Analysis of Inorganic Anions in Drinking Water According to EPA Method 300.1 Using Nexera IC Ion Chromatograph -Part B

Analysis of Inorganic Anions in Drinking Water (EPA Method 300.1) — Nexera IC

Significance of the topic

• Reliable quantification of inorganic anions (especially disinfection by-products) in drinking water is essential for regulatory compliance and public health protection.
• EPA Method 300.1 provides standardized procedures for ion chromatographic determination of common anions and inorganic disinfection by-products; robust implementation supports monitoring programs, treatment optimization and risk assessment.

Objectives and study overview

• Demonstrate suitability of the Nexera IC platform for analysis of four inorganic disinfection by-products (chlorite, bromate, bromide and chlorate) according to EPA Method 300.1 Part B.
• Optimize chromatographic conditions on the Shim-pack IC-SA3 column to achieve complete separation in less than 16 minutes.
• Verify method performance through method detection limits (MDL), linearity, spike recoveries, precision and long-term calibration stability.

Methodology

• Target analytes: chlorite (ClO2), bromate (BrO3), bromide (Br) and chlorate (ClO3) as specified in EPA Method 300.1 Part B. Bromide is measured both as a common anion and as a DBP precursor.
• Standards and samples: Six-point calibration standards prepared from commercial IC standard mixes; surrogate dichloroacetic acid (DCA) at 1 mg/L and ethylenediamine (EDA) as preservation solution at 50 mg/L were added to standards and samples. Analytical samples included tap water and two commercial mineral waters.
• Quality control: Determination of MDL by seven replicate analyses, evaluation of linearity (r2), spike recovery tests, and monitoring continuing calibration check standard (STD3) every ten samples over ~60 hours to assess calibration stability.

Analytical conditions

• Column: Shim-pack IC-SA3 with guard column Shim-pack IC-SA3 (G).
• Eluent: 4.5 mmol/L sodium carbonate; optimized for separation of the four DBP anions.
• Flow rate: 0.85 mL/min; Column temperature: 40 °C; Injection volume: 200 µL.
• Detection: Suppressed conductivity using an electrodialytic suppressor (ICDS-40Ai) and conductivity detector / CDD cell.
• Resulting runtime: complete separation and detection in under 16 minutes per injection.

Used instrumentation

• Nexera IC ion chromatograph (Shimadzu) configured with autosampler, pump, column oven and electrodialytic suppressor (ICDS-40Ai).
• Shim-pack IC-SA3 analytical column with Shim-pack IC-SA3(G) guard column.
• Conductivity detector / CDD cell for suppressed conductivity measurement.
• Consumables: Shimadzu LC vials (4 mL polypropylene) for sample handling.

Main results and discussion

• Linearity: Calibration curves for all four anions showed excellent linearity with coefficients of determination r2 ≥ 0.9996, exceeding EPA QC requirements.
• Method detection limits (MDLs): Calculated MDLs ranged from 0.3 to 0.6 µg/L (based on seven replicate analyses and Student’s t at 99% confidence), well below regulatory thresholds such as the bromate MCL and substantially lower than many target concentrations.
• Spike recoveries and precision: Fortified sample recoveries ranged 92–111% across tap and mineral waters, with %RSDs under ~1.6%, meeting EPA Method 300.1 acceptance criteria (75–125% for recoveries; surrogate DCA recoveries within 90–115%).
• Continuing calibration stability: The continuing calibration check (STD3) monitored over ~60 hours showed fluctuations within ±10% (100 ± 10%), well within the acceptable range (85–115%), demonstrating system stability for extended batch runs.
• Chromatographic performance: The optimized carbonate eluent and the Shim-pack IC-SA3 produced baseline separation of four DBP anions plus the DCA surrogate within a short runtime, aided by the electrodialytic suppressor which improved baseline and sensitivity.

Benefits and practical applications

• Regulatory compliance: The Nexera IC workflow meets EPA Method 300.1 Part B performance criteria for detection limits, linearity and recoveries, enabling confident compliance testing of drinking water.
• Throughput and robustness: Short analysis time (<16 min), low MDLs and high precision support routine monitoring and high-throughput laboratories.
• Flexibility: The method accommodates typical sample matrices (tap and bottled mineral waters) and surrogate/preservation additions recommended in EPA procedures.
• Improved sensitivity: Electrodialytic suppression reduces eluent background conductivity and enhances analyte response, improving detection of low-level DBPs such as bromate.

Future trends and potential uses

• Method extension: The validated fast separation could be adapted to include additional anions or organic DBP precursors with modified eluents or columns.
• Automation and remote monitoring: Integration with autosampling and networked LIMS could support large-scale monitoring programs and near real-time water quality surveillance.
• Lower detection limits: Advances in suppressor and detector technology may enable even lower MDLs to track trace-level DBPs and emerging contaminants.
• Combined workflows: Coupling IC with complementary detectors or mass spectrometry could provide orthogonal confirmation for complex matrices or regulatory disputes.

Conclusion

• The Nexera IC system with Shim-pack IC-SA3 and electrodialytic suppression successfully implements EPA Method 300.1 (Part B) for four inorganic DBP anions, delivering fast separations, low MDLs (0.3–0.6 µg/L), excellent linearity (r2 ≥ 0.9996), robust spike recoveries (92–111%) and stable calibration over extended runs.
• The platform is suitable for routine drinking-water monitoring, regulatory compliance testing, and laboratory workflows requiring high sensitivity and reproducibility.

References

1. U.S. Environmental Protection Agency. EPA Method 300.1: Determination of inorganic anions in drinking water by ion chromatography. Revision 1.0.
2. U.S. Environmental Protection Agency. National Primary Drinking Water Regulations. (2026-02).