Trace analysis of iodide in sodium chloride applying amperometric detection

Importance of the Topic

Trace-level determination of iodide in sodium chloride is essential for quality control of salt products and nutritional monitoring. The presence of iodide at µg/kg levels influences regulatory compliance and consumer health benefits. The combination of ion chromatography with amperometric detection offers heightened sensitivity and selectivity compared to conventional detectors.

Objectives and Study Overview

This study aims to establish a robust method for quantifying trace iodide in pure sodium chloride using ion chromatography coupled with amperometric detection. Key goals include achieving low limits of quantification and reliable recoveries in fortified samples.

Methodology

Sample Preparation
20 g of sodium chloride was dissolved in ultrapure water and diluted to 1 L.

Chromatographic Conditions

• Column: Metrosep A Supp 5 – 250/4.0 with Metrosep A Supp 5 Guard/4.0
• Eluent: 6.4 mmol/L sodium carbonate and 2.0 mmol/L sodium hydrogen carbonate
• Flow rate: 0.8 mL/min, Injection volume: 50 µL
• Column temperature: 40 °C, Analysis time: 20 min

Used Instrumentation

• 930 Compact IC Flex Oven/Degasser
• IC Amperometric Detector with wall-jet cell
• 858 Professional Sample Processor
• Ag working electrode, Ag/AgCl reference electrode

Main Results and Discussion

• Measured iodide concentration in solution: 1.55 µg/L with 4.2% RSD (n=3)
• Calculated sample concentration: 77.5 µg/kg
• Spike recoveries: 104.1% and 104.8% at 6.75 µg/L and 12.03 µg/L levels

These findings confirm the method’s precision, accuracy, and strong sensitivity for trace iodide analysis.

Benefits and Practical Applications

• Reliable quality control for salt and related products
• Compliance with nutritional fortification regulations
• Applicability in food safety and environmental monitoring

Future Trends and Applications

The use of shorter columns may further lower quantification limits. Advances in miniaturized IC systems and integration with online monitoring tools are anticipated. Combining amperometric detection with complementary detectors could expand analyte coverage.

Conclusion

The developed IC–amperometric method delivers sensitive and selective detection of iodide at trace levels in sodium chloride. Its robustness, low LOQ, and high recovery make it suitable for routine quality assurance and research applications.

Reference

Metrohm IC Application Note N–73 Version 1