Determination of thyroid hormones and their metabolites in tissue using SPE UPLC-tandem MS

A solid-phase liquid chromatography tandem mass spectrometry (SPE LC-MS/MS) method was developed to determine thyroid hormones and their metabolites in tissue samples. The separation was achieved using reversed-phase ultra-performance liquid chromatography (UPLC); the mass spectrometric detection was achieved by positive electrospray ionization and multiple reaction monitoring. Prior to the UPLC separation a sample cleanup with a cation exchange was performed. ¹³C₆ labeled internal standards were used for the thyroid hormones and their metabolites. The method was linear over a range from 0.23 to 90 nmol/L for thyroxine and from 0.23 to 9 nmol/L for the metabolites. The lower limit of quantification ranged from 0.98 to 1.73 pg on column. Intra- and total assay variation were <10 and <15%, respectively. This method enables us to link thyroid hormone tissue concentrations to local iodothyronine deiodinase expressions, which will enhance our understanding of the regulation of thyroid hormone metabolism on the tissue level.