Application of Eluent Generation for Trace Anion Analysis of Borated Waters

Importance of Topic

Boric acid is widely used in pressurized water reactor power plants as a neutron absorber to control nuclear reactions. Monitoring trace anionic contaminants such as fluoride, chloride, nitrate, phosphate, and sulfate in borated waters is critical for corrosion surveillance of stainless steel components. Even low-µg/L concentrations of these anions can accelerate stress-induced corrosion cracking in steam generators, boiler tubes, condenser tubes, and turbine blades.

Objectives and Study Overview

This application note describes a rapid, direct-injection ion chromatography method for determining trace anions in waters containing up to 7,500 mg/L boron. The goals were to eliminate manual eluent preparation, improve baseline stability during gradients, and achieve sub-µg/L detection limits. The study evaluated the performance of an on-line eluent generation system using boric acid as the carrier and an EG50 Eluent Generator to titrate potassium hydroxide in real time.

Methodology and Instrumentation

The system comprised a Dionex ICS-2500 IC with a GS50 gradient pump, CD25A conductivity detector, and EG50 eluent generator equipped with an EGC II KOH cartridge. A microbore IonPac AG14 guard and AS14 analytical column (2 mm i.d.) were used with an ASRS ULTRA II suppressor in external water mode. A high-capacity borate-form trap column (ATC-HC) was placed upstream of the eluent generator to remove anionic impurities in the boric acid stream. Elution employed a constant 50 mM boric acid carrier titrated to generate 4–30 mM KOH over an 18 min gradient at 0.38 mL/min. Samples and standards were directly injected (1 mL loop) after rigorous cleaning protocols to minimize contamination.

Main Results and Discussion

The combination of carbonate-free hydroxide eluents and constant boric acid background yielded a negligible baseline shift (<0.1 µS) over the gradient. Fluoride was well separated from organic acid interferences, and chloride retention was reproducible even in the presence of a large borate matrix peak. Calibration curves for all target anions were linear (r2 > 0.997) between 1 and 30 µg/L. Method detection limits ranged from 0.03 µg/L for fluoride to 0.32 µg/L for phosphate. Matrix spikes in 2,000 mg/L boron water showed comparable retention times and peak shapes to blanks.

Benefits and Practical Applications

• Eluent generation eliminates labor-intensive manual preparation and reduces operator variability.
• Microbore format enhances mass sensitivity fourfold and lowers reagent consumption.
• Carbonate-free KOH gradients improve baseline stability and peak integration.
• High trap-column capacity and automated suppression enable reliable trace-level quantification in high-boron matrices.

Future Trends and Potential Applications

Wider implementation of on-line eluent generation in routine QA/QC and industrial monitoring is expected to grow. Integration with advanced autosamplers and software control will further reduce contamination risks. Emerging suppressor technologies and novel eluent chemistries may expand trace-anion analysis to other challenging matrices such as radioactive or high-salinity waters.

Conclusions

The described IC method using eluent generation with boric acid and in-line KOH titration provides a robust, automated solution for trace anion analysis in borated waters. It combines excellent detection limits, minimal baseline drift, and high throughput, making it well suited for corrosion monitoring in nuclear power plant environments.

Reference

• 1. Electric Power Research Institute. Corrosion Fatigue Boiler Failures in Waterwall Economizers. EPRI TR-100455, Palo Alto, CA, April 1992.
• 2. Ling R.; Srinivasan K.; Saini S.; Pohl C.; Avdalovic N. Preparation of Tetraborate Eluents Using an EG50 Eluent Generator. Poster A-15, International Ion Chromatography Symposium, San Diego, CA, September 2003.
• 3. Liu Y.; Kaiser E.; Avdalovic N. Microchemical Journal, 1999, 62, 162–173.