation and suitable retention time towards model inorganic anions. The resulting reason probably lies in higher hydrophilicity of MDEA relative the other two ones. The use of rich epoxy groups of GMA-DVB to introduce the functional groups was commonly used in many previous reports. Here the epoxy groups were firstly hydrolyzed to be diol groups and the pendant double bonds onto the surface of GMA-DVB particles were used to graft AGE. The data achieved indicated that the use of hydrolyzed GMA-DVB substrate would be helpful to reduce anion exchange capacity and unwanted non-ion exchange interaction, in which the rich epoxy groups were converted to hydroxy groups. More important, the obtained anion exchanger after hydrolytic treatment could offer a significantly reduction of retention time (~68%) and a ~1.67-fold higher plate count (take Br^- as an example). The apparent capacity of the phase was computed to be 264 μmol/g by content of N data and its effective capacity was measured to be 98.5 μmol/column by the breakthrough curve method. Under the optimal chromatographic conditions, the obtained stationary phase showed baseline separation of seven common inorganic anions in less than 13 min using carbonate-bicarbonate mixed eluent, exhibiting high separation efficiency and peak shape, e. g. 49000 plate/m and 38000 plate/m of the theoretical plate counts respectively for chloride and nitrate, and their asymmetric factor were 1.3 and 1.4. These can be comparable or slightly higher than those of commercial columns. The fitted equation of the eluent concentration and the retention factors of model anions was proved that ion exchange model dominates the retention mechanism of the anion stationary phase. This offers a simple way to prepare anion exchanger and to manipulate anion exchange capacity. The utility of the obtained anion exchanger has been demonstrated to the analysis of tap water.

Key words: ion chromatography (IC), poly(glycidylmethacrylate-divinylbenzene) (GMA-DVB), pedant double bonds, stationary phase