Key Takeaways & Executive Findings
- •• • Organic polymer matrices, particularly PS-DVB and EVB-DVB, offer pH tolerance from 0 to 14, enabling the use of hydroxide eluents for suppressed IC, which is critical for analyzing weakly dissociated anions like bromate at trace levels (e.g., regulatory limits in drinking water). • • Silica-based stationary phases are limited to pH 2–8, restricting their use with common IC eluents; this narrow pH range precludes their application in suppressed IC, which typically requires high-pH eluents, thus favoring polymer matrices for environmental anion analysis. • • Functionalization strategies, such as grafting quaternary ammonium groups with hydrophilic spacers, have been shown to improve separation efficiency and selectivity; for instance, anion exchangers with dihydroxy-containing alkyl substitutes in quaternary ammonium groups exhibit enhanced hydrophilicity and chromatographic performance. • • The review highlights the need for high-capacity anion exchangers to achieve low detection limits; for example, experimental design optimization of elution systems for high-capacity anion chromatography with suppressed conductivity detection has been applied to improve sensitivity for trace anions in complex matrices.
Abstract
Ion chromatography (IC) is the core analytical method for qualitative and quantitative determination of anions in complex water environments, and its separation efficiency highly depends on the performance of the stationary phase. This review systematically summarizes recent progress in the preparation and functionalization of IC stationary phases, addressing the urgent need for high selectivity and sensitivity in water anion analysis. The characteristics of organic polymer-based and inorganic-based matrices are compared, highlighting the advantages of polymer matrices such as poly(methacrylate), poly(vinyl alcohol), polystyrene-divinylbenzene (PS-DVB), and ethylvinylbenzene-divinylbenzene (EVB-DVB) in terms of wide pH tolerance (e.g., pH 0–14 for PS-DVB) and organic solvent compatibility, which allow the use of strong acid or base eluents. Various functionalization strategies are discussed, including the introduction of quaternary ammonium groups, hydrophilic modifications, and grafting of functional layers, which enhance separation selectivity and detection capability. The review also covers the development of hybrid stationary phases and the application of IC in monitoring trace pollutants in water, such as bromate, chlorite, chlorate, fluoride, and nitrate, as regulated by Chinese standards (GB 5749—2022). Future trends are projected, focusing on novel materials for precise identification and high-throughput monitoring. The paper provides a comprehensive reference for the design of high-performance stationary phases, emphasizing the importance of matrix selection and surface chemistry in achieving robust and sensitive anion analysis.
1. Introduction
Ion chromatography (IC) is indispensable for the determination of anions in water, yet its performance is governed by the stationary phase. Commercial silica-based columns suffer from a narrow pH tolerance (2–8), which precludes their use with the high-pH eluents required for suppressed conductivity detection—a mode that offers superior sensitivity for trace anions. This limitation has driven the adoption of organic polymer matrices, such as PS-DVB and EVB-DVB, which withstand pH 0–14 and are compatible with hydroxide eluents, enabling the analysis of weakly acidic anions like bromate and chlorate at regulatory levels (e.g., GB 5749—2022). However, polymer matrices often exhibit lower chromatographic efficiency compared to silica, necessitating advanced functionalization strategies to enhance selectivity and resolution.
This review addresses the bottleneck of achieving both high selectivity and high sensitivity in water anion analysis by systematically comparing matrix types and functionalization approaches. It critically evaluates how surface chemistry—such as the introduction of quaternary ammonium groups with hydrophilic spacers—can mitigate the trade-offs between pH stability and separation efficiency. By synthesizing recent advances, the paper provides a roadmap for designing next-generation stationary phases that meet the stringent demands of environmental monitoring, including the precise identification of trace pollutants in complex water matrices.
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LIU Haolin, XU Jingwei, SHEN Yifan, CHENG Shi, LI Aimin (2026). Progress in Design, Preparation and Application of Ion Chromatography Stationary Phases for Analysis of Anions in Water. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025121001
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Frequently Asked Questions
What are the primary limitations of silica-based stationary phases in ion chromatography for anion analysis, and how do polymer matrices overcome them?
Silica-based stationary phases have a narrow pH tolerance of 2–8, which restricts their use with common IC eluents, especially hydroxide solutions required for suppressed conductivity detection. This limitation results in lower sensitivity and applicability only to high-concentration samples. Polymer matrices such as PS-DVB and EVB-DVB offer pH stability from 0 to 14, allowing the use of strong acid or base eluents, which is essential for analyzing weakly dissociated anions and achieving high sensitivity in suppressed IC.
How does the functionalization of polymer matrices enhance the separation selectivity for anions in water?
Functionalization introduces specific ionic groups (e.g., quaternary ammonium) and can modify hydrophilicity and spatial arrangement. For instance, anion exchangers with dihydroxy-containing alkyl substitutes in quaternary ammonium groups exhibit increased hydrophilicity, which improves mass transfer and selectivity. Additionally, grafting functional layers with controlled hydrophilicity can fine-tune ion-exchange interactions, leading to better separation of anions with similar properties, such as bromate and chloride.
What are the practical implications of pH tolerance for eluent selection in ion chromatography?
A wide pH tolerance (e.g., pH 0–14) allows the use of hydroxide or strong acid eluents, which are necessary for suppressed conductivity detection. This detection mode significantly enhances sensitivity for trace anions, enabling compliance with stringent regulatory limits (e.g., bromate at 10 μg/L in drinking water). Polymer matrices with such tolerance are therefore preferred for environmental monitoring applications.
What are the trade-offs between organic polymer and inorganic (silica) matrices in terms of chromatographic performance?
Silica matrices generally offer higher chromatographic efficiency (e.g., theoretical plates) due to their rigid structure and well-defined pore size, but they are limited to pH 2–8. Polymer matrices are more chemically stable across a wide pH range but may have lower efficiency due to swelling or less uniform particle size. However, advances in polymer synthesis have improved their performance, making them viable for high-efficiency separations.
How does the review address the need for high-throughput monitoring of trace pollutants in water?
The review discusses the development of novel stationary phases with high capacity and selectivity, which are essential for detecting trace pollutants in complex matrices. It also highlights the potential of hybrid materials and advanced functionalization to improve resolution and reduce analysis time, thereby enabling high-throughput monitoring. The integration of IC with mass spectrometry is noted as a future direction for enhanced sensitivity and specificity.
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