The Determination of 10 Anions in EPA Method 300.1 using Shimadzu High-Resolution Ion Chromatography

Importance of the Topic

Reliable monitoring of inorganic anions in drinking and environmental waters is essential for public health protection and regulatory compliance. Common anions (fluoride, chloride, nitrate, etc.) and potentially harmful disinfection by-products (chlorite, bromate) must be quantified accurately at trace levels to ensure water safety and meet stringent maximum contaminant levels (MCLs).

Objectives and Overview of the Study

This work extends previous efforts on EPA Method 300.1 Part A analysis by presenting two high-resolution ion chromatography (IC) methods capable of simultaneous determination of ten anions, including both common species and DBPs listed under EPA Method 300.1. The goals were to develop robust protocols for:

• High-resolution separation of bromide and chlorate for trace-level DBP analysis
• Rapid analysis suitable for routine monitoring
• Demonstration of linearity, detection limits, reproducibility, and accuracy in various water matrices

Methodology and Instrumentation

Instrumentation:

• Shimadzu modular IC system: CBM-40 controller, DGU-403 degasser, LC-20Ai pump (auto-rinsing), SIL-20AC autosampler (inert kit), CTO-40S column oven with suppressor kit, CDD-10Avp conductivity detector, ICDS-40A electrodialytic suppressor
• Software: LabSolutions chromatography
• Analytical column: Shodex IC SI-52 4E (4 × 250 mm) with Shodex SI-90G guard (4.6 × 10 mm)

Eluent preparation:

• Stock: 0.18 M Na₂CO₃ and 0.17 M NaHCO₃ in deionized water
• Method 1 eluent: 2.7 mM Na₂CO₃ / 5.1 mM NaHCO₃
• Method 2 eluent: 5.4 mM Na₂CO₃

Method conditions:

• Flow rate: 0.8 mL/min; Column temperature: 50 °C; Suppressed conductivity (60 mA recycle); Backpressure ~1450 psi
• Injection volumes: 50 μL (Method 1), 10 μL (Method 2)

Results and Discussion

Separation performance:

• Both eluents achieved baseline separation of ten anions.
• Method 1: longer run time (<20 min) but enhanced resolution of bromide vs. chlorate, beneficial for trace DBP analysis.
• Method 2: complete separation within 20 min, suited for high-throughput screening.

Linearity and detection limits (Method 1):

• Calibration coefficients of determination (R²) > 0.999 over broad concentration ranges
• Method detection limits (MDLs) calculated per EPA 300.1 protocol ranged in the low ppb region

Reproducibility:

• Retention time RSD: 0.02–0.08 %
• Peak area RSD: 0.23–0.42 %

Accuracy in real matrices:
Acceptable recoveries were obtained for all anions spiked into bottled, dispenser, and tap water using both methods, demonstrating robustness across water types.

Benefits and Practical Applications

These methods enable water quality laboratories to:

• Simultaneously quantify common anions and DBPs with a single injection
• Choose between high-resolution analysis (Method 1) or rapid throughput (Method 2)
• Ensure compliance with EPA regulatory limits and support QA/QC activities

Future Trends and Applications

Advances in electrolytic suppressor technology and column chemistry may further reduce analysis times and detection limits. Potential developments include:

• Integration of automated sample preparation for complex matrices
• Miniaturized IC systems for field or on-site monitoring
• Coupling with mass spectrometry for enhanced selectivity of organic by-product screening

Conclusion

The Shimadzu high-resolution IC system with electrolytically regenerated suppression provides reliable, reproducible, and sensitive determination of ten inorganic anions as specified in EPA Method 300.1. Method 1 excels in resolving trace-level DBPs, while Method 2 offers rapid routine analysis, supporting diverse water testing scenarios.

References

1. EPA Method 300.0: Determination of Inorganic Anions by Ion Chromatography.
2. EPA Method 300.1: Determination of Inorganic Anions in Drinking Water by Ion Chromatography.