HJ 697-2014Water quality. Determination of acrylamide. Gas chromatography method (English PDF)

5.5 Potassium Bromide (KBr)

5.6 Potassium bromate solution. c (KBrO3) = 0.1 mol/L.

Weigh 1.67 g of potassium bromate dissolved in a small amount of water and dilute to 100 ml.

5.7 Sodium thiosulfate solution. c (Na2S2O3) = 1.0 mol/L.

Weigh 15.8 g of sodium thiosulfate in a small amount of water and dilute to 100 ml.

5.8 Anhydrous sodium sulfate (Na2SO4)

After burning at 400 ° C for 4 h, it was cooled and placed in a ground glass bottle and stored in a desiccator.

5.9 Silicon Magnesium Adsorbent

60-100 mesh, fired at 300 ° C for 2 h, naturally cooled, placed in a ground glass bottle, and stored in a desiccator.

5.10 Nitrogen. purity >= 99.999%.

7.1 Sample collection and preservation

Samples were taken with reference to the relevant regulations of HJ/T 91 and HJ/T 164.

Collect 250ml samples in clean ground glass bottles or brown threaded glass bottles with Teflon septa at 2°C Store at ~5 °C, extract within 7 days, and extract for 30 days.

7.2 Preparation of samples

7.2.1 Measure 100.0ml sample into a 250ml iodine measuring flask, add 6.0ml sulfuric acid solution (5.4), mix, 2 ° C ~ 5 ° C Place for 30 min.

7.2.2 Take out the iodometric flask, add 15.0g potassium bromide (5.5), dissolve and add 10ml potassium bromate solution (5.6) to mix, 2 ° C Leave at ~5 °C for 2 h.

7.2.3 Take out the iodometric flask and add sodium thiosulfate solution (5.7) dropwise while shaking until the solution becomes colorless.

7.2.4 Add a magnetic stirrer to the iodine flask and slowly add 30g of anhydrous sodium sulfate (5.8) with vigorous stirring of the magnetic stirrer.

After completely dissolved, the stopper was allowed to stand for 10 min.

Note 1. Anhydrous sodium sulfate cannot be agglomerated during the addition of anhydrous sodium sulfate.

7.2.5 Transfer the above test solution to a 250ml separatory funnel, rinse the iodometric flask with about 2ml of water, and transfer the eluent to the liquid separation.

In the funnel, rinse twice.

7.2.6 Add 25 ml of ethyl acetate (5.1) to the separatory funnel, shake it and place it on a shaker for 5 min.

The layers were separated for 10 min and the organic phase was transferred to a 100 ml beaker. Repeat the extraction twice more.

7.2.7 Purification and drying. 10 g of silica-magnesium adsorbent (5.9) and 4 g of anhydrous sodium sulfate (5.8) were added successively to the drying column (6.7).

The dry column was immersed in a small amount of ethyl acetate, and the bubbles were discharged by pressure or vibration. When the ethyl acetate level is close to the dry column packing at the time, the organic phase (7.2.6) was added and the organic phase was collected in a 150 ml concentrate bottle and washed with a small amount of ethyl acetate (5.1).

Cup, over dry column, repeat 1~2 times, then wash the dry column with 2 times of ethyl acetate for 2~3 times, collect all organic phase to thick Shrink the bottle.

7.2.8 Using the rotary evaporator (reference conditions. water bath temperature 50 ° C, vacuum 270 mbar) the above organic phase (7.2.7) the extract is concentrated to about 5 ml, the concentrate is transferred to a 10 ml volumetric flask, and the concentrate bottle is washed with a small amount of ethyl acetate (5.1).

2~3 times, transfer to the volumetric flask, and then make up to 10.0ml with ethyl acetate, to be tested.

7.2.9 Another 100.0ml of the same sample was placed in a 250ml separatory funnel and directly extracted according to the steps 7.2.6 to 7.2.8.

Take, concentrate and make up.

Note 2. This step is used to determine the content of alpha,beta-dibromopropionamide which may be contained in the sample equivalent to acrylamide.

7.3 Preparation of blank samples

A sample of 100.0 ml of distilled water was used instead of the sample, and a blank sample was prepared in accordance with the same procedure as in the preparation of the sample (7.2).

8.1 Recommended chromatographic conditions

Inlet temperature. 225 ° C; split injection, split ratio 10.1; column flow rate. 1.5 ml/min; oven temperature.

30/min 20/min100 min min 240 min----> ---->°C °C(4) 220°C(5) °C(5); detector temperature. 280°C;

Injection volume. 1.0 µl.

8.2 Drawing the working curve

The working curve should be drawn using acrylamide standard solution (5.2) each time the sample is analyzed. Take 6 250ml iodine Bottles, add 100ml of pure water, add 0.00µl, 5.00µl, 10.0µl, 25.0µl, 50.0µl, 125.0µl acryloyl the standard solution of the amine is used (4.12), and the mass concentration of acrylamide is 0.00µg/L, 0.50µg/L, 1.00µg/L, respectively.

2.50 µg/L, 5.00 µg/L, 12.5 µg/L standard series. According to the preparation step (7.2) of the sample, according to the recommendation the chromatographic conditions (8.1) were determined by using the concentration of the standard solution series (µg/L) as the abscissa and the corresponding chromatographic peak the working curve is drawn by the value (peak area/peak height) as the ordinate.

8.3 Determination of samples

Take 1.0 µl of the sample to be tested (7.2) into the gas chromatograph, measure according to the recommended chromatographic conditions, and record the chromatographic peak.

Retention time and peak area (or peak height).

8.4 Blank test

While the sample is being analyzed, a blank test should be performed. Take 1.0µl blank sample (7.3) into the gas chromatograph, push the recommended chromatographic conditions were determined and the retention time and peak area (or peak height) of the chromatographic peaks were recorded.

9.1 Qualitative analysis

During the addition reaction of acrylamide with bromine to form alpha,beta-dibromopropionamide, other brominated products are produced and used.

The sub-capture detector detects impurity peak interference when it is detected, which is inconvenient for the quasi-determinism of acrylamide. Take an appropriate amount of alpha,beta-dibromopropionamide Standard solution (5.3), diluted to 20 µg/L with ethyl acetate, according to the recommended chromatographic conditions (8.1), according to the Leave time to characterize, see Figure 1.

Figure 1 Standard chromatogram of alpha,beta-dibromopropionamide (column 1)

Figure 2 Sample Derived Chromatogram (Column 1)

When acrylamide is detected in the sample, it can be confirmed with column 2.

Figure 3 Sample Derived Chromatogram (Column 2)

9.2 Calculation of results

The mass concentration (µg/L) of acrylamide in the sample was calculated according to the formula (1).

rho rhorho -= × (1)

In the formula.

rho--the mass concentration of acrylamide in the sample, µg/L;

rho1-- From the sample (7.2.8) found on the working curve, alpha,beta-dibromopropionamide corresponds to the mass concentration of acrylamide.

Gg/L;

rho2--alpha,beta-dibromopropionamide corresponding to the mass concentration of acrylamide in the sample (7.2.9) found on the working curve, Gg/L;

V1--water sample volume, ml;

V2--sample volume, ml.

9.3 Result representation

When the measurement result is >=1.00µg/L, three significant figures should be retained; when the measurement result is