Determination of lactic acid - neutralization titration method

Principle of the method: the test sample dissolved in water, and then precision by adding sodium Ethyl lactate solution (1mol / L) 25mL, boil for 5 minutes, add 2 drops of phenolphthalein indicator solution, hot sulfuric acid titration solution (0.5mol / L) titration, and titration of the blank test correction, phenolphthalein indicator solution turns red stop titration, read sulfuric acid titrant, calculate the lactic acid content.
Reagents: (1) water (boiling placed to room temperature)
(2) sodium hydroxide solution (1mol / L)
3 sulfuric acid titration solution (0.5mol / L)
4 phenolphthalein indicator solution
5 methyl red - bromocresol green mixed indicator solution
6 Ethanol
7 benchmark potassium hydrogen phthalate
8 benchmark anhydrous sodium carbonate
Equipment:
Sample Preparation: 1. Sodium hydroxide solution (1mol / L)
Preparation: Take clarified saturated solution of sodium hydroxide 56mL, add boiling over cold water to make into 1000mL.
Calibration: in 105 ℃ drying to constant weight basis of potassium hydrogen phthalate about 6g, accurately weighed, add boiling over cold water 50mL, shake, to try to dissolve; add 2 drops of phenolphthalein indicator solution, with the droplets, close to the end, should make potassium hydrogen phthalate is completely dissolved, the solution was titrated to pink. Each 1mL of sodium hydroxide (1mol / L) is equivalent to 204.2mg of potassium hydrogen phthalate. According to the liquid magnessium lactate potassium hydrogen phthalate and dosage, calculate the concentration of the solution.
Storage: polyethylene plastic bottle, sealed and stored; plug two holes, each hole insert the glass one, one with soda lime tube connected to a suction of the fluid for use.
2 acid titration solution (0.5mol / L)
Preparation: Sulfate 30mL, slowly inject the right amount of water, cooled to room temperature, diluted with water to 1000mL, shake.
Calibration: at 270-300 ℃ drying to constant weight basis anhydrous sodium carbonate is about 1.5g, accurately weighed, add water to dissolve 50mL, add methyl red - bromocresol green mixed indicator solution 10 drops of the droplet to solution from green to purple, boil for 2 minutes, cooled to room temperature and continue the titration until the solution color green to dark purple. Each 1mL of sulfuric acid titration solution (0.5mol / L) is equivalent to 53.00mg of anhydrous sodium carbonate. According to the liquid consumption of anhydrous sodium carbonate dosage, zinc lactate the concentration of the solution, that is, too.
3 phenolphthalein indicator solution
Take phenolphthalein 1g, plus ethanol 100mL dissolve.
4 bromocresol green mixed indicator solution
0.1% methyl red ethanol solution of 20mL, plus 0.2% bromocresol green in ethanol 30mL, shake, that, too.
Procedure: Weigh the test sample 1g, accurately add water 50mL, precision by adding sodium hydroxide solution (1mol / L) 25mL, boiled for 5 minutes, add 2 drops of phenolphthalein indicator solution, hot sulfuric acid titration solution (0.5mol / L) titration, to the solution was pink, and titration of the blank test correction, record consumption of sulfuric acid titrant volume number (mL), each 1mL of sodium hydroxide (0.1mol / L) is equivalent to 90.08mg lactic acid (C3H6O3).
Note 1: "Precision Weigh" means to check the weight should be accurately referred to take the weight of one-thousandth, "precise amount" means the amount of volume accuracy should be in line with national standards for the volume pipettes accuracy requirements.