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This standard replaces "4.4 Ethylbenzene Compounds" of GB/T 5009.98-2003 Method for Analysis of Hygienic Standard of Unsaturated Polyester Resin and Glass Fibre Reinforced Plastics Used as Food Containers and Packaging Materials and "Chapter 6 Styrene, Ethylbenzene and Other Volatile Components" of GB/T 5009.59-2003 Method for Analysis of Hygienic Standard of Polystyrene Resin for Food Packaging.
The following main changes have been made with respect to "Chapter 6 Styrene, Ethylbenzene and Other Volatile Components" of GB/T 5009.59-2003:
——This standard is renamed as National Food Safety Standard - Food Contact Materials and Articles - Determination of Styrene and Ethylbenzene;
——Type of chromatographic column is modified;
——Determination method of insoluble sample is added.
National Food Safety Standard
Food Contact Materials and Articles
Determination of Styrene and Ethylbenzene
1 Scope
This standard specifies the gas chromatography method for the determination of styrene and ethylbenzene content in food contact materials and articles.
This standard is applicable to the determination of styrene and ethylbenzene in polystyrene products, unsaturated polyester resin and its glass fiber reinforced plastics products.
2 Principle
Inject the sample extracted by carbon disulfide into gas chromatography, separate styrene, ethyl benzene with internal standard n-dodecane and other components in the chromatographic column, detect with hydrogen flame ionization detector, and carry out quantative determination by internal standard method.
3 Reagents and Materials
3.1 Reagent
Carbon disulfide (CS2, CAS No.: 75-15-0): chromatographically pure.
3.2 Standard products
3.2.1 Styrene (C8H8, CAS No.: 100-42-5): with purity>99.5%, or reference material approved and awarded with reference material certificate by the State.
3.2.2 Ethylbenzene (C8H10, CAS No.: 100-41-4): with purity>99.5%, or reference material approved and awarded with reference material certificate by the State.
3.2.3 N-dodecane (C12H26, CAS No.: 112-40-3): with purity>99%, or reference material approved and awarded with reference material certificate by the State.
3.3 Preparation of standard solutions
3.3.1 Styrene standard stock solution
Weigh 200 mg styrene (accurate to 0.0001g), dissolve with carbon disulfide and scale the volume to 10 mL to prepare into the stock solution with the concentration of 20 mg/mL; the solution shall be kept in a dark place at 4℃, with valid period of a week.
3.3.2 Ethylbenzene standard stock solution
Weigh 200 mg ethylbenzene (accurate to 0.0001g), dissolve with carbon disulfide and scale the volume to 10 mL to prepare into the stock solution with the concentration of 20 mg/mL; the solution shall be kept in a dark place at 4℃, with valid period of a week.
3.3.3 Styrene - ethylbenzene intermediate solution
Pipet 0.25 mL styrene standard stock solution and 0.25 mL ethylbenzene standard stock solution with graduated pipette to a 10 mL volumetric flask with 5 mL carbon disulfide in advance, dilute with carbon disulfide and scale the volume to obtain styrene - ethyl benzene intermediate solution, in which the concentration of styrene and ethylbenzene is 500.0 μg/mL respectively. The storage conditions of the solution are same as 3.3.1.
3.3.4 N-dodecane internal standard stock solution
Weigh 250 mg n-dodecane (accurate to 0.0001g), dissolve with carbon disulfide and scale the volume to 10mL to prepare into the stock solution with the concentration of 25 mg/mL. The storage conditions of the solution are as specified in 3.3.1.
3.3.5 N-dodecane internal standard intermediate solution
Pipet 0.50 mL n-dodecane internal standard stock solution with graduated pipette to a 10mL volumetric flask containing 5 mL carbon disulfide in advance and scale the volume with carbon disulfide to prepare into the intermediate solution with the concentration of 1250 μg/mL. The storage conditions of the solution are as specified in 3.3.1.
3.3.6 Styrene, styrene and n-dodecane mixed standard working solution
Transfer 50 μL, 250 μL, 500 μL, 1.0 mL, 2.5 mL and 5.0 mL styrene - ethylbenzene intermediate solutions respectively into six 25 mL volumetric flasks containing 5 mL carbon disulfide with microinjector and graduated pipette, add 1.0 mL n-hexane internal standard intermediate solution in each volumetric flask, scale the volume with carbon disulfide and shake well to obtain the working solution. The concentrations of styrene/ethylbenzene are 1.0 μg/mL, 5.0 μg/mL, 10.0 μg/mL, 20.0 μg/mL , 50.0 μg/mL and 100.0 μg/mL respectively, and the internal standard concentration is 50 μg/mL. The storage conditions of the solution are as specified in 3.3.1.
4 Instruments and Apparatus
4.1 Gas chromatograph: equipped with hydrogen flame ionization detector (FID).
4.2 Analytical balance: with sensibility of 0.0001g.
4.3 Ultrasonic cleaner.
4.4 Freezing grinder.
4.5 Conical flask: 25 mL.
5 Analysis Steps
5.1 Treatments of specimens
As for specimen soluble in carbon disulfide, directly weigh them; as for specimen insoluble in carbon disulfide, weigh them after crushing them into fragments with particle size less than 1 mm×1 mm with freezing grinder, scissor or other cutting tools. The specimens cannot be heated or softened during cutting.
5.2 Preparation of specimen solutions
As for specimen soluble in carbon disulfide, weigh 0.5 g (accurate to 0.001 g) specimen and put into a 25 mL volumetric flask, transfer 10 mL carbon disulfide into the volumetric flask, and add 1.0 mL internal standard intermediate solution. Keep it still until specimen is dissolved, dilute it with carbon disulfide to the scale. As for specimen insoluble in carbon disulfide, weigh 0.5 g (accurate to 0.001 g) specimen and put into a 25 mL conical flask, and transfer 10 mL carbon disulfide into the conical flask. Extract with ultrasonic cleaner for 20 min after capping, and extract the supernatant into the 25 mL volumetric flask. Then, extract again with 10 mL carbon disulfide by the same method, and merge the two supernatant into 25 mL volumetric flask, add 1.0 mL internal standard intermediate solution and scale the volume. If the sample concentration exceeds the linear range, it needs to be re-extracted and properly diluted with carbon disulfide before the addition of the internal standard solution, so that the concentration is within the linear range. Prepare the blank extracting solution by the same method without addition of the specimen.
5.3 Preparation of blank solution
Adopt the identical analysis steps, reagents and consumption as specified in 5.2 except the specimen is not added.
5.4 Reference conditions of instruments
5.4.1 Chromatographic column: with stationary phase of polyethylene glycol, length of 30 m, inside diameter of 0.32 mm and film thickness of 0.5 μm.
5.4.2 Temperature of injection port: 250℃.
5.4.3 Column temperature: maintain the initial temperature 50℃ for 1 min, rise to 140℃ at a rate of 10℃/min, then rise to 220℃ at the rate of 20℃/min, and maintain for 10min.
5.4.4 Sample injection mode: split injection, with split ratio of 2:1.
5.4.5 Carrier gas: nitrogen, with purity>99.999%, and flow rate of 1.5 mL/min;
5.4.6 Detector: hydrogen flame ionization detector.
5.4.7 Injection volume: 1 μL.
5.4.8 Detector temperature: 300℃.
5.4.9 Hydrogen flow rate: 30 mL/min, with purity≥99.999%.
5.4.10 Air flow rate: 300 mL/min, with purity≥99.999%.
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 Standard Solutions
