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4.
The mass fraction w 2 of formic acid , the value is expressed in %, calculated according to formula (2):
Where:
V 0 —The value of the volume of sodium thiosulfate standard titration solution (4.
V 1 —The value of the volume of the sodium thiosulfate standard titration solution consumed by the sample in 4.
V 2 —The value of the volume of sodium thiosulfonium standard titration solution consumed in the blank test in 4.
V 3 —The value of the volume of the sodium thiosulfate standard titration solution consumed by the sample in 4.
c—The exact value of the concentration of sodium thiosulfate standard titration solution, the unit is moles per liter (mol/L);
V 4 —The value of the volume of the sample taken for the determination of the total reduction, the unit is milliliters (mL);
V 5 —Measure the value of the volume of the sample taken from other reducing substances except formic acid , the unit is milliliter (mL);
p—The value of the density of the sample at 20°C, in grams per cubic centimeter (g/cm);
M— The value of the molar mass of formic acid (1/2CH 2 O 2 ): the unit is grams per mole (g/mol[M(/2CH 2 O 2 )=23.
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.
Using gas chromatography, under selected working conditions, the sample is vaporized and passed through the chromatographic column to separate the rectifications.
4.
4.
4.
4.
4.
4.
6.
2.
2.
5 Carrier: GDX-103.
(0.
18~0.
25)mm
.
4.
6.
2.
3 Instruments
4.
6.
2.
3.
1 Gas chromatograph: equipped with a thermal conductivity detector, the sensitivity and stability of the whole machine comply with the relevant regulations in GB/T9722-2006;
4.
6.
2.
3.
2 Recorder: chromatographic data processor or chromatographic workstation;
4.
6.
2.
3.
3 Micro glass syringe, 10uL
.
4.
6.
2.
4 Chromatographic column and typical chromatographic operating conditions
The recommended chromatographic column and typical operating conditions are shown in Table 2.
The relative mass correction factor determination is shown in Appendix C.
The relative retention value of each component on the chromatographic column (sebacic acid/GDX103) is shown in Table 3, and the typical chromatogram is shown in Figure 2
.
Other chromatographic columns and operating conditions that can achieve the same degree of separation can also be used
.
Table 2 Chromatographic column and typical operating conditions
Figure 2 Typical chromatogram of formic acid in industrial glacial acetic acid
Table 3 Relative retention time
4.
6.
2.
5 Analysis steps
4.
6.
2.
5.
1 Preparation of test samples
Draw 10mL sample into a small Erlenmeyer flask with stopper and weigh it to the nearest 0.
0002g.
Add 10uL internal standard ethyl acetate (or an amount equivalent to the peak area of formic acid) and weigh it to the nearest 0.
0002g.
Mix the sample
.
4.
6.
2.
5.
2 Determination
According to the instrument manual, adjust the instrument according to the conditions in Table 2, and start sample injection analysis after the instrument is stable
.
The injection volume is 5uL (or determined according to the content of formic acid in the sample), and the calculation result is processed by a chromatographic data processor or an integrator
.