Glacial acetic acid for industrial use (5)

4.

Internal standard method

4.

The mass fraction of formic acid w ₃ , the value is expressed in %, calculated according to formula (3):

Where

m _s —The mass of internal standard ethyl acetate , in grams (g);

A _i —formic acid peak area;

f _i — relative mass correction factor of formic acid and internal standard ethyl acetate;

A _s —the peak area of ​​the internal standard ethyl acetate ;

m—The quality of the sample

Take the arithmetic mean of the two parallel determination results as the determination result, and the difference between the two parallel determination results shall not exceed 0.

4.

4.

The acetaldehyde in the sample reacts with excess sodium bisulfite solution, and the remaining sodium sulfite is determined by iodometric method.

4.

4.

Weigh 1.

4.

4.

4.

4.

4.
7.
3.
1 Pipette 10mL sample, place it in a 50mL volumetric flask already filled with 10mL water, add 5mL sodium bisulfite solution, dilute to the mark with water, mix well and let stand for 30min
.
It is the test solution
.

4.
7.
3.
2 Pipette 50 mL of iodine standard solution into an iodine measuring flask, and place it in an ice water bath to stand still
.
Take 20 mL of the test solution in an iodine flask, titrate with sodium thiosulfate standard titration solution until the solution is light yellow, add 0.
5 mL starch indicator solution, and continue titration until the blue color just disappears as the end point
.

4.
7.
3.
3 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 steps as the measurement
.

4.
7.
4 Result calculation

The mass fraction of acetaldehyde w ₄ , the value is expressed in %, calculated according to formula (4):

Where:

V ₀ —The value of the volume of the sodium thiosulfate standard titration solution (4.
7.
2.
3) consumed in the blank test, in milliliter (mL);

V ₁ —The value of the volume of the standard titration solution of sodium thiosulfate consumed by the sample, in milliliters (mL);

c—The exact value of sodium thiosulfate standard titration solution, the unit is mole per liter (mol/L);

M— The value of the molar mass of acetaldehyde (1/2C ₂ H ₄ O), in grams per mole (g/mol) [M(1/2C ₂ H ₄ O)=22.
03];

V—the value of the volume of the sample, the unit is milliliters (mL);

p—The value of the density of the sample at 20°C, in grams per cubic centimeter (g/cm)
.

Take the arithmetic average of the two parallel determination results as the determination result, and the difference between the two parallel determination results shall not exceed 0.
002%
.

Related links: Glacial acetic acid for industrial use (4)