Determination of anions in tap water using US EPA method 300

Importance of the Topic

The determination of common anions in drinking water is critical to ensure compliance with regulatory limits set by the US EPA under the Safe Drinking Water Act and the Clean Water Act. Fast, reliable, and accurate measurements of fluoride, chloride, nitrite, bromide, nitrate, phosphate, and sulfate are essential for protecting public health and meeting increasing analytical demands.

Objectives and Study Overview

This study evaluates the performance of a Metrohm ion chromatography (IC) system for the analysis of seven anions in tap water according to US EPA Method 300 Part A. Key aims include achieving baseline separation within ten minutes, assessing method detection limits, and demonstrating workflow improvements through automated ultrafiltration and eluent production.

Methodology and Instrumentation

The separation was carried out on a Metrosep A Supp 5 - 100/4.0 column using an isocratic eluent of 3.2 mmol/L sodium carbonate and 1.0 mmol/L sodium bicarbonate at 0.8 mL/min. Chemical suppression was performed with a Metrohm suppressor regenerated by 500 mmol/L sulfuric acid. Calibration standards ranged from 0.04 to 2.0 mg/L for each anion. A three‐day method detection limit (MDL) study was conducted with seven replicate injections of 0.04 mg/L mixed standard. Inline Ultrafiltration was used to remove particles down to 0.2 µm, reducing carryover and column fouling. The 941 Eluent Production Module prepared eluent from a 20× concentrate, ensuring consistent retention times and minimal equilibration.

Instrumentation

• 930 Compact IC Flex ChS
• IC Conductivity Detector
• 800 Dosino and Dosino Regeneration modules
• 919 IC Autosampler Plus with Inline Ultrafiltration
• 941 Eluent Production Module
• Metrosep A Supp 5 - 100/4.0 analytical column with guard cartridge
• MagIC Net Compact software for data integration

Results and Discussion

Baseline separation of all seven anions was achieved in under ten minutes. Calibration curves exhibited excellent linearity (r² > 0.9999) and relative standard deviations below 2%. A comparison at 0.7 versus 0.8 mL/min demonstrated a reduction in sulfate retention time from 9.39 to 8.34 minutes at the higher flow rate. Tap water analyses (n=30) yielded average concentrations of 23.19 mg/L chloride, 5.89 mg/L nitrate, and 92.42 mg/L sulfate, with RSD values below 7%. MDLs calculated over three days met EPA Method 300.0/300.1 and 40 CFR Part 136 requirements. Inline Ultrafiltration effectively processed 200–300 samples per filter, maintaining low carryover (<0.1%) and prolonging column life.

Benefits and Practical Applications

The integration of automated ultrafiltration and eluent production streamlines sample preparation, reduces manual labor, and cuts operational costs. High sensitivity and low noise from chemical suppression allow smaller injection volumes, extending column longevity. The system is well suited for environmental laboratories handling low to high sample throughputs and supports routine compliance monitoring.

Future Trends and Opportunities

Advancements may include further automation of sample introduction, development of next‐generation suppressors for enhanced stability, and expansion of the method to trace anion species. Portable IC systems with integrated inline filtration and eluent modules could enable on‐site water quality testing.

Conclusion

The Metrohm IC configuration meets EPA Method 300 performance criteria for seven inorganic anions, delivering rapid separation, robust sensitivity, and reliable compliance data. Automated ultrafiltration and eluent production enhance laboratory efficiency and data quality.

References

• EPA Method 300.0: Determination of Inorganic Anions by Ion Chromatography
• EPA Method 300.1: Determination of Inorganic Anions in Drinking Water by Ion Chromatography, Revision 1.0