Glycolic acid test method is as below.
1. Method summary
The sample Glycolic acid is titrated with phenolphthalein as indicator.
2. Reagent
Sulfuric acid standard titration solution: C (1 / 2h2so4) about 0.5mol/l Sodium hydroxide standard titration solution: C (NaOH) about 0.5mol/l Phenolphthalein indicator solution: 10g / L
3. Analysis steps
Weigh about 1.0 g (accurate to 0.0001 g) of the sample into a 250ml conical flask, wash the inner wall with a small amount of water and dissolve it. Add 40ml sodium hydroxide standard solution, add 2 drops of phenolphthalein indicator, and titrate with 0.5mol/l sulfuric acid standard titration solution until the red color just disappears.
At the same time of determination, carry out blank test with the same amount of reagent solution without sample according to the same steps as the test sample.
4. Calculation of results
The mass fraction W1 of the content of glycolic acid, expressed in%, is calculated according to below formula :
W1=C×(V0-V)×76.05/ (m*1000)*100%
C — accurate value of concentration of sulfuric acid (1 / 2h2so4) standard titration solution, unit: mol / L
V0 — volume value of sulfuric acid standard titration solution consumed in blank test, unit: ML V — volume of sulfuric acid standard titration solution consumed by sample, unit: ML
m — value of sample mass, unit: G
76.05 — value of molar mass of glycolic acid, unit: g / mol
Take the arithmetic mean of the two parallel determination results as the determination results, and the absolute difference between the two parallel determination results shall not be greater than 0.2%.
