Determination of Total Cyanide in Municipal Wastewater and Drinking Water Using Ion-Exclusion Chromatography with Pulsed Amperometric Detection (ICE-PAD)

Importance of the Topic

Cyanide is a potent toxin that disrupts cellular respiration and poses significant environmental and public health hazards. Regulatory agencies such as the U.S. EPA strictly limit total cyanide in drinking water, surface water, and wastewater to protect aquatic ecosystems and human health. Reliable analysis of trace cyanide—encompassing free cyanide and complexed forms—is essential for compliance, risk assessment, and process control in industrial and municipal settings.

Objectives and Study Overview

This work presents a streamlined analytic approach for determining total cyanide in municipal wastewater effluent and drinking water. The goals were to combine ion-exclusion chromatography (ICE) with pulsed amperometric detection (PAD) using a platinum working electrode, eliminate common interferences (chloride, sulfate, sulfide), and integrate EPA-approved acid digestion via the MICRO DIST® system for direct, sensitive quantification of µg/L‐level cyanide.

Methodology and Instrumentation

• Sample Preparation: Acid distillation using the MICRO DIST® Cyanide‐1 kit. Samples (drinking water, wastewater effluent, certified standards) were stabilized with NaOH, digested with 7.11 M H₂SO₄/0.75 M MgCl₂ at 120 °C, trapped in 1 M NaOH, and diluted to 250 mM NaOH.
• Chromatography: Thermo Scientific Dionex ICS-3000 system with an ICE-AG1 guard column (4×50 mm) and ICE-AS1 analytical column (4×250 mm). Eluent: 50 mM methanesulfonic acid; flow rate: 0.2 mL/min; column temperature: 30 °C; injection volume: 50 µL.
• Detection: Pulsed amperometric detection (PAD) using a disposable platinum working electrode and pH–Ag/AgCl reference electrode. A multi-step waveform optimized for acid eluents was applied.
• Data Handling: Chromeleon 6.8 CDS for peak integration, virtual channel for pH monitoring, 375 µL reaction coil for improved signal stability.

Main Results and Discussion

• Separation Quality: Cyanide eluted at ~16 min with baseline resolution from sulfide (Rs>3). Strong acid anions (chloride, sulfate) were excluded by ICE, preventing coelution.
• Analytical Performance: Linearity over 1–25 µg/L (r²=0.9999). Limit of detection: 0.27 µg/L (99% confidence). Peak symmetry (As≈1.1) and stable background charge (70–120 nC).
• Precision and Accuracy: Replicate injections (n=6) of 5 µg/L cyanide yielded RSDs of 0.6–2.9%. Spike recoveries in drinking water, wastewater, and certified standard ranged from 97.4 to 102%.
• Interference Study: ASTM challenge matrix (ammonium chloride, cyanate, thiocyanate, nitrate, sulfate) generated false positives upon acid digestion, especially from cyanate and thiocyanate in the presence of nitrate. Pre-rinsing collector tubes reduced background contamination. Sulfide (up to 19 mg/L) did not interfere, thanks to the Pt electrode and ICE separation.

Benefits and Practical Applications

The ICE-PAD method offers direct determination of total cyanide without lengthy distillation apparatuses or titrations. Key advantages include minimal sample handling, reduced chemical interferences, low detection limits, and robust performance for environmental monitoring and industrial quality control, ensuring regulatory compliance and enhanced laboratory throughput.

Future Trends and Applications

• Automation and integration of sample preparation with IC systems to further increase throughput.
• Expansion to reagent-free IC platforms for consolidated anion analysis (cyanide, nitrate, thiocyanate).
• Development of novel electrode materials and waveforms for even lower detection limits.
• On-site and in-line monitoring using portable ICE-PAD instruments for real-time water quality assessment.

Conclusion

The combination of ion-exclusion chromatography with pulsed amperometric detection and MICRO DIST acid digestion delivers a fast, reliable, and sensitive method for total cyanide analysis in water matrices. It overcomes traditional interferences, achieves sub-µg/L detection limits, and meets rigorous regulatory requirements, making it a valuable tool for environmental monitoring and industrial analytics.

References

1. Simeonova P., Fishbein L. Hydrogen Cyanide and Cyanides: Human Health Aspects. Int. Chem. Assess. Doc. 61; UNEP/ILO/WHO: Geneva, 2004.
2. U.S. Department of Health and Human Services, ATSDR. Toxicological Profile for Cyanide; Atlanta, GA, 2006.
3. U.S. EPA Method 335.2. Determination of Total Cyanide in Water. EPA/600/4-79-020, 1980.
4. U.S. EPA Method 335.3. Determination of Total Cyanide by UV Digestion. EPA/600/4-79-020, 1978.
5. U.S. EPA Method 335.4. Total Cyanide Determination with UV Digestion. EPA/600/R-93/100, 1993.
6. Weinberg H.S., Cook S.J. Segmented Flow Injection and Amperometric Detection for Total Cyanide. Anal. Chem. 2002, 74, 6055–6063.