Method of determination organic iodine (iodotyrosines) in food

It is important to control the substances of the synthesis of biologically active supplements, based on organic forms of iodine (iodotyrosines). But it is no less important to control the content of iodotyrosines in foods. The developed method is sensitive and selective and can determine iodotyrosines with a lower limit of detection (1 ppb). Iodotyrosines have been determined by HPLC-MS/MS. The article contains parameters for chromatographic separation of 3-iodo-L-tyrosine and 3.5-diiodo-L-tyrosine and parameters of the electrospray ionization (ESI) mass spectrometry, describes the methodology of sample preparation and solid phase extraction. The article substantiates the use of mass spectrometry as the most sensitive and selective method for determining the organic iodine as compared to HPLC with UV detection. The enzymatic hydrolysis with proteolytic enzymes has been used for sample preparation in iodothyronine analyses. Solid phase extraction was performed using C18 cartridge. For HPLC-MS/MS analysis iodothyronine derivatives were obtained with a mixture of butanol-acetyl chloride. Degree of iodotyrosine extraction from the matrix of the foodstuffs was not less than 85%, the correlation coefficient of the calibration curve in the concentration range of 1-2000 ng/mL was 0.999, reliable determination of iodine content in foods in the range from 10 to 20 000 mcg/kg.