Dimethyl sulfate for industrial use (2)

5 Test method

5.

Dimethyl sulfate is a highly toxic substance

Some test procedures specified in the test method may lead to dangerous situations, and the operator should take appropriate safety and protective measures

5.

Unless otherwise specified, only reagents confirmed to be analytically pure and grade 3 water specified in GB/T6682-1992 are used in the analysis

The standard titration solutions, preparations and products used in the analysis are prepared in accordance with the provisions of GB/T601-2002 and GB/T603-2002 when other requirements are not specified

5.

5.

A quantitative potassium hydroxide -ethanol standard solution is added to the sample.

Reaction equation: (CH ₃ ) ₂ SO ₄ +KOH→CH ₃ KSO ₄ +CH ₃ OH

2KOH+H ₂ SO ₄ →K ₂ SO ₄ +H ₂ O

5.

5.

5.

5.

5.

Constant temperature water bath: controllable temperature (40±2)℃

5.

Weigh about 0.
6g laboratory sample, accurate to 0.
1mg, and place it in a 100mL iodine measuring flask containing (10±0.
02)mL potassium hydroxide-ethanol standard titration solution, and close the stopper tightly, (40±2)℃ Place it in a constant temperature water bath for 1 hour, add 3 drops of phenolphthalein indicator solution, and titrate with a sulfuric acid standard titration solution.
The red color of the solution just disappears as the end point
.

At the same time of measurement, perform a blank test with the same amount of reagent solution without adding the sample according to the same procedure as the measurement
.

5.
3.
5 Result calculation

The mass fraction w _{1 of} dimethyl sulfate , the value is expressed in %, calculated according to formula (1):

Where:

V ₀ —The value of the volume of the standard titration solution (5.
3.
2.
2) of sulfuric acid consumed in the blank test, in milliliter (mL);

V ₁ —The value of the volume of the sample consumed by the sulfuric acid standard titration solution (5.
3.
2.
2), in milliliter (mL);

c—The exact value of the concentration of the sulfuric acid standard titration solution, the unit is moles per liter (mol/L);

m—The value of the mass of the sample, in grams (g);

M—The value of the molar mass of dimethyl sulfate, in grams per mole (g/mol) (M=126.
13);

u—The acidity value expressed in mass fraction measured according to 5.
4, expressed in (%);

2.
57 —The conversion factor for converting sulfuric acid into dimethyl sulfate
.

Take the arithmetic mean of the two parallel determination results as the determination result
.
The absolute difference between the two parallel determination results is not more than 0.
3%
.

5.
4 Determination of acidity

5.
4.
1 Method summary

Titrate free sulfuric acid in dimethyl sulfate with potassium hydroxide -ethanol standard titration solution
.
According to the volume value of the potassium hydroxide-ethanol standard titration solution, the acidity of the sample is calculated, which is calculated as sulfuric acid (1/2H ₂ SO ₄ )
.

5.
4.
2 Reagents

5.
4.
2.
1 Potassium hydroxide-ethanol standard titration solution: c(KOH)=0.
1mol/L
.

5.
4.
2.
2 Methyl red indicator solution: 1g/L
.

5.
4.
3 Analysis steps

Weigh 3.
0g～4.
0g laboratory sample, accurate to 0.
1mg, place it in a dry 100mL iodine flask, quickly add 3 drops of methyl red indicator solution, and quickly titrate with potassium hydroxide-ethanol standard titration solution to the solution The color changed from red to light yellow
.

5.
4.
4 Result calculation

The acidity is the mass fraction w ₂ in terms of sulfuric acid (1/2H ₂ SO ₄ ) , and the value is expressed in %, calculated according to formula (2):

Where:

V—The value of the volume of the potassium hydroxide-ethanol standard titration solution (5.
4.
2.
1) consumed by the sample, in milliliters (mL);

c— The exact value of the concentration of potassium hydroxide -ethanol standard titration solution, the unit is moles per liter (mol/L);

m—The value of the mass of the sample, in grams (g);

M— The value of the molar mass of sulfuric acid , in grams per mole (g/mol) [M(1/2H ₂ SO ₄ )=49.
04]
.

Take the arithmetic mean of the two parallel determination results as the determination result
.
The absolute difference between the two parallel determination results is not more than 0.
03%
.