Determination of total iodine in thyroid tablets with polarography

Importance of the Topic

• Thyroid hormones control metabolism and growth, requiring accurate iodine levels for proper physiological function.
• Quality control in pharmaceutical production of levothyroxine and liothyronine tablets depends on reliable iodine quantification.
• Compliance with pharmacopeial standards ensures patient safety and treatment efficacy.

Objectives and Study Overview

This application note describes an indirect differential pulse polarography method for total iodine determination in synthetic thyroid tablets. Following the United States Pharmacopeia monograph, the procedure converts organically bound iodine to iodate via dry ashing, with subsequent electrochemical quantification.

Methodology and Instrumentation

Sample preparation entails dry ashing of tablet material in a muffle furnace to mineralize organic components and release iodine as iodate. The iodate content is then measured using the 884 Professional VA system in differential pulse mode.

• Working electrode: Multi-Mode Electrode pro operating as a dropping mercury electrode (DME).
• Reference electrode: Ag/AgCl with 3 mol/L KCl bridge electrolyte.
• Auxiliary electrode: Platinum rod.
• Measurement parameters: start potential –0.8 V, end potential –1.5 V, step potential 0.005 V, step time 1 s, pulse amplitude 0.05 V, iodate peak at –1.18 V.

Key Results and Discussion

The method delivered a measured iodine content of 70.59 µg per tablet (92.3% recovery) for unspiked samples and 144.58 µg (101.9% recovery) for tablets spiked with 72.55 µg iodine. Differential pulse polarograms showed well-defined peaks at the expected potential, confirming method specificity and reproducibility in line with USP requirements.

Benefits and Practical Applications

• High accuracy and precision meeting pharmacopeial guidelines.
• Robust sample preparation via dry ashing reduces matrix interferences.
• Versatile 884 Professional VA system supports routine quality control in pharmaceutical laboratories.

Future Trends and Potential Applications

Automation of ashing and integration with flow-through electrochemical systems may increase throughput. Miniaturized and portable polarographic devices could enable on-site testing and expansion to other halogen determinations in environmental and clinical settings.

Conclusion

The indirect differential pulse polarography approach provides a reliable, pharmacopeia-compliant method for total iodine determination in thyroid tablets, ensuring product quality and therapeutic effectiveness.

Reference

1. United States Pharmacopeia. Monograph: Thyroid Tablets.
2. Metrohm. Application Note AN-V-240: Determination of total iodine in thyroid tablets with polarography. Internal reference AW VA CH-0633-042024.