Determination of Morpholine, Ethanolamine, and Hydrazine in Simulated Nuclear Power Plant Wastewater

Importance of the Topic

Corrosion control in nuclear power plant (NPP) secondary and cooling systems is critical to maintain plant reliability and safety. Organic amines such as morpholine, ethanolamine, and hydrazine are routinely used as pH control agents and oxygen scavengers but accumulate in wastewater along with high levels of ammonium and other cations. Regulatory limits require sensitive µg/L-level monitoring in complex high-salt matrices, creating a significant analytical challenge.

Objectives and Study Overview

This work describes development and validation of two high-performance ion chromatography (HPIC) methods using reagent-free IC with eluent generation (RFIC-EG) to determine:

• Hydrazine and morpholine simultaneously via a high-capacity IonPac CS16 cation-exchange column with a methanesulfonic acid (MSA) gradient, dual detection by suppressed conductivity and integrated pulsed amperometric detection (IPAD).
• Ethanolamine on an IonPac CS15 column using isocratic 5 mM MSA at elevated temperature with suppressed conductivity detection.

Methodology and Instrumentation

Sample Preparation:

• Simulated NPP wastewater prepared with 50 mg/L each of ammonium, sodium, calcium, magnesium, 10 mg/L potassium, and 1 mg/L lithium.
• Spiking of analytes in matrix for recovery and precision studies.

Hydrazine and Morpholine Method:

• Instrument: Dionex ICS-3000 with dual gradient pump, EG module (EluGen™ EGC II MSA), CR-CTC II trap, CSRS® 300 suppressor, conductivity and electrochemical detectors, AAA-Certified™ Au electrode.
• Column: IonPac CG16/CS16 (3 × 250 mm).
• Eluent: 15 mM to 65 mM MSA gradient inline by RFIC-EG.
• Postcolumn reagent: 50 mM NaOH at 0.14 mL/min for IPAD at pH ~12.2.
• Detection: Suppressed conductivity (77 mA) and IPAD with amino-acid waveform.
• Run time: 32 min; injection volume: 25 µL; column temperature: 40 °C.

Ethanolamine Method:

• Instrument: Dionex ICS-3000 configured with EG-RFIC, CR-CTC II, CSRS 300, conductivity detector.
• Column: IonPac CG15/CS15 (2 × 250 mm) at 50 °C.
• Eluent: 5 mM MSA isocratic via RFIC-EG; flow rate 0.3 mL/min.
• Detection: Suppressed conductivity (recycle mode, 58 mA).
• Run time: 18 min; injection volume: 5 µL.

Main Results and Discussion

Limits of detection (3× S/N) and quantification (10× S/N) were determined using blank noise measurements:

• Hydrazine: LOD 2.3 µg/L, LOQ 8.6 µg/L (linear 10–50 µg/L, r² = 0.9997).
• Morpholine: LOD 24.8 µg/L, LOQ 147 µg/L (linear 150–500 µg/L, r² = 0.9997).
• Ethanolamine: LOD 13 µg/L, LOQ 54 µg/L (linear 50–800 µg/L, r² = 0.9997).

In matrix spike experiments:

• Hydrazine (20 µg/L): recovery 109%, retention time RSD <0.1%, area RSD 1.9%.
• Morpholine (200 µg/L): recovery 97%, retention time RSD <0.1%, area RSD 2.9%.
• Ethanolamine (200 µg/L) in 80% matrix dilution: recovery 102%, retention time RSD 0.4%, area RSD 1.8%.

Method robustness was demonstrated under minor variations in postcolumn reagent concentration, column temperature, suppressor regeneration, and electrode/column lots with <5% change in response for hydrazine and acceptable variation for morpholine under controlled PCR preparation.

Benefits and Practical Applications

• High sensitivity for regulatory compliance of NPP wastewater discharge permits.
• Reagent-free eluent generation reduces labor, improves reproducibility, and eliminates manual eluent preparation.
• Dual detection strategy enhances selectivity in complex salt matrices.
• Adaptable to routine QA/QC laboratories in power generation facilities.

Future Trends and Opportunities

• Integration of on-line sampling and automated RFIC systems for real-time monitoring.
• Miniaturization and microfluidic approaches to reduce solvent and sample consumption.
• Coupling with mass spectrometry for broader multi-analyte profiling.
• Application of novel stationary phases and detection modes for emerging corrosion inhibitors.

Conclusion

Two robust RFIC-EG methods have been established for the µg/L-level determination of hydrazine, morpholine, and ethanolamine in simulated nuclear power plant wastewater. The combination of inline eluent generation, suppressed conductivity, and IPAD detection provides high sensitivity, excellent reproducibility, and efficient throughput for compliance monitoring.

Used Instrumentation

• Dionex ICS-3000 system with DP dual gradient pump and EG module.
• EluGen™ EGC II MSA cartridge; CR-CTC II trap column; CSRS® 300 suppressor.
• DP detector with conductivity module; AS Autosampler with 10 mL tray.
• Electrochemical detector with AAA-Certified™ Au electrode.
• IonPac CS16 (3 × 250 mm) and CS15 (2 × 250 mm) columns; PEEK tubing and reaction coil assembly.

Reference

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