Chemical disinfectants used to protect municipal drinking water from potentially dangerous microbes can produce disinfection byproducts – oxyhalides (chlorite, chlorate, bromate, etc.) that are harmful to humans. Therefore, routine analysis of inorganic anions and trace levels oxyhalides in a variety of sample matrices is required in many countries. In the U.S., these compounds are regulated by the Environmental Protection Agency (EPA).
History of column development for oxyhalides analysis
Thermo Scientific™ Dionex™ IonPac™ AS30, AS27, and AS19 columns are designed for the analysis of inorganic anions and oxyhalides using an isocratic or gradient elution with potassium hydroxide delivered with an eluent generator. All three columns use anion-exchange stationary phases based on hyperbranched condensation polymers prepared in situ on the surface of sulfonated ethylvinylbenzene-divinylbenzene substrate beads. While hyperbranched chemistry is responsible for high performance and selectivity, highly crosslinked substrates offer 0-100 percent organic solvent compatibility, which is important for cleaning the column from nonionic and hydrophobic contaminants or modifying column selectivity for special applications. Combination of substrate and coating chemistry also determines high hydrolytic stability of all hyperbranched columns in the entire pH range (0-14). Along with excellent separation of oxyhalides and inorganic anions, IonPac AS30, AS27 and AS19 columns provide good resolution between fluoride and water dip, which in turn allows large loop injection to improve the detection of oxyhalides to low ppb level without affecting the quantitation of fluoride.
IonPac AS19 column is a first-generation column developed for the analysis of oxyhalide disinfection byproducts using hydroxide eluent system. It is an excellent column for quantification of low ppb bromate, chlorite, and chlorate in the presence of high concentrations of chloride, sulfate, and carbonate. IonPac AS27, a second-generation column, was developed to improve the separation of fluoride from EDA carbamate. As described in EPA method 300.1, drinking water samples to be analyzed for bromate, chlorate and chlorite must be preserved with 50 mg/L ethylenediamine (EDA). However, EDA can react with carbonate and produce an artifact (EDA carbamate) that interferes with the early eluting analytes such as fluoride.
The more recent advances in hyperbranched technology and emerging market needs led to the development of a next-generation column, IonPac AS30, for the analysis of oxyhalides and common inorganic anions. This new column offers very high capacity to allow a direct injection of highly concentrated matrices without overloading the column and therefore an easy quantification of low ppb bromate, chlorite and chlorate. In addition, unique column selectivity significantly improves separation of fluoride from EDA carbamate as well as sulfate from carbonate, and as a result, provides better integration of fluoride and sulfate peaks while keeping the analysis time close to 35 minutes. Using an isocratic or gradient elution with potassium hydroxide, common inorganic anions and oxyhalides at ppb levels can be easily quantified in a variety of sample matrices including drinking water, wastewater, scrubber solutions, and process streams.
Comparison of Dionex IonPac AS30, AS27, and AS19 columns
All three columns, IonPac AS19, AS27, and AS30, provide exceptional performance and resolution for common inorganic anions and oxyhalides. Figure 1 demonstrates improved resolution of EDA carbamate and fluoride with IonPac AS30 column, as well as significantly better separation of carbonate and sulfate relatively to IonPac AS19 and AS27 columns in a simulated drinking water spiked with 50 ppm EDA. In addition, IonPac AS30 column maintains excellent separation of all other analytes within reasonable analysis time.
Evaluation of Dionex IonPac AS30 capabilities
Figure 2 demonstrates the separation of common inorganic anions and oxyhalides in municipal drinking water sample spiked with 50 ppm EDA and 5 ppb of bromate. A multistep gradient elution method was developed to achieve the desired separation without compromising the run time. The EDA carbamate artifact is well resolved from fluoride, so is carbonate from sulfate, which allows for easy quantification of these analytes.
As shown in Figure 3, despite the significantly higher concentration of matrix ions including chloride, carbonate, and sulfate (high ionic strength simulated matrix), bromate still can be detected at low ppb levels, and carbonate/sulfate resolution is not compromised.
Our evaluation demonstrated that IonPac AS30 is an excellent choice for the separation and quantitation of disinfection byproducts in water, especially for the samples preserved with EDA as per EPA method 300.1. The IonPac AS30 column delivers exceptional selectivity and much higher column capacity to allow large loop injections for trace analysis without sample pre-treatment or preconcentration and can be used for analysis of broad range of water samples.