Industrial L-cystine (2)

4 Test method

The reagents and water used in this standard, unless other requirements are specified, use analytical reagents and distilled water or water of equivalent purity

The standard solutions, preparations and products used in this standard shall be prepared according to the methods specified in GB601, GB602, and GB603 unless other requirements are indicated

4.

4.

4.

4.

Weigh 1.

Temperature correction factor: +1.

4.

4.

4.

4.

4.

Weigh 0.

4.

4.

Bromine can oxidize cystine to a-amino-β sulfo-propionic acid.
Excess bromine oxidizes the iodide ion of potassium iodide to free iodine.
The amount of iodine can be determined by iodometry, so that the indirect of cystine can be carried out .
Determination
.

The response is as follows:

4.
3.
2 Reagents and solutions

4.
3.
2.
1 Sodium hydroxide solution: 10g/L;

4.
3.
2.
2 Hydrochloric acid ;

4.
3.
2.
3 Potassium iodide solution: 450g/L, prepared when used;

4.
3.
2.
4 Bromine solution: c(Br ₂ )=0.
1mol/L, weigh 3g potassium bromate and 15g potassium bromide, add water to dissolve it into 1000mL, and store it in a brown bottle;

4.
3.
2.
5 Starch solution: 5g/L, freshly prepared;

4.
3.
2.
6 Standard titration solution of sodium thiosulfate : c(Na ₂ S ₂ O ₃ )=0.
1mol/L
.

4.
3.
3 Analysis steps

Weigh 0.
3 g (accurate to 0.
0002 g) of the sample dried according to Article 4.
1.
2, add 10 mL of sodium hydroxide solution to dissolve, transfer it into a 100 mL volumetric flask, add water to dilute to the mark, and shake well
.
Pipette 25.
0mL of this solution into an iodine flask, add 50.
00mL bromine solution, add 10mL hydrochloric acid, cap immediately, shake well, place in a dark place for 10 minutes, then cool in an ice bath for more than 3 minutes, add 5mL potassium iodide, and use immediately The standard titration solution of sodium thiosulfate is titrated to light yellow, 2 mL of starch solution is added, and the drop is continued until the blue color disappears as the end point
.
At the same time, make a blank test
.

4.
3.
4 Calculation of analysis results

The content (X) of L-cystine (C ₆ H ₁₂ O ₄ N ₂ S ₂ ) expressed in mass percentage is calculated as follows:

In the formula: V ₁ -the volume of the sodium thiosulfate standard titration solution consumed in the blank test, mL;

V ₂ ——The volume of sodium thiosulfate standard titration solution consumed by sample titration, mL;

c — Concentration of sodium thiosulfate standard titration solution, mol/L;

m—the mass of the sample, g;

0.
02403 — The mass of L-cystine expressed in grams equivalent to 1.
00mL sodium thiosulfate standard titration solution [c(Na ₂ S ₂ O ₃ )=1.
000mol/L] .

4.
3.
5 Tolerance

The difference between the two parallel determinations is not more than 0.
2%, and the arithmetic mean is the determination result
.

4.
4 Determination of chloride content

4.
4.
1 Principle

Chloride ions and silver ions generate white silver chloride precipitates in acidic solutions , which can be used for visual turbidity limit inspection
.

4.
4.
2 Reagents and solutions

4.
4.
2.
1 Nitric acid solution: 1+9;

4.
4.
2.
2 Silver nitrate solution: 17g/L;

4.
4.
2.
3 Chloride standard solution: 1mL solution contains 0.
1mg Cl
.

4.
4.
3 Analysis steps

Weigh 0.
100g of the sample (accurate to 0.
001g) in a Na's colorimetric tube, add 10mL of nitric acid solution to dissolve, add water to dilute to 25mL
.

The following is determined according to the "Chloride Inspection Method" in the appendix of the Pharmacopoeia of the People's Republic of China
.