Analysis of thyroid hormones in health foods by LC/MS

Abstract

A method was developed for analysis of thyroid hormones, 3,5,3′-triiodo-L-thyronine (T3) and L-thyroxine (T4), in health foods by liquid chromatography-electrospray ionization-mass spectrometry (LC/ESI-MS). In order to release T3 and T4 from thyroglobulin, samples were first hydrolyzed enzymatically using protease at a temperature of 37±1°C for 28 h. The T3 and T4 were extracted with ethyl acetate and then the ethyl acetate layer was evaporated. The residue was dissolved in the mobile phase and analyzed by LC/MS. The LC separation was carried out on a ODS-3 column (2.1 x 150 mm) using H2O/CH3CN/CH3COOH (650/350/5) as the mobile phase. LC/ESI-MS was performed in the selected ion monitoring (SIM) mode using [M + H]+ ions at m/z 652 for T3 and m/z 778 for T4. The detection limit of both T3 and T4 released from thyroglobulin was 0.1 μg/g in health foods. The present method was applied to analysis of three health foods which were labeled as foods for dieting. T3 and T4 were detected in two of the samples, and their contents were 16 and 29 μg/g and 31 and 90 μg/g, respectively.