Ashing method for measuring sodium carboxymethyl cellulose

Before using sodium carboxymethyl cellulose, in order to ensure the performance of the product, it is necessary to measure it in advance. There are many methods for measuring CMC-Na, and the ashing method is a frequently used method. However, to ensure the accuracy of measurement, specific knowledge can be learned from the following.
1. Principle: The purified sodium carboxymethyl cellulose is calcined at (700 soil 25) ℃ to obtain residual sodium oxide, and then the sodium oxide content is titrated with acid and alkali, and the degree of substitution is calculated based on the sodium oxide content.
2. Instruments and reagents: high-temperature furnace (0-1000 ℃), burette (50ml), beaker (300ml), 3 # glass sand core crucible (30ml), suction filtration bottle (1000ml), air extraction pump, 0. lmol/L NaOH standard solution, 0. lmol/L HCl standard solution, 0. l% methyl red.
3. Operating Steps: Weigh about 1.2 g of sodium carboxymethyl cellulose into a 300 ml beaker, add 20 ml of 0.5 mol/L HCl solution for acidification, fully stir for 15 minutes until there are no particles, add a few drops of phenolphthalein indicator, neutralize with 0.5 mol/L NaOH solution until red, continue stirring until the sample is dissolved, and then drop three drops of 0.5 mol/L NaOH solution. Add 95% ethanol solution while stirring. When white precipitates appear in the test solution, quickly add about 200 ml of 95% ethanol solution to precipitate. Stop stirring and heat on a water bath to make the sediment clear and coarse.
Transfer the precipitate into a 3 # glass sand core crucible, filter it, wash it with 80% ethanol several times (about 100ml), then wash it with 95% ethanol three times (about 60ml), absorb it, transfer it into an oven, bake it at 105 ℃ until the mass is constant (about 3h), cool and weigh it.
Pour the weighed dry pure sodium carboxymethyl cellulose into a dry 30ml porcelain crucible, place it in a high-temperature furnace, slowly raise the temperature to 700 ℃, hold for 30min, and take it out to cool to room temperature.
Wet the burned substance with a small amount of distilled water, wash it several times with 100ml of distilled water, and transfer it to a 250ml beaker. Heat it slowly on an electric stove until it boils, and keep it for 5min. Add 2-3 drops of methyl red indicator and titrate with 0. lmol/L HCl standard solution to the end point.
Therefore, the operating principle and method of the sodium carboxymethyl cellulose ashing method are strictly followed, which can ensure the accuracy of the product measurement and provide convenience for subsequent work.