Iodine speciation in dog foods and treats by high performance liquid chromatography with inductively coupled plasma mass spectrometry detection.

ABSTRACT

An analytical method for determination of the iodine species 3-monoiodotyrosine (MIT), iodide, 3,5-diiodotyrosine (DIT), 3,5-diiodothyronine (3, 5-T2), 3,5,3'-triiodothyronine (T3), and thyroxine (T4) in dog foods and treats is reported. Iodine speciation was carried out using a HPLC method capable of both anion-exchange and reversed-phase retention coupled with inductively coupled plasma mass spectrometry detection (LC-ICP-MS). The method was evaluated by the analysis of the iodine species concentrations in twelve dog foods and treats following enzymatic digestion. The concentrations of MIT, iodide, DIT, T3, and T4 in the samples ranged from 0.64-59.5µg/g, 0.86-4.05µg/g, iodide, DIT, T2, T3, and T4 were 97%, 114%, 89%, 102%, 90%, and 80%, respectively. An additional analysis was done for DIT, T3, and T4 in the enzyme digest by LC-triple-quadrupole mass spectrometry (LC-MS/MS) to cross-validate the results obtained by LC-ICP-MS. Both methods were in good agreement for the concentrations of DIT, T3, and T4.