Determination of Chelating Agents in Drinking Water and Wastewater Samples

Significance of the Topic

Chelating agents such as EDTA, NTA, DTPA and EGTA are extensively applied in detergents, pulp and paper production, agriculture and soil remediation. Their strong metal-complexing properties enhance process efficiency but also lead to environmental persistence, particularly for EDTA and DTPA. Monitoring of trace levels in drinking water and wastewater is essential to comply with regulatory limits and to protect ecosystems and human health.

Objectives and Study Overview

• Establish a sensitive and selective ion chromatography method to quantify aminopolycarboxylate chelators at µg/L to mg/L levels.
• Validate performance in municipal drinking water, surface water and treated effluent for regulatory and environmental monitoring.

Methodology and Instrumentation

The separation employs a Dionex IonPac AS7 high-capacity anion-exchange column with a methanesulfonic acid gradient (35–100 mM) over 16 min. Detection is by pulsed amperometry on a platinum working electrode. Samples are prefiltered, degassed, and, for wastewater, diluted (1:10) to mitigate matrix effects. Metal-chelate dissociation is enhanced by pH 11 adjustment, heating to 50 °C, filtration of metal precipitates and passage through a cation OnGuard M cartridge. Instrumentation includes the Thermo Scientific Dionex ICS-3000/5000 system, CTC-1 trap column, ED electrochemical detector and Chromeleon CDS.

Main Results and Discussion

• Limits of detection: 15–63 µg/L; limits of quantification: 50–210 µg/L; linearity r² > 0.999 over the calibrated ranges.
• Precision (n=7) for retention times <0.3% RSD; peak area precision 2–3.5% RSD.
• Recovery in spiked surface and drinking water samples ranged 89–112%.
• Wastewater required degassing, filtration and dilution to reduce baseline disturbances, achieving 95–101% recovery for EDTA and EGTA.
• Iron and copper formed complexes that altered retention and peak response; combined pretreatment restored EDTA quantification but DTPA recovery remained incomplete.

Benefits and Practical Applications

• Direct, derivatization-free quantification of aminopolycarboxylates at trace levels.
• High selectivity against common anionic interferences in environmental matrices.
• Applicable to routine monitoring in drinking water plants, wastewater treatment and environmental studies.

Future Trends and Opportunities

• Refinement of metal-chelate dissociation procedures to improve recovery of stronger complexes.
• Integration with mass spectrometric detection for enhanced specificity and identification.
• Development of automated sample preparation workflows for higher throughput and reproducibility.

Conclusion

The described IC-PAD method provides a fast, robust and accurate approach for monitoring NTA, EDTA, DTPA and EGTA in diverse water samples. Optimized pretreatment strategies mitigate matrix and metal-complexation effects, enabling reliable measurement at levels relevant to environmental regulation and public health.

References

• Sillanpää M, Sihvonen M. Analysis of EDTA and DTPA. Talanta. 1997;44:1487–1497.
• World Health Organization. Edetic Acid (EDTA) in Drinking-Water. WHO Guidelines for Drinking-Water Quality Addendum. 2003.
• Grundler OJ, van der Steen ATM, Wilmont J. Overview of the European Risk Assessment on EDTA. In: Nowack B, VanBriesen JM, editors. ACS Symposium Series 910. Washington, DC: American Chemical Society; 2005. p. 336–347.
• Bedsworth WW, Sedlak DL. Effects of EDTA on Pollutant Metal Removal by Wastewater Treatment. Presented at ACS Environmental Chemistry, 2000.