Determination of cyanide in alkaline solutions using ion chromatography

Significance of the topic

Objectives and overview of the study

Methodology

• Eluent preparation: 0.5 M sodium acetate, 100 mM NaOH, 0.5% ethylenediamine; degassed and blanketed with inert gas.
• Calibration: Cyanide stock (1000 mg/L) and standards in water, 0.25 N and 1.25 N NaOH over 0.005–2 mg/L.
• Sample prep: Direct injection of alkaline scrubber, simulated samples (cyanide/sulfide), and real water samples diluted 1:1 with 0.5 N NaOH.

Used instrumentation

• Thermo Scientific Dionex ICS-6000 HPIC System with RFIC-EG module and Electrochemical Detector.
• AS-AP Autosampler (250 µL syringe) and Chromeleon CDS v7.2.10.
• Dionex IonPac AS7 analytical column (2×250 mm) with AG7 guard (2×50 mm).
• Electrochemical detection in PAD mode with silver working and Ag/AgCl reference electrodes.

Chromatographic conditions

• Flow rate: 0.25 mL/min; column temp. 30 °C; injection volume 50 µL; run time 20 min.
• PAD waveform: −0.10 V (0–0.90 s), −1.00 V (0.91–0.93 s), −0.30 V (0.93–1.00 s) vs Ag/AgCl.

Main results and discussion

• Cyanide elutes at ~6.8 min, fully resolved from sulfide and oxygen background.
• Quadratic calibration curves (0.005–2 mg/L) with r² ≥ 0.9996 in all matrices.
• Method detection limits: 0.0001 mg/L (water), 0.01 mg/L (0.25 N NaOH), 0.03 mg/L (1.25 N NaOH).
• Spike recoveries: 93–108% across sulfide ratios (1:10 to 1:5) and matrices.
• Real samples: Drinking water and wastewater show no native cyanide; spiked recoveries 96–99%.

Benefits and practical applications

Future trends and possibilities

• Integration with automated sampling for on-line process monitoring.
• Extension to simultaneous detection of other electroactive anions.
• Miniaturized or portable IC-PAD systems for field analysis.
• Advances in electrode materials to lower detection limits further.

Conclusion

Reference

1. U.S. Environmental Protection Agency. Cyanide Compounds; 2016.
2. U.S. EPA. Cyanide Clarification of Free and Total Cyanide Analysis for Safe Drinking Water Act Compliance; 2019.
3. California State Water Resources Control Board. An Overview and Comparison of Methods for Cyanide Analysis; 2014.
4. U.S. EPA. Method 335.4: Determination of Total Cyanide by Semi-Automated Colorimetry; 2006.
5. U.S. EPA. Method 335.2: Cyanide, Total (Titrimetric, Spectrophotometric); 1978.
6. Yang H.; Rohrer J. Application Update 107: Determination of Cyanide in Strongly Alkaline Solutions; Thermo Fisher Scientific; 2003.
7. Yang H.; Rohrer J. Application Note 173: Direct Determination of Cyanide in Drinking Water by Ion Chromatography with PAD; Thermo Fisher Scientific; 2006.
8. Cheng J.; Jandik P.; Avdalovic N. Pulsed Amperometric Detection of Sulfide, Cyanide, Iodide, Thiosulfate, Bromide and Thiocyanate in IC. Anal. Chim. Acta. 2005;536:267–274.
9. Thermo Fisher Scientific. Dionex IonPac AS7 Column Product Manual; 2010.
10. Thermo Fisher Scientific. Technical Note 71: Eluent Preparation for High-Performance Anion-Exchange Chromatography with PAD; 2007.