Determination of total iodine content in edible seaweeds: Application of inductively coupled plasma-atomic emission spectroscopy

Iodine is an essential element necessary for the synthesis of thyroid hormones, and its deficiency is a common problem worldwide. To avoid iodine insufficiency, the intake of this element must be properly evaluated concerning its adequate intake (AI), which is estimated at 90, 150, and 200 μg per day, for children, adults, and pregnant women, respectively. One of the most abundant resources available for iodine is the consumption of edible seaweeds. In this work, ten species of edible seaweeds: one green (Ulva rigida), five red (Chondracanthus teedei var. lusitanicus, Chondrus crispus, Gracilaria gracilis, Grateloupia turuturu, Osmundea pinnatifida), and four brown species (Bifurcaria bifurcata, Fucus vesiculosus, Saccorhiza polyschides, Undaria pinnatifida), collected from the near-pristine Portuguese seashore, were analyzed for iodine content. The iodine concentration was determined by optimized microwave-assisted extraction in aqua regia (AR), followed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis. The method was validated by using the standard reference material (kelp) obtaining a maximum recovery of 100 ± 15%. The studied species contained a wide range of iodine concentrations, ranging from 33 ± 3 μg g⁻¹ dry weight (dw) (U. rigida), up to 302 ± 26 μg g⁻¹ dw (O. pinnatifida), 352 ± 21 μg g⁻¹ dw (F. vesiculosus) and 391 ± 24 μg g⁻¹ dw (B. bifurcata). The results show that the analyzed seaweeds can serve as a beneficial resource for iodine, however, their consumption must be balanced in a way that does not exceed the adequate estimated iodine intake for population groups.