Determination of Liothyronine and Levothyroxine in Dietary Supplements by HPLC Using a Pre-column Derivative

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A new method to identify liothyronine (T3, 3,3,5-triiodo-L-thyronine) and levothyroxine (T4, L-thyroxine), which are thyroid hormones, in dietary supplements by high-performance liquid chromatography was developed using a pre-column derivative with 4-fluoro-7-nitrobenzofurazan (NBD-F), without using liquid chromatography (LC)/MS. T3 and T4 in a dietary supplement were extracted with 10% ammonia water. The extract was treated with a polyvinylpolypyrrolidone (PVPP) column. The T3 and T4 adsorbed on the PVPP were eluted with 60% acetonitrile. T3 and T4 present in the eluate from the PVPP column were then derivatized with NBD-F. The reaction of T3 and T4 with NBD-F was complete after 30 min at 60°C. These derivatives were measured by HPLC using an octadecylsilane (ODS) column with a fluorescent detector. 0.1% Phosphoric acid was added to 630 ml of acetonitrile to a final volume of 1000 ml, and the mixture was used as the mobile phase. The excitation wavelength on the fluorescent detector was 470 nm, and the emission wavelength was 530 nm. The stability of the peak area of T3-NBD and T4-NBD was maintained for 12 hr. The linearity of T3 and T4 as a coefficient of the correlation value was 0.9999, and the quantitation limit of T3 and T4 was 0.002 μg/ml. The results confirmed that T3 and T4 were added to eight dietary supplements. The recovery rate was in the range of 80.4-103.7% for T3 and 79.8-101.5% for T4, and the precisions, as measured by the standard deviation, were within 4.8% and 4.3%, respectively.

Determination of Liothyronine and Levothyroxine in Dietary Supplements by HPLC Using a Pre-column Derivative

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