Keywords: دیاکتیل مونوکسیم; Stable isotope; Guanidino group; Ureido group; Liquid chromatography-mass spectrometry; Benzylic rearrangement; Thyroid tissue; BRSIL; benzylic rearrangement stable isotope labeling; GCs and UCs; guanidino and ureido compounds; LC; liquid chromatography;