Rapid Analysis of Seven Common Anions in Water Using Suppressed Conductivity IC

Significance of the Topic

This application note addresses the rapid determination of seven priority inorganic anions in water, defined in EPA Methods 300.0 and 300.1. Accurate measurement of fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulfate is critical for environmental monitoring, regulatory compliance and water quality management.

Study Objectives and Overview

The primary goal was to develop and validate a high-throughput suppressed conductivity ion chromatography (IC) method capable of separating all seven anions in under 8 minutes. The approach leverages a short, high-efficiency column and an electrolytically regenerated suppressor to maintain robustness and reproducibility for routine water analysis.

Methodology and Instrumentation

Eluent was prepared by mixing 0.36 mM sodium carbonate with 5.1 mM sodium bicarbonate. Samples and calibration standards were made by diluting 1000 ppm stock solutions into degassed deionized water (≥18.0 MΩ·cm). Key method parameters:

Flow rate: 0.4 mL/min
Column temperature: 40 °C
Injection volume: 20 µL
Suppressor current: 180 mA (external water regeneration at 1.0 mL/min)
System backpressure: ~1450 psi
Background conductance: ~25 µS/cm; noise <1 nS/cm peak-to-peak

Used Instrumentation

• Shimadzu modular LC system: CBM-40 controller, DGU-403 degasser, LC-20Ai pump, SIL-20AC autosampler, CTO-40S column oven
• ICDS-40A electrodialytic suppressor with suppressor installation kit
• CDD-10Avp suppressed conductivity detector
• Shodex IC SI-35 2B analytical column (2 × 50 mm) with IC SI-2GF guard filter
• LabSolutions chromatography data system

Results and Discussion

Separation of all seven anions was achieved in under 8 minutes using the short column format. Calibration across 0.1–10 ppm exhibited excellent linearity (R² >0.9999). Method precision was evaluated with eight replicate injections of mixed standards (0.5 ppm for F⁻, NO₂⁻, NO₃⁻, Br⁻; 1 ppm for Cl⁻, PO₄³⁻, SO₄²⁻). Retention time RSDs ranged from 0.02% to 0.08%; peak area RSDs were between 0.23% and 0.37%, demonstrating high reproducibility and stability under rapid analysis conditions.

Benefits and Practical Applications

• High throughput: complete separation in 8 minutes accelerates sample turnaround
• Robust suppressed conductivity detection yields low background and noise
• Reliable linearity and precision meet regulatory requirements for water quality monitoring
• Electrolytically regenerated suppressor reduces maintenance and reagent consumption

Future Trends and Potential Applications

Advancements in microbore and monolithic columns may further reduce analysis times and solvent consumption. Integration with mass spectrometric detection could enable simultaneous trace metal and anion profiling. Automation of sample preparation and inline dilution will support continuous monitoring applications in drinking water treatment and environmental compliance.

Conclusion

The described Shimadzu IC method provides a fast, precise and robust solution for quantifying seven key inorganic anions in water. Its combination of short analysis time, excellent performance metrics and low operational overhead makes it well suited for routine environmental and regulatory laboratories.

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, Rev. 1.0.
3. Shimadzu Application Note HPLC-021. Determination of EPA Method 300 anions using Shimadzu IC system.
4. Shimadzu Application Note HPLC-022. Determination of ten anions in EPA Method 300.1 using high-resolution IC.