Fast Cap IC Determinations of Inorganic Anions and Cations in Drinking Water

The determination of common inorganic anions and cations in drinking water is important due to the toxicity of anions (e.g., fluoride, nitrite, and nitrate) and secondary contaminants (e.g., chloride and sulfate) which can affect the water's aesthetics. Therefore, these secondary contaminants are monitored and primary contaminants regulated for compliance by the U.S. EPA and other agencies around the world.

Ion-exchange chromatographic determination of dissolved alkali and alkaline earth metals and ammonia in drinking water is another important application. Sodium is monitored under the U.S. EPA Safe Drinking Water Act, whereas ammonium is a required target analyte for wastewater discharge permits and is monitored in process wastewaters.

Figure 1: Anions in undiluted municipal drinking water. Column: Thermo Scientific Dionex IonPac AG19, AS19, Capillary, 0.4 mm. Eluent: KOH (RFIC-EG). Gradient: 15 mM (0–7 min), 15–60 mM (7–18 min). Flow Rate: 10 µL/min. Inj. Volume: 0.4 µL. Temp: 30 °C. Peaks: 1) Chloride 105.7 mg/L; 2) Nitrate 2.8 mg/L; 3) Sulfate 30.4 mg/L.

Capillary IC requires µL/min flow rates. Due to its low consumption of eluent, the system can remain on continuously, thereby eliminating the need for calibration prior to each use to provide a true walk-up system. The low flow rate leads to longer lifetime of consumables and smaller amount of waste, thereby reducing the overall cost of ownership.

Conditions and Sample Preparation

The experimental setup and the sample preparation procedures are described in Application Brief 133, Thermo Fisher Scientific, Inc. (formerly Dionex Corp.).

Figure 2: Cations in undiluted municipal drinking water. Column: Dionex IonPac™ CG12A, CS12A, Capillary, 0.4 mm. Eluent: MSA (RFIC-EG). Gradient: 6–65 mM (0–30 min). Flow Rate: 10 µL/min. Inj. Volume: 0.4 µL Temp: 40 °C. Peaks: 1) Sodium 3.25 mg/L; 2) Ammonium 0.11 mg/L; 3) Potassium 0.25 mg/L; 4) Magnesium 0.37 mg/L; 5) Calcium 2.89 mg/L.

Conclusion

All anions were separated and eluted within 13 min. The peak area relative standard deviations for each analyte was 0.6% when 60 injections were evaluated within 24 h. Capillary Reagent-Free™ IC redefines the workflow for IC analysis of inorganic anions and cations, providing enhanced mass sensitivity and ease of use. It is a fast and accurate solution for routine characterization of different water samples.

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