Determination of Essential Elements in Thyroid Samples by Inductively Coupled Plasma Mass Spectrometry and Optical Emission Spectrometry after Tetramethylammonium Hydroxide Solubilization

Abstract

Concentrations of Bromine, Calcium, Copper, Iodine, Iron, Magnesium, manganese, Phosphorus, Selenium, Sulfur, and Cinc in thyroid samples were simultaneously determined by using a modification of the US Food and Drug Administration method for iodine determination. A total of forty-six pieces of total thyroidectomy from different non-tumoral disorders (Goiter -diffuse or nodular-, and autoimmune thyroid diseases -Graves’ disease or Hashimoto thyroiditis) were analyzed. Among them, fifteen had incidental microscopic carcinoma. Analyses were performed by Inductively Coupled Plasma Mass Spectrometry and Inductively Coupled Plasma Optical Emission Spectrometry after TMAH tissue solubilization and matrix modification by addition of a chelating agent, a surfactant, and a matrix modifier. Accuracy and precision of the method were high, according to the analysis on the certified reference materials SRM-1549, ERM-BB422, ERM-CE278k and NRCC-DORM-3. Descriptive, unpaired t-test, statistical, and univariate correlation analyses were performed on results using GraphPad Prism. No statistical differences in element contents were found when considering groups by sex, Goiter type, or kind of autoimmune disorder. Element concentrations in thyroid tissues were significantly different between goiter versus autoimmune disease samples. In particular, goiter samples showed higher contents of Iodine, Selenium, Zinc, Calcium, and Sulfur, and lower contents of Phosphorus and Manganese. A very highly significant direct correlation was obtained for Mg-P in non-cancerigenous goiter samples, non-cancerigenous autoimmune thyroid diseases, and thyroid cancer log-transformed groups (r = 0.83-0.96, p < 0.001). Non-cancerigenous goiter samples showed a significant direct positive correlation for I-Se (r = 0.74). Cancerigenous tissues showed, on average, lower Zn and Mg contents than benign tissues (×0.71 and ×0.85, respectively). Results reflect different elements’ imbalances (I, Se, Zn, Ca, P, Mn, and S) related to thyroid dysfunctions -mostly due to autoimmune diseases.