Determination of Diethanolamine and Triethanolamine in Surface Finishing, Wastewater and Scrubber Solutions

Importance of the Topic

The accurate monitoring and quantification of diethanolamine (DEA) and triethanolamine (TEA) play a critical role in multiple industrial operations, including metal surface finishing, wastewater treatment, and acid gas scrubbing in oil refineries and natural gas plants.

Maintaining optimal concentrations of alkanolamines in scrubber solutions prevents salt overload, preserves gas-removal efficiency, and minimizes environmental contamination. In surface finishing, precise control of etchant chemistry ensures consistent aluminum and alloy processing.

Objectives and Study Overview

This work aims to develop a rapid, sensitive, and robust ion-chromatographic method for the simultaneous determination of DEA and TEA in complex matrices such as surface finishing baths, refinery wastewater, and scrubber solutions. Emphasis is placed on minimizing sample preparation time, enhancing detection limits, and reducing matrix interferences.

Methodology and Instrumentation

The method employs ion chromatography with a strong anion-exchange column operated under isocratic conditions and pulsed amperometric detection (PAD II or PED). Key parameters include:

• Column: Dionex OmniPac PAX-500 analytical column with guard
• Eluent: 150 mM NaOH blended online with 5% (v/v) acetonitrile
• Flow rate: 1.0 mL/min
• Detector waveform: three-step potential pulse (E1 = 0.08 V, E2 = 1.00 V, E3 = –0.08 V) with timing optimized for aminic analytes
• Sample preparation: dilution (1:100 to 1:1000) in 150 mM NaOH or direct injection after filtration for dilute waters
• Sample loop: 50 µL

Main Results and Discussion

Calibration curves prepared in 150 mM NaOH demonstrated excellent linearity (r^2 > 0.998) over 0.1–100 ppm for both DEA and TEA. Precision data from 374 replicate injections at 70 ppm yielded relative standard deviations below 3%. The method detection limit by direct injection was approximately 10 ppb in alkaline matrices.

Applied examples:

• Scrubber solution from an oil refinery: clear separation of DEA and TEA peaks within minutes, enabling on-site monitoring of amine performance.
• Surface etch bath: reliable quantitation of TEA at operational levels around 6 ppm.
• Pond water near refineries: direct analysis of environmental samples to track potential amine leaks.

Benefits and Practical Applications

The proposed approach offers the following advantages:

• Minimal sample preparation without derivatization, reducing analysis time to under 15 minutes.
• High sensitivity and selectivity for alkanolamines in challenging matrices.
• Reduced matrix interferences compared to colorimetric or gas-chromatographic methods.
• On-line mixing of reagents to prevent acetonitrile decomposition and maintain detector performance.

Future Trends and Opportunities

Advancements may include automated gradient elution systems for broader amine profiles, integration with online process analytics for real-time control, and miniaturized IC detectors for field deployment. Development of robust software algorithms for peak deconvolution and trending will further enhance predictive maintenance in refinery and finishing operations.

Conclusion

This ion-chromatographic method with pulsed amperometric detection provides a fast, precise, and sensitive solution for monitoring DEA and TEA across industrial and environmental applications. Its simplicity, reproducibility, and low detection limits support quality control and regulatory compliance in surface finishing, wastewater management, and gas scrubbing systems.

Reference

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