4.
6.
2.
6 Quantitative method
Internal standard method
.
4.
6.
2.
7 Result calculation
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.
005%
.
4.
7 Determination of acetaldehyde content by titration
4.
7.
1 Method summary
The acetaldehyde in the sample reacts with excess sodium bisulfite solution, and the remaining sodium sulfite is determined by iodometric method.
Reaction formula:
4.
7.
2 Reagents
4.
7.
2.
1 Sodium bisulfite solution: 18.
2g/L
.
Weigh 1.
66 g of sodium metabisulfite and dissolve it in a 100 mL volumetric flask containing 50 mL of water.
After dissolution, dilute to the mark with water and mix
.
4.
7.
2.
2 Iodine standard solution: c(1/2I 2 )=0.
02mol/L
.
4.
7.
2.
3 Sodium thiosulfate standard titration solution: c(Na 2 S 2 O 3 )=0.
02mol/L
.
4.
7.
2.
4 Starch indicator solution: 10g/L
.
4.
7.
3 Analysis steps
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)
