Povidone-iodine Pharmacopoeia Standard

Main active ingredients
Complex of 1-vinyl-2-pyrrolidone homopolymer and iodine. Calculated on a dry basis, the available iodine (I) content should be 9.0% to 12.0%. 
Traits
Yellow-brown to red-brown amorphous powder. Soluble in water or ethanol, insoluble in ether or chloroform. [1]
identify
Take about 0.5g of this product, add 5mL of water to dissolve, and then test according to the following method.
(1) Take 1 drop of the solution, add 9 ml of water and 1 ml of starch indicator solution, and it will appear dark blue.
(2) Take 0.5 mL of the solution, apply it on a glass plate with an area of approximately 7.5 cm × 2.6 cm, and place it at room temperature with low humidity overnight to dry to form a brown, dry film that is easily soluble in water. [1]
examine
Loss on drying
Take about 5g of this product, weigh it accurately, dry it at 105°C for 4 hours, weigh it, and weigh it after continuing to dry for 1 hour each time until the weight difference after two consecutive dryings does not exceed 5.0mg; lose weight Must not exceed 8.0%.
Residue on ignition
Take 1.0g of this product and check it in accordance with the law. The remaining residue should not exceed 0.1%.
heavy metal
Take the residue left under the ignition residue category and inspect it in accordance with the law. The heavy metal content must not exceed 20 parts per million.
Arsenic salt
Take 1.3g of this product, add 0.5g of calcium hydroxide, mix well, add an appropriate amount of water (about 2mL), stir evenly, after drying, first burn it with a small fire to carbonize, then burn it at 600℃ to completely ashes, and let it cool. , add 5mL of hydrochloric acid and 23mL of water, check according to law, and it should comply with regulations (0.00015%).
Nitrogen content
Take about 0.50g of this product, weigh it accurately, and measure it according to the nitrogen determination method. Calculated on a dry basis, the nitrogen content should be 9.5% to 11.5%.
iodide ion
Take about 0.50g of this product, weigh it accurately, place it in a 250mL Erlenmeyer flask, add 100mL of water to dissolve, add a few drops of sodium bisulfite test solution to make the color of the solution disappear, add 10mL of nitric acid, and accurately add silver nitrate titrant (0.1 mol/L) 25mL, shake well, add 0.5mL of ferric ammonium sulfate indicator solution, titrate with ammonium thiocyanate titrant (0.1mol/L) until the solution shows light brick red, and correct the titration result with a blank test. Each 1mL of silver nitrate titrant (0.1mol/L) is equivalent to 12.69mg of I. Calculate the percentage of total iodine minus the percentage of available iodine under the content determination item to obtain the percentage of iodide ions. Calculated as dry product, the iodide ion content shall not exceed 6.6%. 
Content determination
Take about 1g of this product, weigh it accurately, put it in a beaker, add 120mL of water, stir to dissolve, and titrate with sodium thiosulfate titrant (0.1mol/L) according to the potentiometric titration method (2010 edition of the Pharmacopoeia, Appendix VII A) , each 1mL of sodium thiosulfate titrant (0.1mol/L) is equivalent to 12.69mg of I.