Beverages Applications Notebook - Drinking Water

Significance of the Topic

The accurate measurement of free cyanide in drinking water is critical due to cyanide’s acute toxicity and potential to form harmful by-products. Typical analytical methods require distillation, suffer interferences, and demand laborious sample preparation. A direct, reliable, and sensitive approach is needed to ensure compliance with regulatory limits and protect public health.

Objectives and Overview

This study presents a direct ion chromatography method using pulsed amperometric detection (PAD) for free cyanide in drinking water. The goals were to eliminate distillation steps, simplify sample preparation, achieve low‐µg/L detection limits, and demonstrate robustness against common matrix and metal interferences.

Instrumentation

• Dionex ICS-3000 Reagent-Free Ion Chromatography system (RFIC™)
• Dual or single gradient pump module with vacuum degas
• Detector/Chromatography module with electrochemical detector (ED)
• AS Autosampler with temperature control and 5 mL syringe
• Electrochemical amperometric cell with combination pH-Ag/AgCl reference electrode and disposable silver working electrode
• EG50 Eluent Generator with EGC II KOH cartridges and CR-ATC trap column
• OnGuard® II H cartridges for metal removal

Methodology

Samples were filtered (0.2 µm), preserved to pH 13 with NaOH, and, when required, treated with OnGuard II H cartridges to remove dissolved metals. A 10 µL full-loop injection was made onto an IonPac AS15 column with 63 mM NaOH eluent at 0.25 mL/min and 30 °C. The PAD waveform (E1 = –0.10 V, E2 = –1.00 V, E3 = –0.30 V vs Ag/AgCl) was applied to detect cyanide. Interferences from bromide, iodide, sulfite, thiocyanate, and thiosulfate were tested at 20 µg/L and found negligible. Metal interferences (Fe, Cu, Ni at 600 µg/L, 300 µg/L, 300 µg/L) reduced free cyanide unless removed by OnGuard II H cartridges.

Results and Discussion

– Calibration was linear from 2 to 100 µg/L cyanide (r² ≥ 0.999), with a practical quantitation limit of 1 µg/L (signal-to-noise ~16).
– Baseline noise was 7 ± 2 pC; retention time was 5.78 ± 0.03 min over 140 injections. Peak area reproducibility was 0.123 ± 0.002 nC·min.
– No significant interference from common anions; sulfide was detected but not coeluted.
– Copper and nickel complexes consumed cyanide (≤ 75% loss in 20 h); iron caused minimal loss (≤ 10% over 3 days). OnGuard II H treatment restored recoveries.
– Real drinking water samples showed variable native cyanide (often

Benefits and Practical Applications

This IC-PAD method enables direct free cyanide determination without distillation, with low detection limits, minimal matrix cleanup, and rapid analysis (25 min). The disposable silver electrodes and automated eluent generation increase ease of use and reproducibility. It is well suited for routine monitoring of municipal and bottled water supplies.

Future Trends and Possibilities

– Integration with on-line preconcentration for sub-µg/L sensitivity.
– Expansion to simultaneous multi-ion detection (e.g., sulfide, bromide) using optimized waveforms.
– Development of portable IC-PAD systems for field monitoring.
– Coupling with mass spectrometry or optical detectors for confirmatory analysis.

Conclusion

The direct IC-PAD method on the Dionex ICS-3000 with an AS15 column and HI eluent provides a fast, robust, and sensitive approach for free cyanide determination in drinking water. It overcomes limitations of traditional methods by eliminating distillation and minimizing interferences, while achieving an MDL of 1 µg/L and excellent precision and recovery.

References

• National Research Council. Health Implications of Perchlorate Ingestion; National Academies Press: Washington, DC, 2005.
• U.S. EPA. National Primary Drinking Water Regulations: Cyanide (40 CFR 141.62), 2001.
• U.S. EPA Method 335.1, Determination of Cyanide by Spectrophotometry; EPA: Cincinnati, OH, 2005.
• U.S. EPA Method 335.2, Cyanide by Microdistillation and Titration; EPA: Cincinnati, OH, 2002.
• U.S. EPA Method 335.3, Cyanide by Colorimetry; EPA: Cincinnati, OH, 2002.
• Standard Methods SM-4500-CN-F; American Public Health Association, 1998.
• Bracey, P. R.; Read, R. J.; Savage, R. J. Anal. Chim. Acta 2002, 468, 39–45.
• Wang, J. Anal. Chim. Acta 1999, 381, 1–14.
• Dionex Application Update 148, Determination of Perchlorate in Drinking Water; Sunnyvale, CA, 2004.