Packaging and storage—
Preserve in tight containers.
Identification—
A:
The UV absorption spectrum of a 1 in 10,000 solution in dilute hydrochloric acid (1 in 50) in 80 percent alcohol exhibits maxima at the same wavelengths as that of a similar solution of
USP Liothyronine RS, concomitantly measured; and the respective absorptivities, both calculated on the dried basis in terms of the acid, at the wavelength of maximum absorbance at about 297 nm, do not differ by more than 5.0%.
B:
Heat about 50 mg with a few drops of sulfuric acid in a porcelain crucible: violet vapors of iodine are evolved.
C:
The residue from the ignition of it responds to the tests for
Sodium 
191
.
Specific rotation 781S:
between +18
and +22
.
Test solution:
20 mg per mL, in a mixture of alcohol and 1.2 N hydrochloric acid (4:1).
Limit of inorganic iodide—
Extracting solution, Reference solution, and Electrode system—
Proceed as directed in the
Limit of inorganic iodide test under
Levothyroxine Sodium.
Test solution—
Transfer 7.5 mg of Liothyronine Sodium to a beaker, add 100 mL of Extracting solution, and sonicate for 5 minutes.
Procedure—
Proceed as directed in the
Limit of inorganic iodide test under
Levothyroxine Sodium: the limit is 0.08%.
Limit of levothyroxine sodium—
Mobile phase and Chromatographic system—
Proceed as directed in the Assay.
Standard solution—
Proceed as directed for Standard preparation in the Assay.
Test solution—
Proceed as directed for Assay preparation in the Assay.
Procedure—
Separately inject equal volumes (about 100 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure the levothyroxine peak responses. Calculate the quantity, in µg, of levothyroxine sodium (C
15H
10I
4NNaO
4) in the portion of Liothyronine Sodium taken by the formula:
(798.85/776.87)(10C)(rU / rS),
in which 798.85 and 776.87 are the molecular weights of levothyroxine sodium and levothyroxine, respectively;
C is the concentration, in µg per mL, of
USP Levothyroxine RS in the
Standard solution; and
rU and
rS are the levothyroxine peak responses obtained from the
Test solution and the
Standard solution, respectively: not more than 5.0% of levothyroxine sodium is found.
Chloride content—
Weigh accurately 100 mg, previously dried, and transfer to a platinum dish. Ignite over a low flame, protecting the dish from air currents during the ignition. When carbonization is complete, cool the dish, add 2 drops of water, and break up the charred mass thoroughly with a stirring rod. Add 10 mL of water and 5 mL of ammonium hydroxide, and mix. Transfer the slurry to a glass-stoppered, 50-mL flask, and wash the platinum dish and the stirring rod with water, adding the washings to the flask, until the volume of the solution is about 25 mL. Add 10 mL of silver nitrate solution (1 in 20), shake thoroughly, and filter through a retentive paper into a 50-mL color-comparison tube. Wash the flask and the filter paper with 10 mL of water, and add the washings to the tube. Acidify the combined filtrate and washings to litmus with nitric acid, and dilute with water to 50 mL. Prepare a control by mixing 5 mL of ammonium hydroxide, 20 mL of water, and 10 mL of silver nitrate solution (1 in 20), filtering the mixture through a retentive paper into a 50-mL color-comparison tube, then washing the filter paper with 10 mL of water into the tube, acidifying the contents of the tube to litmus with nitric acid, diluting with water to 50 mL, and adding sodium chloride solution (1 in 1000) in 0.1-mL increments until the turbidity of the control matches that of the test solution. Not more than 2.0 mL of sodium chloride is required (1.2%).
Sodium content—
Weigh accurately about 100 mg, previously dried, and transfer to a platinum dish. Add 8 to 10 drops of sulfuric acid, and ignite to constant weight, taking care to avoid spattering. Each mg of residue is equivalent to 0.324 mg of Na. Correct the result for the amount of sodium equivalent to the NaCl found in the test for Chloride content: not less than 2.9% and not more than 4.0% is found.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of water and acetonitrile (60:40) that contains 0.5 mL of phosphoric acid in each 1000 mL. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
0.01 M Methanolic sodium hydroxide—
Dissolve 400 mg of sodium hydroxide in 500 mL of water. Cool, add 500 mL of methanol, and mix.
Liothyronine stock solution—
Dissolve an accurately weighed quantity of
USP Liothyronine RS in
0.01 M Methanolic sodium hydroxide to obtain a solution having a known concentration of about 0.4 mg of liothyronine per mL.
Levothyroxine stock solution—
Dissolve an accurately weighed quantity of
USP Levothyroxine RS in
0.01 M Methanolic sodium hydroxide to obtain a solution having a known concentration of about 0.4 mg of levothyroxine per mL. Make a 1:100 dilution of this solution using
Mobile phase.
Standard preparation—
Transfer appropriate volumes of Liothyronine stock solution and Levothyroxine stock solution to a suitable container, and dilute quantitatively and stepwise, if necessary, with Mobile phase to obtain a solution having known concentrations of about 10 µg of liothyronine per mL and 0.5 µg of levothyroxine per mL.
Assay preparation—
Transfer an accurately weighed portion of 100 µg of Liothyronine Sodium to a centrifuge tube, add 2 glass beads, pipet 10 mL of Mobile phase into the tube, and mix using a vortex mixer for 3 minutes. Centrifuge to obtain a clear supernatant, filtering if necessary.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 225-nm detector and a 4.6-mm × 25-cm column that contains packing L10. The flow rate is about 1.5 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the resolution,
R, between levothyroxine and liothyronine is not less than 5.0; and the relative standard deviation for replicate injections is not more than 2.0% for liothyronine.
Procedure—
Separately inject equal volumes (about 100 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in µg, of C
15H
11I
3NNaO
4 in the portion of Liothyronine Sodium taken by the formula:
(672.96/650.97)(10C)(rU / rS),
in which 672.96 and 650.97 are the molecular weights of liothyronine sodium and liothyronine, respectively;
C is the concentration, in µg per mL, of
USP Liothyronine RS in the
Standard preparation; and
rU and
rS are the liothyronine peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
;)
