Determination of Trace Sodium and Transition Metals in Power Industry Samples by Ion Chromatography with Nonsuppressed Conductivity Detection

Importance of the topic

Continuous monitoring of ultratrace ionic impurities in power plant water cycles is critical to prevent corrosion, stress‐corrosion cracking and costly outages. Amine treatments such as ethanolamine raise pH and purity but complicate low‐ppt sodium analysis. Transition metals (Fe, Cu, Zn, etc.) also influence corrosion and radiation dose, driving demand for sensitive on‐line ion chromatography methods.

Objectives and study overview

This work evaluates nonsuppressed conductivity detection versus suppressed conductivity for (1) sub‐ppb sodium quantification in boiler water treated with ethanolamine and (2) detection of transition metals by postcolumn complexation. Key metrics include calibration linearity, detection limits and spike recoveries in simulated power‐industry matrices.

Methodology

Samples with 3–5 ppm ethanolamine were spiked with 0.25 ppb sodium and loaded (3 mL) onto a 4 × 35 mm TCC-LP1 concentrator. Separation used a 4 × 250 mm IonPac SCG 1 column with 3 mM methanesulfonic acid eluent at 1 mL/min and 30 °C. Nonsuppressed conductivity detection was performed directly. Transition metals were separated on SCG 1 with oxalic/tartaric acid eluents in 3–25 µL injections, detected by nonsuppressed conductivity.

Used instrumentation

• ICS-1000/1500/2000 Ion Chromatography System
• DXP single-piston pump
• 4 × 250 mm IonPac SCS 1 analytical column & 4 × 50 mm SCG 1 guard column
• 4 × 35 mm TCC-LP1 preconcentrator column
• Non-suppressed conductivity detector
• Column heater
• Digital conductivity detector

Main results and discussion

Nonsuppressed detection achieved an MDL of 68 ppt sodium (3 mL load) with r2=0.9998 over 100–500 ppt. Suppressed conductivity reaches ~3 ppt (10 mL load). Recoveries of 250 ppt sodium in 3 ppm and 5 ppm ethanolamine were 97% and 93%, respectively. High amine loads limit concentrator breakthrough to ~4.5 mL. Transition metals (Cu, Zn, Co, Mn, Cd) were resolved on SCG 1 with oxalic/MSA eluents; MDLs of 33 ppb (Cu) and 6.7 ppb (Zn) for 25 µL injections.

Benefits and practical applications

Nonsuppressed IC simplifies hardware by removing the suppressor and supports simultaneous conductivity detection of alkali and transition metals. It enables on-line sub‐ppb sodium monitoring in amine‐treated waters and routine screening of transition metals for corrosion management.

Future trends and potential applications

Advances in high-capacity concentrator resins and low-noise detectors may improve nonsuppressed sensitivity toward suppressed levels. New complexing eluents and compact IC designs will enhance real-time corrosion monitoring and integration with digital power-plant analytics.

Conclusion

Nonsuppressed conductivity IC offers a practical route for trace sodium in moderate ionic-strength samples and multispecies transition metal screening. While suppressed conductivity retains superior sensitivity for high-strength matrices, nonsuppressed detection reduces system complexity and enables broad analyte coverage.

References

1. Electric Power Research Institute. In-Plant System for Continuous Low-Level Ion Measurement in Steam Producing Water. EPRI Report RP1447-1, Palo Alto, CA, 1994.
2. Bostic D.W., Burns G., Harvey S.J. Journal of Chromatography 1992, 602, 163–171.
3. Newton B. PowerPlant Chemistry 2002, 4(5), 297–299.
4. Dionex Corporation. Application Note 152. Sunnyvale, CA.
5. Dionex Corporation. Application Note 157. Sunnyvale, CA.