Determination of cyanide in alkaline solutions using ion chromatography

Significance of the topic

Free cyanide is highly toxic and regulated in environmental waters. Ion chromatography with pulsed amperometric detection offers selective, sensitive determination of cyanide in alkaline scrubber solutions, drinking water, and wastewater, with fewer interferences than conventional methods.

Objectives and overview of the study

The aim was to update an existing IC method for quantifying cyanide in alkaline solutions using a Dionex IonPac AS7 column (2 mm) and PAD. The study examined performance in U.S. EPA Method 335.2 (1.25 M NaOH) and 335.4 (0.25 M NaOH) matrices, and demonstrated application to drinking water and wastewater.

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

The method enables direct, interference-free cyanide monitoring in alkaline scrubbers, environmental waters, and industrial effluents. Reduced eluent consumption and waste enhance laboratory efficiency and green credentials.

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

The updated IC-PAD method using a 2 mm IonPac AS7 column provides rapid, sensitive, and accurate cyanide determination in alkaline solutions and environmental samples. Excellent linearity, low MDLs, and robust recoveries support compliance with regulatory requirements and routine monitoring.

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.