Iodide Assay by Ion Chromatography

Importance of the Topic

Potassium iodide is a critical agent for thyroid protection and overactive thyroid treatment, and its accurate quantification is essential for pharmaceutical quality control. Traditional manual titration methods often suffer from poor precision and accuracy. Implementing a selective ion chromatography assay ensures reliable measurement of iodide content and strengthens analytical rigor in compliance with pharmacopeial standards.

Objectives and Study Overview

This study aimed to develop and validate a rapid, sensitive ion chromatography method for both assay and identification of iodide in potassium iodide. The method supports USP monograph modernization by offering a precise alternative to manual titration and integrates identification and quantification into a single protocol.

Methodology

The assay employed an anion‐exchange column (Metrosep A Supp 17 – 100/4.0 mm, L91 packing) with suppressed conductivity detection. Key chromatographic conditions included a 10 mM sodium carbonate eluent, flow rate of 1.0 mL/min, column temperature at 45 °C, and injection volume of 20 µL. Validation parameters covered specificity, linearity (3.0–22.5 mg/L iodide), accuracy, precision, solution stability, system suitability, and intermediate precision according to USP <1225> criteria.

Instrumentation

• Metrohm 940 Professional IC Vario
• Metrosep A Supp 17 – 100/4.0 mm column (L91 packing)
• Suppressed conductivity detector

Main Results and Discussion

• Specificity: No co‐elution or interference; resolution between iodide and nearest peak ≥ 2.0.
• Linearity: Concentration range 3.0–22.5 mg/L; correlation coefficient 0.9999; y-intercept bias 0.73%.
• Accuracy and Precision: Average assay recovery between 98.9% and 100.6%; RSD ≤ 0.86%.
• Solution Stability: Peak area change ≤ 0.77% over the tested period.
• System Suitability: Tailing factor ≤ 1.75, resolution ≥ 6.5, repeatability RSD ≤ 0.41%.

The validation results met all USP acceptance criteria, demonstrating that the IC method is a robust and selective approach for iodide assay and identification in pharmaceutical potassium iodide.

Benefits and Practical Applications

• Combines identification and quantification in one chromatographic run, streamlining QA/QC workflows.
• Improves precision and accuracy compared to manual titration.
• Enables simultaneous monitoring of other anionic impurities such as chloride and sulfate.
• Applicable to various over-the-counter potassium iodide formulations, including oral solutions and tablets.

Future Trends and Opportunities

Advancements may include integration with automated sample handling, miniaturized columns for faster analysis, and coupling with mass spectrometry to enhance selectivity. Expanding the method to other protective agents against radioactive exposure could further broaden its pharmaceutical applications.

Conclusion

A single ion chromatography procedure for the identification and assay of iodide in potassium iodide was successfully developed and validated. The method fulfills USP criteria, offers superior accuracy and precision over manual titration, and simplifies routine pharmaceutical analysis.

References

• Metrohm USA, Inc.
• United States Pharmacopeia