Speciation analysis of urine iodine by ion-pair reversed-phase liquid chromatography and inductively coupled plasma mass spectrometry

Abstract

This work described the utilization of ion-pair reversed phase liquid chromatography coupled to inductively coupled plasma mass spectrometry (RP-LC-ICP-MS) for iodine speciation analysis in urine. Considering the requirements of green analytical chemistry and the Ar ICP-MS instrument, three aqueous mobile phases were employed for the separation of seven iodine species including iodide, iodate and five iodo amino acids (monoiodotyrosine – MIT, di-iodotyrosine – DIT, tri-iodothyronine – T₃, reversed tri-iodothyronine – rT₃, and thyroxine – T₄). The aqueous mobile phases were composed of an ion-pair reagent (tetrabutylammonium hydroxide – TBAH) and an eluent (ammonium chloride, L-phenylalanine or deoxycholic acid) at low concentrations in ultrapure water. Owing to tremendous difference in retention behavior between these iodinated forms, a gradient elution mode was performed for the rapid separation of IO₃⁻ and I⁻, MIT and DIT, and T₃, rT₃ and T₄, respectively. Iodine species separation was achieved with a 12.5 mm C₁₈ guard column in 7 min. The detection limits for IO₃⁻, I⁻, MIT, DIT, T₃, rT₃ and T₄ were 0.047, 0.046, 0.057, 0.072, 0.093, 0.094 and 0.081 μg L⁻¹, respectively. Application of the proposed method was demonstrated by the speciation analysis of iodine in four real urine samples. The developed method offered satisfactory recoveries in the 93–106% range and good repeatability, showing great potential in routine analysis of iodine speciation in environmental, food and biological samples.