1 Scope
This standard specifies the gas chromatography method for the determination of formic acid in industrial glacial acetic acid.
This standard applies to the determination of formic acid content in industrial glacial acetic acid products.
2. Method summary
The components in industrial glacial acetic acid are separated on sebacic acid / GDX103 column and detected by thermal conductivity detector. Ethyl acetate is the internal standard substance and quantified by internal standard method.
3. Reagents and materials for determination of formic acid content in industrial glacial acetic acid by gas chromatography
3.1 Hydrogen: purity 99.9% (V / V).
3.2 Reagent
3.2.1 Formic acid: chromatographically pure.
3.2.2 Ethyl acetate: chromatographically pure.
3.2.3 Glacial acetic acid: pure grade.
3.2.4 Potassium permanganate: analytically pure.
3.2.5 Absolute ethanol: analytically pure.
3.2.6 Fixative: Sebacic acid.
3.2.7 Carrier: GDX103, aperture 0.18 ～ 0.25mm.
4. Instrument for determination of formic acid content in industrial glacial acetic acid
4.1 Gas chromatograph (Hunan Chuangte).
4.2 Detector: Thermal conductivity detector.
4.3 Recorder: 1mV full scale, or chromatographic data processor.
4.4 Column
4.4.1 Column tube: 1.5 ～ 2.0m, stainless steel tube or borosilicate glass tube with inner diameter of 2 ～ 3mm.
4.4.2 filler
Fixative: carrier = 7: 100.
Method of applying fixative solution: Weigh 0.28g sebacic acid, place it in a 200mL beaker, add about 23mL of absolute ethanol to dissolve, then add 4.0g carrier to completely immerse the carrier, stir a little, and slowly evaporate the solution on the water bath To dry, and then moved to 100 ℃ electric thermostat drying oven for 2h.
4.4.3 Filling method
Put the glass wool on the outlet end (connected to the detector end) of the chromatographic column, connect the vacuum pump, connect the funnel to the other end, turn on the vacuum pump, and put it into the stationary phase under gentle vibration, filling evenly and tightly. The filling amount is about 2g. Then plug it with glass wool.
4.4.4 Chromatographic column aging
Install the packed chromatographic column in the chromatograph oven, the outlet is disconnected from the detector, and aging at 120 ℃ for more than 8h until the baseline is stable.
4.5 Sampler
Micro glass syringe: volume 10μL, minimum division 0.2μL.
5. Analysis steps for determination of formic acid in industrial glacial acetic acid by gas chromatography
5.1 Operating conditions of chromatograph
Adjust the instrument according to the following conditions, allow appropriate changes according to different instruments, and obtain appropriate resolution.
5.1.1 Temperature of vaporization chamber: 150 ℃.
5.1.2 Temperature of testing room: 150 ℃.
5.1.3 Oven temperature: 110 ℃.
5.1.4 Bridge current: 135mA.
5.1.5 Carrier gas flow rate: 50mL / min.
5.2 Quantitative method: internal standard method.
5.2.1 Preparation of standard samples
5.2.1.1 Glacial acetic acid without formic acid: Add 1g of potassium permanganate to 1000mL of glacial acetic acid reagent to decompose formic acid, then distill to remove formic acid.
5.2.1.2 Preparation of standard samples: Pipette 20mL of glacial acetic acid without formic acid into clean and dry 4 to 5 milled glass bottles, add formic acid standard sample and ethyl acetate standard sample with a micro syringe , So that the peak areas of the two components are close to each other). Weigh them in increments, accurate to 0.0002g, and mix. Prepared during measurement.
5.2.2 Determination of correction factor
After the operating conditions of the instrument are stable, draw 5μ respectively, each standard sample is injected, and the first needle saturates the column. After the peak is completed, the correction factor is calculated. The measurement result is based on the 95% confidence level, and the average value is calculated. The correction factor should be calibrated regularly.
5.2.3 Calculation of correction factor
The relative correction factor fi of formic acid is calculated according to formula (1):
As? Mi
fi = -----
Ai? Mi
In the formula: fi--the relative correction factor of the quality of formic acid and the internal standard ethyl acetate;
As--peak area of ​​ethyl formate, cm2;
mi--the quality of formic acid standard sample, g;
Ai--peak area of ​​formic acid, cm2.
5.3 Test
5.3.1 Preparation of samples
Draw 10mL of the sample into a small triangular flask with a stopper and weigh it to the nearest 0.0002g. Add 10μL of internal standard ethyl acetate (or equivalent to the formic acid peak area) to weigh it to the nearest 0.0002g.
5.3.2 Injection
Perform analysis after the instrument operating conditions are stable. Advance one needle sample to saturate the column, and then enter two needle samples for analysis. The injection volume is 5 μL (or according to the amount of formic acid in the sample).
6. Chromatogram and relative retention time
6.1 Chromatogram (omitted)
Air; 2-hydroaldehyde; 3-carboxylic acid; 4-ethyl acetate; 5-acetic acid
6.2 Relative retention time
The relative retention time of each component on the chromatography column (Sebacic acid / GDX-103) is shown in Table 1.
Table 1 Relative retention time
Peak order component name relative retention time
1 Air 0
2 aldehyde 0.07
3 formic acid 0.70
4 ethyl acetate 1.00
5 acetic acid 1.30
7. Expression of analysis results of formic acid content in industrial glacial acetic acid by gas chromatograph
The formic acid content X1 expressed in mass percentage is calculated according to formula (2), or the effect is calculated with a data processor:
Ai? Fi? Ms
X1 = ------ × 100 ……………………………… (2)
An? M
In the formula: X1-percentage of formic acid in the sample,%;
ms--the mass of ethyl acetate added to the internal standard, g;
Ai--Formic acid peak area, cm2;
fi--the quality correction factor of formic acid and internal standard ethyl acetate;
An--Peak area of ​​the internal standard ethyl acetate, cm2
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