Determination of Chelating Agents in Drinking Water and Wastewater Samples

Importance of the Topic

The widespread use of aminopolycarboxylate chelating agents such as EDTA, NTA, DTPA and EGTA in domestic and industrial processes makes them critical to control metal-catalyzed reactions in cleaning, paper production and agriculture. Persistent chelates like EDTA and DTPA can accumulate in wastewater, disrupting treatment and harming ecosystems, and are subject to regulatory limits, underscoring the need for sensitive monitoring methods.

Objectives and Study Overview

This work presents a direct, sensitive ion chromatography method with pulsed amperometric detection to quantify µg/L levels of four aminopolycarboxylate chelating agents in drinking water, surface water and municipal wastewater effluent, aiding compliance with environmental standards.

Methodology and Instrumentation

A high-capacity IonPac AS7 column with a CTC-1 trap column was used to separate chelates using a methanesulfonic acid gradient (35–100 mM) in 16 minutes. Detection employed pulsed amperometry on a platinum working electrode and Ag/AgCl reference in a Dionex ICS-3000 or ICS-5000 system controlled by Chromeleon software.

Used Instrumentation

• Dionex ICS-3000/ICS-5000 with SP pump, degasser, DC/DC modules and AS autosampler
• ED electrochemical detector with Pt working electrode and pH-Ag/AgCl reference
• IonPac CTC-1 guard trap and IonPac AG7 and AS7 analytical columns
• Chromeleon chromatography data system
• Vacuum filtration units and 0.2 µm syringe/membrane filters

Main Results and Discussion

Separation of EDTA, NTA, DTPA and EGTA was achieved with good peak symmetry and resolution. Limits of detection ranged from 15 to 63 µg/L and quantification from 50 to 210 µg/L. Calibration was linear up to 1000–4000 µg/L (r²>0.999). In real samples, EGTA was found at 0.13–0.18 mg/L in all matrices, while EDTA appeared only in wastewater effluents at 0.024–0.054 mg/L. Spiked recoveries ranged 89–112%. Matrix effects were mitigated by filtration, degassing, dilution, pH adjustment and OnGuard M cartridges. Iron strongly bound EDTA and DTPA, altering retention and response; combined base treatment, heating and OnGuard M treatment improved EDTA recovery.

Benefits and Practical Applications

• Selective, direct µg/L determination of chelating agents in complex water matrices
• Minimal interference from common anions
• Meets regulatory requirements for water quality monitoring
• Adaptable to routine environmental analysis workflows

Future Trends and Opportunities

Future developments may include on-line sample cleanup, coupling to mass spectrometry for simultaneous metal–chelate speciation, expansion to other chelators and enhanced automation for high-throughput environmental monitoring.

Conclusion

The described ion chromatography method with pulsed amperometric detection provides a robust, sensitive and accurate approach for monitoring aminopolycarboxylate chelating agents at µg/L levels in drinking water, surface water and wastewater, supporting environmental safety and regulatory compliance.

Reference

1. Sillanpaa M, Sihvonen M. Talanta 1997,44,1487–1497.
2. WHO. Guidelines for Drinking-Water Quality, Addendum, 2003.
3. Grundler OJ et al. ACS Symp Ser 2005,910,336–347.
4. Bedsworth WW, Sedlak DL. ACS Environ Chem Div 2000.
5. Nortemann B. ACS Symp Ser 2005,910,150–169.
6. Lugauskas A et al. Ekologija 2005,1,61–69.
7. Schmidt C, Brauch HJ. Environ Toxicol 2004,19(6),620–637.
8. Fitzgerald GP, Faust SL. Appl Microbiol 1993,11,345–351.
9. German Federal Institute of Occupational Safety, 2004.
10. Cheng J et al. J Electroanal Chem 2007,608,117–124.
11. Dionex IonPac AS7 Manual 2008.
12. Dionex ED Manual 2004.
13. Dionex Application Note 188,2008.
14. Weiss J. Handbook of Ion Chromatography 2004,181–185.
15. Dodi A, Bouscarel M. LCGC Europe 2006.
16. Ammann A. J Chromatogr 2002,947,205–216.
17. Cheng J, Jandik P. LCGC 2006,53.