Speciation analysis of iodine in seaweed: optimisation of extraction procedure and chromatographic separation

Rationale. Iodine is an essential element required for human health and metabolism. Seafood and especially seaweed can accumulate iodine to high amounts. Iodine may exist in different chemical forms (species) in seaweeds.
Methodology. The present study describes the development and optimisation of a method for iodine speciation analysis in seaweed based on high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS). The extraction procedure was conducted in two steps, pancreatic enzymatic extraction followed by alkaline extraction with tetramethylammonium hydroxide for optimum extraction efficiency without compromising species integrity.
Results and discussion. Total iodine and iodine species were determined in a range of brown (6 samples), red (6 samples) and green (3 samples) seaweeds. A large variation in the total iodine content of the different seaweeds was observed (33-5611 mu g g(-1) dry weight) with the highest levels encountered in brown seaweed. Iodine speciation analysis revealed differences in the speciation profile of the different types of seaweed. In all seaweeds iodide was the predominant species, and minor contents of MIT (monoiodotyrosine) and DIT (diiodotyrosine) were found in most seaweeds. Furthermore, peaks originating from six unknown iodine-containing species were observed in the chromatograms, especially in red and green seaweeds, while less abundant in brown seaweeds. The speciation method presented here will be valuable in future studies on iodine speciation in seaweed and an important tool for the investigation of iodine speciation and biotransformation in marine algae.