Fast Analysis of Anions in Drinking Water by Ion Chromatography

Importance of the Topic

Reliable measurement of inorganic anions such as fluoride, chloride, nitrite, nitrate, phosphate, bromide and sulfate in drinking water is essential to protect public health and to meet regulatory standards. Fast, accurate and sensitive methods help laboratories maintain compliance with U.S. EPA limits and detect trace contaminants that affect water quality and consumer safety.

Objectives and Study Overview

This study evaluates a high-throughput ion chromatography method using the narrow-bore IonPac AS14A (3 mm) column coupled with an Atlas electrolytic suppressor for the routine analysis of common inorganic anions in drinking water. Key goals include reducing analysis time, improving sensitivity and demonstrating long-term stability under typical environmental monitoring conditions.

Methodology and Instrumentation

Reagents and Eluent Preparation
• 8.0 mM sodium carbonate/1.0 mM sodium bicarbonate eluent prepared from a 100× concentrate in degassed Type I water

Sample and Standard Preparation
• Seven anion standards (fluoride, chloride, nitrite, bromide, nitrate, phosphate, sulfate) at five calibration levels (0.1–100 mg/L)
• Laboratory fortified blanks (LFB) and fortified matrices (LFM) at typical drinking water concentrations to assess recovery

Used Instrumentation

• Dionex DX-600 ion chromatograph with GS50 or GP50 gradient pump
• AS40 autosampler (25 µL injections) and LC30 column oven at 30 °C
• IonPac AS14A analytical column (3×150 mm) with AG14A guard (3×30 mm)
• Atlas electrolytic anion suppressor (AES) operating in recycle mode at 45 mA
• Suppressed conductivity detection via ED50A or CD25A

Main Results and Discussion

• Run time shortened to 6 min per injection at 0.8 mL/min, increasing daily throughput to over 200 samples.
• Baseline noise with Atlas suppressor (1.2 nS) was substantially lower than with ASRS-ULTRA (9.4 nS), yielding detection limits of 0.8–10 ppb versus 6–74 ppb.
• Calibration linearity (r2 ≥ 0.997) across relevant concentration ranges and stable response factors (1.0–2.3% RSD) over 6 days.
• Excellent precision for mid-level analytes (chloride and sulfate ~1% RSD) and acceptable repeatability at trace levels (fluoride ~5.5% RSD, bromide ~14% RSD at near-LOD).
• Recoveries in deionized water (96–103%) and actual drinking water matrices (92–102%) met or exceeded EPA method criteria.
• Seasonal variations in real drinking water samples (Sunnyvale, Palo Alto, Twain Harte) were effectively monitored, with fluoride levels ranging from 0.05 to 0.73 mg/L and other anions quantified accurately.

Benefits and Practical Applications

• High throughput: up to 203 injections per day reduces backlog and operational costs.
• Enhanced sensitivity: lower detection limits enable trace contaminant monitoring.
• Robustness: stable retention times and responses over extended operation periods.
• Regulatory compliance: meets U.S. EPA Method 300.0 performance requirements.

Future Trends and Potentials

Further improvements in column materials, suppressor technology and low-noise detection will continue to drive faster separations and even lower detection limits. Integration with automated data processing and remote monitoring will enhance laboratory efficiency and support real-time water quality surveillance.

Conclusion

The combination of a narrow-bore AS14A column and an Atlas electrolytic suppressor delivers a rapid, sensitive and reliable method for the routine analysis of inorganic anions in drinking water, providing high throughput and robust performance aligned with regulatory standards.

Reference

• U.S. EPA Method 300.0, The Determination of Inorganic Anions in Water by Ion Chromatography, U.S. EPA EMSL, Cincinnati, OH.
• Jackson PE et al., J. Chromatogr. 2001, 920, 51–60.
• Small H, Riviello J, Anal. Chem. 1998, 70(11), 2205–2212.