Total Iodine Quantification in Fluids and Tissues from Iodine- or Iodide-Supplemented Rats by Ion Chromatography Following Microwave-Assisted Digestion

Abstract

Background:

Iodine is a crucial component of thyroid hormones, and several reports have shown that iodine per se is implicated in the physiopathology of other organs.

Methods:

Innovative ion chromatography detection following a four-step temperature ramp microwave digestion in 25–50 mM nitric acid was developed to measure total iodine in biological fluids and tissue samples from female Sprague-Dawley rats supplemented with 0.05% molecular iodine (I₂) or 0.05% potassium iodide (I⁻) in drinking water.

Results:

The reported method allows the measurement of total iodine with a limit of quantification of 13.7 μg L⁻¹, recoveries of 96.3–100.3%, and intra- and inter-assay variations, of 3.5% and 7.4% respectively. Analysis of biological fluids showed that after 48 hours, iodine-supplemented animals exhibited significantly higher levels of total iodine in both serum and urine compared with those supplemented with iodide. The half-life of iodine in serum and urine measured over the first 48 h showed similar patterns for both the I₂ (7.89 and 7.76 hours) and I⁻ (8.27 and 8.90 hours) supplements. Differential uptake patterns were observed in tissues after 6 days of supplements, with I⁻ preferentially retained by thyroid, lactating mammary gland, and milk, and a slightly but significantly higher capture of I₂ in pituitary, ovary, and virgin mammary gland.

Conclusions:

We developed a rapid, selective, and accurate digestion method to process fluid and tissue samples that permits reproducible measurements of total iodine by ion chromatography; iodine or iodide supplement show a similar serum and urine half-life, but organ-specific uptake depends on the chemical form of the iodine supplement.