Analysis of Cyanide Ion and Cyanogen Chloride in Mineral Water by Ion Chromatograph-Post Column Method

Significance of the Topic

The presence of cyanide ion and cyanogen chloride in mineral water poses a potential health risk. Regulatory bodies such as the Japanese Ministry of Health, Labour and Welfare and the CODEX Alimentarius have set strict limits for these analytes to ensure consumer safety. Rapid, reliable analytical methods are essential for routine quality control and compliance testing in the beverage industry.

Objectives and Overview

This study demonstrates an ion chromatography method with post-column derivatization for simultaneous determination of cyanide ion and cyanogen chloride in mineral water. The procedure follows the Japanese Soft Drinks Test Method (MHLW notification Shokuan 1222 No. 4) and aligns with CODEX standards. The goal is to achieve accurate quantification at trace levels (down to 0.001 mg/L) across samples of varying hardness.

Methodology

An ion exclusion mode separation was performed using a sodium tartrate buffer mobile phase. Post-column derivatization consists of two successive reactions: chlorination with chloramine T and coloring with a 1-phenyl-3-methyl-5-pyrazolone/4-pyridinecarboxylate reagent. Detection occurs at 638 nm via UV-VIS absorbance. Sample vials were kept at 4 °C to prevent volatilization of cyanogen chloride.

• Separation column: Shim-pack Amino-Na (100×6 mm, 5 µm) with CN guard column
• Mobile phase: 10 mmol/L sodium tartrate, flow rate 0.6 mL/min, column temperature 40 °C
• Post-column reagents: chloramine T in phosphate buffer (0.5 mL/min, 40 °C), and color reagent mix (0.5 mL/min, 100 °C)
• Injection volume: 100 µL, detection at 638 nm

Instrumentation Used

The analysis was carried out on a Shimadzu Nexera cyanic analysis system equipped with:

• Degassing unit and solvent delivery pumps
• Cooled autosampler (4 °C) to maintain sample integrity
• Column oven set at 40 °C
• UV-VIS detector with a tungsten lamp

Main Results and Discussion

Calibration curves for both analytes were linear over 0.0025–0.025 mg/L, with r2 values ≥0.999. Repeatability tests at 0.0025 mg/L yielded RSDs of 0.26% for cyanide and 0.55% for cyanogen chloride. Spike-and-recovery experiments in three mineral waters of different hardness (10–1468 mg/L as CaCO3) returned recoveries between 97 and 102%, demonstrating method robustness across matrix variations.

Benefits and Practical Applications

This method provides a sensitive, precise, and regulatory-compliant protocol for routine monitoring of cyanide species in bottled water. Its high throughput and stable performance make it suitable for QA/QC laboratories in the beverage industry and public health agencies.

Future Trends and Potential Applications

Advances may include coupling with mass spectrometric detection for enhanced specificity, miniaturized flow cells for lower reagent consumption, and on-site portable systems for rapid field screening. Expansion of the approach to other toxic ions could further broaden its utility.

Conclusion

The described ion chromatography method with post-column derivatization achieves low detection limits, excellent linearity, and reproducibility for cyanide ion and cyanogen chloride in mineral water. It meets stringent regulatory requirements and offers practical advantages for routine water safety testing.

References

• Mineral Water Association of Japan. Transition of Per-Capita Consumption of Mineral Water (2020).
• Ministry of Health, Labour and Welfare. Notification Shokuan 1222 No. 1, Partial amendment to compositional standards (2014).
• CODEX Standard for Natural Mineral Waters: CXS 108-1981, amended 2019.
• Ministry of Health, Labour and Welfare. Notification Shokuan 1222 No. 4, Test Methods for Soft Drinks (2014).