1 subject content and scope of application
The standard specifies the method for determining the glycerol content in sweet water.
This standard applies to the determination of glycerin content in sweet water and distilled glycerin.
2 principle
The hydroxy group causes oxidation of glycerol to formaldehyde and formic acid according to potassium periodate, and potassium periodate is reduced to potassium iodate in this case.
The remaining potassium periodate and potassium iodate were freed from iodine by adding potassium iodide under strong acidic conditions, and then titrated with a standard Na2S203 solution, using starch as an indicator.
It can be seen from the reaction that 1 mol of KI04 can release 4 mol of I2 and 1 mol of KIO3 releases 3 mol of I2: glycerol reacts only 1/4 of the free iodine, so when titrating the sample, the volume of the standard solution is consumed. Should not exceed 3/4 of the blank, more than 3/4 result is low.
3 instruments
1 Volumetric flask 500ml 2 Iodine volumetric flask 500 ml 3 Transfer night tube 25ml 4 Burette 50ml 5 Measuring cylinder 20 ml
4 reagents
1 potassium iodide: 10% aqueous solution;
2 starch indicator
3 sodium thiosulfate: 0.1N standard solution;
4 20% hydrochloric acid solution:
5 0.1N potassium periodate solution
5 test procedures
Accurately weigh 4g of sample on the analytical balance and put it in a 500 ml volumetric flask, dilute to the mark and shake it, then take 25ml into the iodine volumetric flask; add 25N of 0.1N KIO4 solution, leave it for 15 minutes, add 20% hydrochloric acid. 20 ml of solution, 20 ml of 10% potassium iodide solution, allowed to stand for 15 minutes, then titrated with 0.1 mol of L Na2S2O3, standard solution to pale yellow, 1 ml of starch indicator was added, and the titration was continued until the blue color disappeared. At the same time, a blank test was performed under the same conditions.
6 calculation method
Where: B: volume of sodium thiosulfate standard solution used in the blank test
C: concentration of sodium thiosulfate standard solution mol/L M: sample mass, g 0.023024 – milligram equivalent of glycerol Parallel test tolerance 0.5. 12.6 Analysis method of crude glycerin The method is the same as above, except that the sample is weighed (0.2 to 0.4) g.
