Determination of Ethanolamines in Industrial Waters by Cation-Exchange Chromatography

Importance of the Topic

Reliable detection of ethanolamine, diethanolamine, triethanolamine, and N-methyldiethanolamine is critical in petrochemical, environmental, and industrial water analysis. High concentrations of matrix amines can obscure trace-level analytes, demanding selective methods. Cation-exchange chromatography offers robust separation and quantification even in challenging samples.

Objectives and Overview of the Study

This work demonstrates an isocratic ion-exchange method to separate monovalent cations and four ethanolamines using a methanesulfonic acid eluent. The study evaluates linearity, detection limits, and performance in a refinery wastewater matrix spiked with varying amine concentrations.

Methodology and Chromatographic Conditions

Samples and standards are prepared in deionized water, with working solutions for cations (Li, Na, K, NH4) at 1000 mg/L and daily dilutions for ≤100 mg/L concentrations. Industrial waters are filtered (0.2 µm PEEK filters) and diluted if amine levels exceed column capacity. The eluent is 35 mM methanesulfonic acid, degassed by sonication under vacuum. Chromatographic conditions:

• Column: IonPac CS11 analytical (2 × 250 mm) with CG11 guard (2 × 50 mm)
• Eluent flow rate: 0.25 mL/min
• Injection volume: 2.5 µL
• Suppression: CSRS-II in external water mode at 100 mA
• Detection: suppressed conductivity

Instrumentation Used

The analysis employs a Dionex DX-500 ion chromatography system equipped with a GP40 pump (microbore), CD20 conductivity detector with DS3 cell, LC20 enclosure, Rheodyne sampling valve, and PEEK tubing. Optional Gelman Acrodisc ion-chromatography filters prevent particulate interference.

Main Results and Discussion

Under isocratic 35 mM MSA conditions, monovalent cations and four ethanolamines are baseline-resolved. A refinery wastewater sample diluted 1:1000 shows clear separation of ethanolamine, diethanolamine, and N-methyldiethanolamine. Spike recovery experiments in matrices containing 150 mg/L of a major amine yield calibration coefficients (r2) > 0.998 across relevant concentration ranges. Method detection limits: ethanolamine 0.055 mg/L; diethanolamine 0.15 mg/L; triethanolamine 1.1 mg/L; N-methyldiethanolamine 0.062 mg/L. Adequate sensitivity can be enhanced by increasing injection loop size, provided column capacity is maintained.

Benefits and Practical Applications of the Method

This procedure offers:

• High selectivity for ethanolamine derivatives in complex waters
• Low detection limits suitable for trace-level monitoring
• Robust performance in high-amine matrices without preconcentration
• Reproducible retention times and quantification for quality control

Future Trends and Potential Applications

Advancements may include on-line preconcentration or coupling with mass spectrometry to further lower detection limits. Miniaturized columns and gradient elution could shorten analysis time. Automated sampling and data processing will support real-time monitoring in industrial effluents and environmental surveillance.

Conclusion

The described cation-exchange method reliably quantifies ethanolamines in industrial waters, even against high background amine levels. It combines simple sample preparation with robust chromatography and suppressed conductivity detection for routine QA/QC and environmental analysis.

References

• Jensen D. LABO Analytica. 1992, 92, 64–74.
• Weiss J. Ion Chromatography, 2nd Ed. VCH, Weinheim, Germany, 1995, 182–185.