Cations and amines in the water-steam circuit

Significance of the topic

Corrosion in steel-based water–steam circuits poses a severe threat to the longevity and safety of power plants and industrial boilers. Maintaining pH slightly above neutral is essential to inhibit metal dissolution. Ammonium and organic amines are widely used for pH adjustment, but their simultaneous monitoring alongside inorganic cations (e.g., sodium, potassium, calcium, magnesium, nickel, zinc) demands robust analytical approaches.

Objectives and Study Overview

This application note demonstrates a single-run ion chromatographic method to separate and quantify typical inorganic cations and common amines in water–steam circuit samples. Key goals include:

• Achieving baseline separation of five inorganic cations (Na+, K+, Ca2+, Mg2+, Ni2+, Zn2+) and five amines (ammonium, ethanolamine, dimethylamine, morpholine, 3-methoxypropylamine).
• Implementing inline sample preconcentration and matrix elimination (MiPCT-ME) to enhance sensitivity at mg/L levels.
• Validating quantification down to 1 mg/L for all target analytes.

Methodology and Instrumentation

Sample preparation applies Metrohm’s Inline Preconcentration and Matrix Elimination (MiPCT-ME) strategy, reducing manual steps and matrix effects. Key parameters:

• Instrument: 850 Professional IC – Cation with conductivity detection; 858 Professional Sample Processor for automated handling; Dosinos and Level Control for inline eluent preparation.
• Columns: Metrosep C4 250/4.0 mm separation column with Metrosep C4 Guard and Metrosep C PCC 1 HC for preconcentration.
• Eluent: 2.5 mmol/L nitric acid and 0.5 mmol/L oxalic acid, generated inline.
• Flow rate: 0.9 mL/min; injection volume: 100 µL; column temperature: 32 °C; recording time: 30 min; backpressure up to 20 MPa.

Main Results and Discussion

A standard mixture containing all cations and amines at 1.0 mg/L yielded clear, well-resolved peaks within a 30-minute runtime. Inline preconcentration at a factor of 100 enabled detection limits near 0.01 mg/L. Chromatograms showed no significant interferences, demonstrating efficient matrix elimination.

Benefits and Practical Applications

This unified IC method offers several advantages:

• Simultaneous determination of inorganic and organic basic species in a single run.
• High sensitivity through automated inline preconcentration.
• Reduced sample handling and risk of contamination.
• Applicability for routine monitoring in power plant QA/QC and industrial process control.

Future Trends and Opportunities

Ongoing developments may include coupling IC with mass spectrometry for enhanced selectivity, expanding analyte panels to include neutralizing amines of emerging interest, and deploying real-time inline monitoring systems. Advances in column materials and microfluidic sample handling are expected to further streamline analyses.

Conclusion

The presented IC method with MiPCT-ME provides a reliable, sensitive, and automated solution for comprehensive monitoring of cations and amines in water–steam circuits. Its robustness and efficiency make it well suited for industrial quality assurance and research applications.

Reference

Metrohm Application Note C–139: Determination of cations and amines in water–steam circuits using inline preconcentration and matrix elimination.