Determination of Nb in methanol in industrial glac

Determination of methanol in industrial glacial acetic acid by gas chromatography nbsp

determination of formic acid content in industrial glacial acetic acid gas chromatography

glacial acetic acid for industrial use Determination of formicacid content gaschromatography method

1 Scope

this standard specifies the gas chromatography method for the determination of formic acid content in industrial glacial acetic acid

this standard is applicable to the determination of formic acid content in industrial glacial acetic acid products

2 method summary

each component in industrial glacial acetic acid is separated on sebacic acid/gdx103 column, detected by thermal conductivity detector, ethyl acetate is the internal standard, and quantified by internal standard method

3 reagents and materials

3.1 different results may be obtained under the same experimental conditions hydrogen: purity 99.9% v/v

3.2 reagent

3.2.1 formic acid: chromatographic purity

3.2.2 ethyl acetate: chromatographic pure

3.2.3 glacial acetic acid: superior pure

3.2.4 potassium permanganate: analytically pure

3.2.5 absolute ethanol: analytically pure

3.2.6 stationary solution: sebacic acid

3.2.7 carrier: gdx103, aperture 0.18 ~ 0.25mm

4 instrument

4.1 gas chromatograph

4.2 detector: thermal conductivity detector

4.3 recorder: the full scale is 1mV, or chromatographic data processor

4.4 chromatographic 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

fixed liquid: carrier =7:100

method of coating the fixed solution: weigh 0.2. 8g sebacic acid, which is restricted, is placed in a 200ml beaker, add about 23ml absolute ethanol to dissolve, then add 4.0g carrier to completely immerse the carrier, stir slightly, slowly volatilize the solution on a water bath until it is dry, and then move it to a 100 ℃ electric constant temperature drying oven for 2h

4.4.3 filling method

plug the outlet end of the chromatographic column (connected to the detector end) with glass wool, connect the vacuum pump, and connect the funnel at the other end, turn on the vacuum pump, install the stationary phase under slight vibration, and fill it evenly and tightly. The filling amount is about 2G. Then plug it with glass wool

4.4.4 chromatographic column aging

install the filled chromatographic column in the chromatographic column box, disconnect the outlet from the detector, and aging at 120 ℃ for more than 8h until the baseline is stable

4.5 sampler

micro glass syringe: capacity 10 μ 50. Minimum graduation 0.2 μ L。

5 analysis steps

5.1 operating conditions of the chromatograph

adjust the instrument according to the following conditions, allowing appropriate changes according to different instruments, and the appropriate resolution should be obtained

5.1.1 vaporization chamber temperature: 150 ℃

5.1.2 detection of room temperature and temperature: 150 ℃

5.1.3 column box 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 potassium permanganate to 1000ml glacial acetic acid reagent, decompose formic acid, and then distill to remove formic acid

5.2.1.2 preparation of standard sample: take 20ml of glacial acetic acid without formic acid into 4-5 clean and dry ground glass bottles, add formic acid standard sample and ethyl acetate standard sample with a micro syringe (the amount is more than formic acid, so that the peak areas of the two components are close), weigh with an increase method, accurate to 0.0002g, and mix well. Prepare during determination

5.2.2 determination of correction factor

after the operating conditions of the instrument are stable, absorb 5% respectively μ， For each standard, such as glass, metal and hard plastic packaging, inject samples for analysis, saturate the chromatographic column with the first needle, and calculate the correction factor after the peak is finished. The determination results are chosen according to the confidence of 95%, and the average value is obtained. 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

where: fi - the relative correction factor of the mass of formic acid and the internal standard ethyl acetate

as -- peak area of ethyl formate, cm2

mi -- mass of formic acid standard sample, G

ai -- peak area of formic acid, cm2

5.3 test

5.3.1 preparation of sample

suck 10ml of sample and weigh it in a small triangular flask with a stopper, accurate to 0.0002g, add 10 μ L internal standard ethyl acetate (or the amount equivalent to the peak area of formic acid) is weighed, accurate to 0.0002g, and the sample is mixed

5.3.2 sample injection

analyze after the operating conditions of the instrument are stable. First, one sample is injected to saturate the chromatographic column, and then two samples are injected for analysis. The injection volume is 5 μ L (or determined according to the content of formic acid in the sample)

6 chromatogram and relative retention time

6.1 chromatogram (see Figure 1)

1- air; 2-water + aldehyde; 3-formic acid; 4-ethyl acetate; 5-acetic acid

Figure 1 gas chromatography of formic acid in industrial glacial acetic acid

6.2 relative retention time

each component is on the chromatographic column, The relative retention time on sebacic acid/gdx-103 is shown in Table 1

Table 1 relative retention time

peak sequence component name relative retention time

1 air 0

2 water + aldehyde 0.07

3 formic acid 0.70

4 ethyl acetate 1.00

5 acetic acid 1.30

7 expression of analysis results

formic acid content X1 expressed as mass percentage, calculated according to formula (2), Or use the data processor to calculate the effect:

ai fi ms

x1=—————— × 100.................................. (2)

an m

where: X1 -- percentage content of formic acid in the sample,%

ms -- mass of ethyl acetate added as internal standard, G

ai -- peak area of formic acid, cm2

fi -- quality correction factor of formic acid and internal standard ethyl acetate

an -- peak area of internal standard ethyl acetate, cm2