Three batches of dried kelp (Laminaria japonica Aresch, pur-chased from local market) were used to validate the reliability of the method. The dried kelps (0.300 g) were firstly burned toash for 45 min, in which the iodine is present as iodide. Then, the iodide was dissolved out of the residue by boiling water. The fil-tered iodide solutions (250.00 mL) were prepared as samples anddiluted 10-fold for colorimetric detection by standard additions method. The results shown in Table S2 indicate that the detectionof extracted iodide solutions had a recovery of 94.0–113.4% with RSD of 3.42–5.78%. The average content of iodide in the dried kelp is 0.516 mg g−1.