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

Significance of the topic

Alkanolamines such as diethanolamine (DEA) and triethanolamine (TEA) are widely used in surface finishing, wastewater treatment and acid gas scrubbing in refineries and gas plants. Reliable monitoring of these compounds is essential to maintain process efficiency, prevent environmental contamination and ensure product quality in metal etching and scrubbing operations.

Objectives and overview

This application update presents a rapid ion chromatography method with pulsed amperometric or electrochemical detection for simultaneous quantification of DEA and TEA in complex matrices. The goal is to provide high sensitivity, precision and throughput compared to traditional wet chemistry, gas chromatography or HPLC approaches.

Methodology and instrumentation

• Column: Dionex OmniPac PAX-500 analytical column with guard and separator.
• Eluent: Isocratic mixture of 150 mM NaOH with 5 % acetonitrile at 1 mL/min.
• Detector: PAD II or PED with gold working electrode and Ag/AgCl reference cell.
• Pulsed waveform: E1 = 0.08 V/T1 = 540 ms; E2 = 1.00 V/T2 = 420 ms; E3 = –0.08 V/T3 = 420 ms.
• Sample loop: 50 µL; samples and standards diluted in 150 mM NaOH to prevent acid-catalyzed degradation.
• Standards: 0.1 to 100 ppm in 150 mM NaOH, showing linearity (r² > 0.998).

Main results and discussion

• Baseline separation of DEA and TEA achieved in under six minutes under high pH conditions that suppress amine ionization.
• Calibration linearity across three orders of magnitude with r² > 0.998 for both analytes.
• Precision better than 3 % RSD at 70 ppm (n=374 replicates).
• Detection limit around 10 ppb by direct injection.
• Acetonitrile content controls retention times; on-line mixing recommended to avoid acetonitrile degradation in alkali.

Benefits and practical applications

This high-throughput IC-PAD/PED method enables continuous monitoring of amine concentration in refinery scrubber loops, early detection of leaks in wastewater and pond water, and precise control of etching baths in aerospace aluminum finishing. It reduces maintenance downtime, improves product consistency and mitigates environmental risks.

Future trends and opportunities

• Implementation of low-pressure gradient mixing to prevent acetonitrile breakdown.
• Automation and integration with process control systems for real-time monitoring.
• Extension to other alkanolamines and related basic compounds in petrochemical and pharmaceutical applications.

Conclusion

The described ion chromatography method with pulsed electrochemical detection offers a robust, sensitive and rapid solution for quantifying DEA and TEA in diverse industrial and environmental samples, surpassing conventional approaches in speed, accuracy and ease of operation.

References

• Johnson D.C.; LaCourse W.R. Anal. Chem. 1990, 62, 589A–596A.
• Burwell K.F.; Dubek D.J.; Sigmund P.W. Hydrocarbon Processing, March 1982, 108–116.
• Keaton M.M.; Bourke M.J. Hydrocarbon Processing, August 1983.
• Campbell D.C.; Carson S.; Heberling S.; Bramer D.V. Improved Separation and Detection of Alkanolamines using Liquid Chromatography and Electrochemical Detection. Journal of Chromatography, Submitted.