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This standard replaces GB/T 5009.100-2003 Method for Analysis of Hygienic Standard of Products of Foamed Polystyrene for Food Packaging.
The following main changes have been made with respect to GB/T 5009.100-2003 (the previous edition):
——This standard is renamed as National Food Safety Standard - Food Contact Materials and Articles - Determination of Dichlorodifluoromethane in Products of Foamed Polystyrene;
——Packing chromatographic column for sample determination is changed into capillary chromatographic column;
——Sensitivity of method is added, and detection limit and quantitation limit are decreased.
National Food Safety Standard
Food Contact Materials and Articles
Determination of Dichlorodifluoromethane in Products of Foamed Polystyrene
1 Scope
This standard specifies the determination method of dichlorodifluoromethane in products of foamed polystyrene.
This standard is applicable to the determination of dichlorodifluoromethane in products of foamed polystyrene.
2 Principle
In accordance with relevant gas laws, put the specimen into a sealed equilibration flask and dissolve with solvent. Under certain temperature, dichlorodifluoromethane diffuses, when it reaches equilibrium, inject gas above solution into gas chromatograph for determination.
3 Reagents and Materials
Unless otherwise specified, analytically-pure reagents and Class-II water (defined in GB/T 6682) are adopted for the purpose of this method.
3.1 Reagent
3.1.1 N,N-dimethyl acetamide (C4H9NO): chromatographically pure.
3.2 Standard product
Dichlorodifluoromethane (CCl2F2) (CAS No.: 75-71-8): with purity>99%.
3.3 Preparation of standard solution
3.3.1 Dichlorodifluoromethane standard stock solution (100 μg/mL) : accurately weigh 1 mg (accurate to 0.01 mg) dichlorodifluoromethane standard into 10 mL brown volumetric flask, dilute with N, N - dimethyl acetamide to the scale, and mix well, keep it at 4℃ with valid period of 1 year.
3.3.2 Dichlorodifluoromethane standard intermediate solution (10 μg/mL) : accurately transfer 1 mL dichlorodifluoromethane stock solution in 10 mL brown volumetric flask, dilute with N, N - dimethyl acetamide to the scale, and mix well, keep it at 4℃ with valid period of 6 months.
3.3.3 Dichlorodifluoromethane standard working solution (1 μg/mL) : accurately transfer 1 mL dichlorodifluoromethane intermediate solution into a 10 mL brown volumetric flask, dilute with N, N - dimethyl acetamide to the scale, and mix well, keep it at 4℃ with valid period of 3 months.
4 Instruments and Apparatus
4.1 Gas chromatograph (GC): equipped with hydrogen flame ionization detector (FID).
4.2 Electronic balance: with sensibility of 1 mg and 0.01 mg.
4.3 Thermostatic waterbath: with accuracy of 1℃.
4.4 Equilibration flask: 20 mL.
4.5 Air tight needle: 1.0 mL.
5 Analysis Steps
5.1 Specimen treatment
Cut the product of foamed polystyrene into 3 mm×3 mm fragments, sample by quartering, weigh 0.3 g (accurate to 0.001 g) and put them into the equilibration flask. Dissolve with 3 mL N, N-dimethyl acetamide, immediately cover with plug, gently shake well, balance in the 65℃ thermostatic waterbath for 15 min, take 1 mL gas into gas chromatograph for determination.
5.2 Reference conditions of instruments
a) Chromatographic column: 6% nitrile propyl phenyl and 94% dimethyl polysiloxane capillary chromatographic column with length of 30 m, inside diameter of 0.32 mm and film thickness of 0.18 μm, or equivalent;
b) Column temperature: maintain the initial temperature 50℃ for 5 min, then rise to 250℃ at a rate of 20℃/min and maintain 2.5 min;
c) Temperature of injection port: 250℃;
d) Detector temperature: 300℃;
e) Carrier gas: nitrogen, with purity≥99.999%; constant flow mode; flow rate of 1.0 mL/min;
f) Sample injection amount: 1.0 mL, split injection with split ratio of 1:1;
g) Make-up gas: nitrogen, 60 mL/min.
5.3 Plotting of standard curve
Add 3 mL N, N-dimethyl acetamide in five equilibration flasks respectively and cap the plugs, take 0 μL, 3 μL, 15 μL, 30 μL, 150 μL and 300 μL dichlorodifluoromethane standard working solution (1 μg/mL) with microinjector and inject into the equilibration flasks through rubber plug, gently shake well, and balance in 65℃ thermostatic waterbath for 15 min, i.e. the concentrations of standard curve are 0 ng/mL, 1 ng/mL, 5 ng/mL, 10 ng/mL, 50 ng/mL and 100 ng/mL. Inject 1 mL gas above solution respectively into the gas chromatograph, plot the standard curve with the content of dichlorodifluoromethane as x-axis and the peak area as y-axis. See Figure A.1 for the gas chromatogram of dichlorodifluoromethane standard solution.
5.4 Determination of specimen solution
Manually or automatically inject gas above solution containing 1 mL specimen into the gas chromatograph for determination and obtain the peak area, and obtain the content of dichlorodifluoromethane in specimen solution from the standard curve. Meanwhile, carry out blank test.
Foreword i
1 Scope
2 Principle
3 Reagents and Materials
4 Instruments and Apparatus
5 Analysis Steps
6 Expression of Analysis Results
7 Accuracy
8 Other
Annex A Gas Chromatogram of Dichlorodifluoromethane Standard Solution
