PROCEDURE FOR CONTENT UNIFORMITY
Accurately weigh 1.69 g of potassium iodate, and transfer to a 1-liter volumetric flask. Dissolve in about 200 mL of water, dilute with water to volume, and mix. This is a stock solution having a concentration of about 1 mg per mL with respect to iodine. Pipet 8 mL of the stock solution into a 250-mL volumetric flask, dilute with water to volume, and mix. Transfer an appropriate aliquot, based on dosage being analyzed (i.e., ¼ gr, 1 mL; ½ gr, 2 mL; 1 gr, 4 mL; 1½ gr, 6 mL; 2 gr, 8 mL; 2½ gr, 10 mL; 3 gr, 12 mL; 4 gr, 16 mL; 5 gr, 20 mL), to a 100-mL volumetric flask containing 8 g of potassium carbonate dissolved in 70 mL of water. Add 1 mL of bromine TS, mix, add sufficient sodium sulfite (about 20 mg) until the solution becomes colorless, and mix. Dilute with water to volume, and mix.
Crush 1 Tablet in a porcelain crucible with a glass rod. Remove any sample adhering to the glass rod with a spatula, and add it to the crucible. Add 4 g of anhydrous potassium carbonate, mix carefully, and gently tap the crucible several times to compact the mixture. Overlay with 4 g more of anhydrous potassium carbonate, and again compact the material thoroughly by tapping. Place the crucible in a preheated muffle furnace, and ignite at 675
for 25 minutes. Cool, add 30 mL of water, carefully heat on a hot plate to dissolve the residue, and filter through a funnel with a glass wool plug into a 100-mL volumetric flask. Repeat the heating and filtration with two additional 30-mL portions of water, and add these filtrates to the volumetric flask. Add 1 mL of bromine TS, mix, add sufficient sodium sulfite (about 20 mg) until the solution becomes colorless, and mix. Dilute with water to volume, and mix.
Prepare a reagent blank by putting 8 g of anhydrous potassium carbonate into a 100-mL volumetric flask and dissolving it in 70 mL of water, add 1 mL of freshly prepared bromine TS, mix, add sufficient sodium sulfite (about 20 mg) until the solution becomes colorless, dilute with water to volume, and mix to obtain the Blank solution.
Transfer 10 mL of the Test solution
to a dry polarographic cell. Bubble nitrogen through the solution for 5 minutes, and then direct the stream of nitrogen above the solution. Use a suitable differential pulse polarograph equipped with a saturated calomel reference electrode and a dropping mercury electrode with a 1-second drop time. Scan from
1.5V at the rate of 5 mV per second, and 50-mV pulses. Record the polarogram of the Test solution
, the Standard solution
, and the Blank solution.
At the peaks near
1.18V in the polarograms obtained from the Standard solution
and the Test solution
measure the heights from the baseline, as established by the Blank solution.
Calculate the amount of iodine, in µg, in the Tablet taken by the formula:
(126.90 / 214.00)(54.08V)(PHU / PHS),
in which 126.90 and 214.00 are the atomic weight of iodine (I) and the molecular weight of potassium iodate (KIO3
), respectively; V
is the volume, in mL, of the aliquot portion of potassium iodate solution used to prepare the Standard Solution;
are the peak heights obtained from the Test solution
and the Standard solution
, respectively. Proceed as directed for Content Uniformity 905
, using the results obtained by this procedure to determine the total iodine content of individual Tablets, and use the Assay preparation
to perform the composite determination for iodine. The requirement is met if the amount of iodine in each Tablet is within the range of 85.0% to 115% of the composite assay for iodine with a relative standard deviation of not more than 6.0%.