Traces of lithium and sodium besides monoethanolamine in water-steam circuits of thermal power plants

Significance of the topic

Maintaining the chemical balance of boiler feed water in thermal power plants is essential to avoid corrosion, scale formation and equipment damage. Monitoring key cations such as lithium, sodium and amine-based inhibitors ensures effective protection of the water-steam circuit and early detection of leaks or process upsets.

Objectives and Study Overview

This application note demonstrates a robust ion chromatographic method for the simultaneous quantification of trace lithium and sodium alongside high-level monoethanolamine in synthetic boiler feed water. The goal is to achieve sub-µg/L detection limits for alkali metals while accurately measuring amine concentration for corrosion control.

Methodology

The method employs ion chromatography with conductivity detection after sequential chemical suppression. Metrohm’s intelligent Preconcentration Technique combined with Matrix Elimination (MiPCT-ME) is used to enrich analytes from a 1 mL injection volume and remove interfering matrix components. A Metrosep C Supp 1 column series separates cations under a nitric acid eluent, while rubidium serves as an internal standard. Calibration covers a wide concentration range from 0.025 to 40 µg/L.

Used Instrumentation

• 940 Professional IC Vario ONE/SeS
• IC Conductivity Detector
• 858 Professional Sample Processor with MiPCT-ME module
• Dosino dosing units (3×800)
• 941 Eluent Preparation Module
• ELGA PURELAB Flex 6 for ultrapure water supply
• MSM-HC rotor and coated steel needle for precise sample handling

Results and Discussion

Under the optimized conditions (flow rate 1.0 mL/min, column temperature 40 °C, recording time 10 min), lithium and sodium are detected at 0.5 µg/L with relative standard deviations of 0.7 % and 1.3 %, respectively. Monoethanolamine at 4000 µg/L is quantified without suppression. The preconcentration factor of 40 enables a practical detection limit down to 0.025 µg/L for all cations.

Benefits and Practical Application

This combined MiPCT-ME and IC approach delivers high sensitivity, excellent reproducibility and efficient matrix removal without extensive sample preparation. Power plant operators can use this method for routine water chemistry control, early leak detection and compliance with corrosion management protocols.

Future Trends and Opportunities

Advancements may include real-time on-line monitoring, expansion to other corrosion inhibitors and trace metals, integration with digital data platforms for predictive maintenance and coupling with mass spectrometric detectors for enhanced selectivity.

Conclusion

The presented ion chromatographic method offers a reliable, sensitive and automated solution for simultaneous monitoring of trace lithium, sodium and monoethanolamine in boiler feed water, supporting proactive corrosion control in thermal power plants.