GB 31604.22-2016Method for analysis of hygienic standard of products of foamed polystyrene for food packaging (English PDF)

3.1 Reagents

3.1.1 N, N-dimethylacetamide (C4H9NO). chromatographically pure.

3.2 Standard

Dichlorodifluoromethane (CCl2F2) (CAS Number. 75-71-8). The purity >99%.

3.3 Preparation of standard solutions

3.3.1 Standard stock solution of dichlorodifluoromethane (100 µg/mL).

Accurately WEIGH 1 mg (accurate to 0.01 mg) of dimethylacetamide standard in a 10 mL brown volumetric flask; USE N, N-dimethylacetamide to dissolve and dilute to volume; and MIX well. At 4 °C, STORE it for 1 year.

c) Inlet temperature. 250 °C;

d) Detector temperature. 300 °C;

e) Carrier gas. nitrogen; the purity is greater than or equal to 99.999%.

Constant current mode; flow rate. 1.0 mL/min;

f) Injection volume. 1.0 mL, split injection; the split ratio is 20.1;

g) Make-up gas. nitrogen, 60 mL/min.

5.3 Making of standard curve

ADD 3 mL of N, N-dimethylacetamide in each of 5 equilibration flasks; CAP the plugs; USE a microsyringe to take 0 µL, 3 µL, 15 µL, 30 µL, 150 µL, 300 µL of standard working solution of dichlorodifluoromethane (1 µg/mL) and INJECT into the flasks through rubber plug; gently SHAKE well and PUT in a constant temperature water bath at 65 °C to equilibrate for 15 min. The standard curve concentrations are 0 ng/mL, 1 ng/mL, 5 ng/mL, 10 ng/mL, 50 ng/mL,100 ng/mL.

Respectively TAKE 1 mL of the head space gas and INJECT into gas chromatograph; TAKE the dichlorodifluoromethane content as the abscissa;

TAKE the peak area as the ordinate and DRAW standard curve. The gas chromatogram of dichlorodifluoromethane standard solution is as shown in

Figure A.1.

5.4 Determination of sample solution

Manually or automatically INJECT the head space gas, which contains 1 mL of the sample, into gas chromatograph to determine; and OBTAIN the peak area.

According to the standard curve, OBTAIN the content of dichlorodifluoromethane in the sample solution. At the same time, CARRY out blank test.