Identification (1) Take about 50mg of this product, put it in a crucible and heat it with a small fire, which will decompose and produce purple iodine vapor. (2) Take about 0.5mg of this product, add water-ethanol-sodium hydroxide test solution-hydrochloric acid (3:2.5: 1: 1) solution and 7.5ml of sodium nitrite test solution 1ml, shake well, leave it in the dark for 20 minutes, and add concentrated ammonia/kloc-0. Check the inorganic phosphorus, accurately weigh an appropriate amount of analytically pure potassium iodide, add water to dissolve it, and make a solution containing 0. 1 3 1 mg per1ml, accurately measure1ml, put it in a 1000 ml volumetric flask, and add sulfuric acid solution (/kloc-0). In addition, accurately weigh 12.5mg of this product, put it in a 100ml volumetric flask, add sulfuric acid solution (1→ 100), dilute it to scale, and shake it well as the test solution. With iodine-iodine ion as indicator electrode and silver-silver chloride as reference electrode, under magnetic stirring, the potentials of reference solution and test solution are measured respectively until the degree is stable and the potential (mV) is recorded. The potential (mV) of test solution should not be lower than that of reference solution (0.08%). Take an appropriate amount of sodium iopromide reference substance which has been dried under reduced pressure at 60℃ for 4h, accurately weigh it, add 0.02mol/L sodium hydroxide solution-methanol (1: 1) solution to dissolve and dilute it, and make a solution containing 10μg per/ml as reference substance solution; Take an appropriate amount of this product, weigh it accurately, dissolve it with the above solution and dilute it to make a solution containing about 0.5mg per 1ml as the test solution. According to the chromatographic conditions under the content determination, accurately measure each 100μl of the above two solutions, inject them into the liquid chromatograph respectively, and record the chromatogram. According to the external standard method, the content of sodium iodide should not exceed 2.0% in terms of peak area. Loss on drying took this product, used phosphorus pentoxide as desiccant, and dried it under reduced pressure at 60℃ for 4 hours. The weight loss shall not exceed 1 1.0% (Appendix VIII L of China Pharmacopoeia 2000). The content was determined by high performance liquid chromatography (Appendix ⅴ D of China Pharmacopoeia 2000). Octadecylsilane bonded silica gel is used as a filler for chromatographic conditions and system suitability test. The mobile phase is methanol-water-phosphoric acid (600: 400:1); The detection wavelength is 225 nm. According to the peak value of L- thyroxine sodium, the theoretical plate number should be no less than 1800, and the peak separation degree of L- thyroxine sodium and iodothyronine sodium should meet the requirements. Determination method: Take this product, accurately weigh it, add 0.02mol/L sodium hydroxide solution-methanol (1: 1) solution to dissolve it, quantitatively dilute it into a solution containing about 5μg per 1ml, accurately measure 50μl, inject it into a liquid chromatograph, and record the chromatogram; Another appropriate amount of levothyroxine sodium reference substance dried at 60℃ for 4 hours was determined by the same method, and the peak area was calculated by external standard method. Thyroid hormone drugs. Store in a cool place, sealed and preserved.