Analysis of iodine and its species in animal tissues

Abstract

A method allowing the determination of the total iodine content and iodine species in samples of animal tissues using inductively coupled plasma mass spectrometry (ICP-MS) as an element-specific detector was developed. The total iodine content was determined after microwave digestion with 25% (w/w) water solution of tetramethylammonium hydroxide. The detection limit was 26.9 μg kg−1 I, and the accuracy of the determination was proven through the analysis of SRM “Non-Fat Milk Powder,” porcine liver, and Atlantic Cod muscle samples using standard addition methods. The extracts for the speciation analysis were prepared through sample dispersion in water using an Ultra-Turrax® T10. The extraction yields ranged from 46 to 84% for different types of tissues. The determination of the inorganic iodine species was performed using ion-exchange chromatography (PRP X100, mobile phase 100 mmol L−1 ammonium nitrate, pH 7.4) coupled to ICP-MS. A detection limit of 1.1 μg kg−1 I was obtained for both species. The organic iodine species were separated using size-exclusion chromatography (Superdex 75 column, mobile phase 20 mmol L−1 Tris–HCl, pH 7.5) and also detected using ICP-MS. Samples of porcine muscle, liver, kidney and thyroid gland, chicken muscle and liver and Atlantic Cod muscle were analyzed. The porcine thyroid gland and Atlantic Cod muscle samples were the richest in iodine (a more than 10× greater content of iodine than the other samples). With respect to the inorganic species, only iodide was found in the sample extracts. Conversely, many organic iodine species were found in the extracts.