Method name: hypromellose — determination of hydroxypropoxy — determination of hydroxypropoxy
Scope of application: This method uses the hydroxypropoxy determination method to determine the content of hydroxypropoxy in hypromellose.
This method is applicable to hypromellose.
Principle of the method: Calculate the content of hydroxypropoxy in the test product according to the hydroxypropoxy determination method.
Reagent:
1. 30% (g/g) chromium trioxide solution
2. Sodium hydroxide titration solution (0.02mol/L)
3. Phenolphthalein indicator solution
4. Sodium bicarbonate
5. Dilute sulfuric acid
6. Potassium iodide
7. Sodium thiosulfate titration solution (0.02mol/L)
8. Starch indicator solution
equipment:
Sample preparation: 1. Sodium hydroxide titration solution (0.02mol/L)
Preparation: Take 5.6mL of clear saturated sodium hydroxide solution, add freshly boiled cold water to make it 1000mL.
Calibration: Take about 6g of standard potassium hydrogen phthalate dried at 105°C to constant weight, weigh it accurately, add 50mL of freshly boiled cold water, shake to make it dissolve as much as possible; add 2 drops of phenolphthalein indicator solution, use this Liquid titration, when approaching the end point, the potassium hydrogen phthalate should be completely dissolved, and titrated until the solution becomes pink. Every 1mL of sodium hydroxide titration solution (1mol/L) is equivalent to 20.42mg of potassium hydrogen phthalate. Calculate the concentration of this solution based on the consumption of this solution and the amount of potassium hydrogen phthalate taken. Quantitatively dilute 5 times to make the concentration 0.02mol/L.
Storage: Put it in a polyethylene plastic bottle and keep it sealed; there are 2 holes in the plug, and 1 glass tube is inserted into each hole, 1 tube is connected with a soda lime tube, and 1 tube is used for sucking out the liquid.
2. Phenolphthalein indicator solution
Take 1g of phenolphthalein, add 100mL of ethanol to dissolve
3. Sodium thiosulfate titration solution (0.02mol/L)
Preparation: Take 26g of sodium thiosulfate and 0.20g of anhydrous sodium carbonate, add an appropriate amount of freshly boiled cold water to dissolve into 1000mL, shake well, and filter after standing for 1 month.
Calibration: take about 0.15g of standard potassium dichromate dried at 120°C with constant weight, accurately weigh it, put it in an iodine bottle, add 50mL of water to dissolve, add 2.0g of potassium iodide, shake gently to dissolve, add 40mL of dilute sulfuric acid, Shake well and seal tightly; after 10 minutes in a dark place, add 250mL of water to dilute, and when the solution is titrated to near the end point, add 3mL of starch indicator solution, continue titration until the blue color disappears and becomes bright green, and the titration result is used as a blank Trial correction. Every 1mL of sodium thiosulfate (0.1mol/L) is equivalent to 4.903g of potassium dichromate. Calculate the concentration of the solution according to the consumption of the solution and the amount of potassium dichromate taken. Quantitatively dilute 5 times to make the concentration 0.02mol/L.
If the room temperature is above 25°C, the temperature of the reaction solution and dilution water should be cooled to about 20°C.
4. Starch indicator solution
Take 0.5g of soluble starch, add 5mL of water and stir well, then slowly pour into 100mL of boiling water, stir as you add, continue to boil for 2 minutes, let cool, pour out the supernatant, and you get it. This solution should be freshly prepared before use.
Operation steps: Take 0.1g of this product, weigh it accurately, put it in the distillation bottle D, add 10mL of 30% (g/g) cadmium trichloride solution. Fill the steam generating tube B with water to the joint, and connect the distillation unit. Immerse both B and D in an oil bath (it can be glycerin), make the liquid level of the oil bath consistent with the liquid level of the cadmium trichloride solution in the bottle D, turn on the cooling water, and if necessary, let the nitrogen stream flow in and control its flow rate to 1 bubble per second. Within 30 minutes, raise the temperature of the oil bath to 155ºC, and maintain this temperature until 50 mL of the distillate is collected, remove the condenser tube from the fractionation column, rinse with water, wash and merge into the collected liquid, add 3 drops of phenolphthalein indicator solution, and use Titrate until the pH value is 6.9-7.1 (measured with an acidity meter), record the consumed volume V1 (mL), then add 0.5g of sodium bicarbonate and 10mL of dilute sulfuric acid, let it stand until no more carbon dioxide is produced, add 1.0g of potassium iodide, Seal it tightly, shake it well, put it in a dark place for 5 minutes, add 1mL of starch indicator solution, titrate to the end point with sodium thiosulfate titration solution (0.02mol/L), and record the consumed volume V2 (mL). In another blank test, record the volumes Va and Vb (mL) of the consumed sodium hydroxide titration solution (0.02mol/L) and sodium thiosulfate titration solution (0.02mol/L) respectively. Calculate the hydroxypropoxyl content.
Post time: Apr-14-2023