Direct determination of cyanide in drinking water by ion chromatography with pulsed amperometric detection

Importance of the Topic

Free cyanide is a potent toxin with strict regulatory limits in drinking water due to its natural occurrence in foods and release from industrial and mining activities. Rapid and accurate measurement of free cyanide is essential for public health protection and compliance with EPA and FDA standards.

Objectives and Study Overview

This study presents a direct ion chromatography method with pulsed amperometric detection (IC-PAD) optimized for free cyanide in drinking water. The aims were to avoid time-consuming distillation, minimize interferences, and achieve low detection limits compatible with regulated levels.

Methodology and Equipment

An ICS-3000 IC system with a Dionex AS15 analytical column and guard was used. Eluents consisted of degassed deionized water and 200 mM NaOH mixed to deliver 63 mM NaOH. A three-step PAD waveform cleaned and measured cyanide at a -0.10 V detection potential. A pH-Ag/AgCl reference and disposable silver working electrode provided stable responses. Metal interferences were removed on-line using Dionex OnGuard II H cation-exchange cartridges.

Main Results and Discussion

• Linearity was excellent from 2 µg/L to 100 µg/L (r²>0.999). Method detection limit was 1 µg/L.
• Retention time repeatability was 5.78 ± 0.03 min; peak area RSD<1.5% over 62 h of injection.
• Bromide, iodide, sulfite, thiocyanate and thiosulfate showed negligible bias (<±10%).
• Dissolved Fe, Cu, and Ni caused cyanide loss but were effectively removed (>90% recovery) by OnGuard II H cartridges.
• Spike recoveries in treated municipal and surface waters ranged from 80% to 100% for 5 µg/L and 10 µg/L levels, with sample stability over 31 h.

Benefits and Practical Applications

• A direct IC-PAD approach eliminates distillation and sample neutralization steps, reducing analysis time.
• High selectivity and sensitivity support regulatory compliance and routine monitoring.
• Disposable silver electrodes simplify maintenance and ensure reproducible performance.
• On-line metal removal improves accuracy in complex matrices without manual pretreatment.

Future Trends and Potential Applications

• Integration of automated sample pretreatment with IC for high-throughput monitoring.
• Development of miniaturized, field-deployable IC-PAD systems for on-site analysis.
• Coupling with mass spectrometry for speciation of cyanide complexes.
• Improved electrode materials to extend disposable sensor lifetimes.

Conclusion

The optimized IC-PAD method using disposable silver electrodes and on-line metal removal offers a robust, rapid, and sensitive solution for direct free cyanide determination in drinking and surface waters, meeting regulatory requirements and simplifying laboratory workflows.

Instrumental Setup

• Thermo Scientific Dionex ICS-3000 with Single/Dual Gradient Pump and GM-4 degasser
• Dionex IonPac AS15 analytical column (2 × 250 mm) with AG15 guard
• Electrochemical Detector ED (P/N 079830) with pH-Ag/AgCl reference AAA-061756 and disposable Ag working electrode P/N 063003
• Dionex OnGuard II H cartridges (P/N 057086) for metal removal
• Chromeleon 6.7 chromatography data system

References

• EPA Methods 335.1, 335.2, 335.3 for cyanide analysis
• Standard Methods SM-4500-CN-F for ion-selective electrode detection
• Heckenberg et al., J. Chromatogr. A 2004, 1023, 105–112
• Liang et al., J. Chromatogr. A 2005, 1085, 37–41