Online analysis of trace cations in power plant water matrices

Significance of the topic

Online, contamination-free sampling of power plant water is essential for reliable monitoring of ion concentrations. By integrating automated inline sample preparation and simultaneous anion/cation analysis, plants can ensure rapid quality control and comply with regulatory standards. This approach enhances throughput and minimizes manual handling errors.

Study Objectives and Overview

The application note demonstrates a setup for concurrent determination of anions and cations in boiler water using Ion Chromatography (IC). It focuses on combining variable preconcentration (MiPCT) with inline calibration to streamline analysis in a single run. Anion results are detailed in a companion note, while this note outlines the cation workflow and performance metrics.

Methodology and Instrumentation Used

• Sample Preparation: Online sampling lines directed to separate anion and cation analysis streams, avoiding cross-contamination.
• Preconcentration: MiPCT technique enabling adjustable preconcentration factors through selective trapping on Metrosep C columns and guards.
• Calibration: Single multi-ion standard adjusted across seven levels (0.5–10 µg/L) via precise dosing volumes.
• Eluent System: Inline generated eluent (2.5 mmol/L HNO₃, 0.5 mmol/L oxalic acid) using ultrapure water; automated via Dosino and level control units.
• Detection: Direct conductivity detectors with sensitive measurement of separated cations.
• Chromatography Conditions: Flow rate 0.4 mL/min, injection volume 9.8 mL, column temperature 32 °C, run time 19 min.

Main Results and Discussion

The method delivered consistent quantification of eight cations in artificial boiler water over 78 h:

• Recovery and repeatability for Cu, Ni, Na, Zn, K, Ca, and Mg within ±2% mean deviation, RSDs below 6%.
• Ammonium was not quantifiable under tested conditions.
• High preconcentration factors facilitated detection at sub-µg/L levels.

The stable performance demonstrates robustness of inline preparation and calibration, with minimal drift over extended runs.

Practical Benefits and Applications

• Reduces manual sample handling and risk of contamination.
• Simultaneous anion/cation analysis improves lab efficiency.
• Variable preconcentration adapts to different ion concentration ranges.
• Automated calibration minimizes standard preparation time and errors.

Future Trends and Potential Applications

Advancements may include integration with advanced detectors (e.g., mass spectrometry coupling) for enhanced selectivity, real-time data analytics for process control, and broadened application to other industrial water matrices. Further miniaturization of inline modules could support decentralized monitoring in remote sites.

Conclusion

The presented IC setup with inline sample preparation and calibration offers reliable, high-throughput analysis of cations in power plant water. Robust performance over long runtimes underscores its suitability for routine quality control.

Used Instrumentation

• Metrohm 850 Professional IC AnCat – MCS
• IC Conductivity Detectors (2 ×)
• 872 Extension Modules for Liquid Handling (2 ×)
• 800 Dosino Liquid Handling Units (2 ×)
• 849 Level Control for Inline Eluent Preparation (2 ×)