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This standard replaces GB/T 23296.10-2009 Food Contact Materials - Polymer - Determination of Terephthalic Acid in Food Simulants - High Performance Liquid Chromatography and SN/T 2184-2008 Food Contact Materials - Polymer Materials - Determination of Terephthalic Acid in Food Simulants - HPLC.
The following changes have been made with respect to GB/T 23296.10-2009 and SN/T 2184-2008 (the previous editions):
——This standard is renamed as National Food Safety Standard - Food Contact Materials and Articles - Determination of Migration of Terephthalic Acid;
——Preparation of food simulant test solution is modified;
——The expression of analysis results is modified;
——The detection limit and the quantitation limit are modified.
National Food Safety Standard
Food Contact Materials and Articles
Determination of Migration of Terephthalic Acid
1 Scope
This standard specifies the determination method of migration of terephthalic acid in food contact materials and articles.
This standard is applicable to the determination of migration of terephthalic acid in food contact materials and articles.
2 Principle
Separate the terephthalic acid in food simulant with high performance liquid chromatography and detect with ultraviolet detector. For the water-based, acidic or alcoholic food simulant, directly inject the samples for determination; for the olive oil medium food simulant, inject the sample after the extraction with dilute sodium bicarbonate solution. With phthalic acid as internal standard, carry out the quantitative determination by internal standard method.
3 Reagents and Materials
Unless otherwise specified, analytically-pure reagents and Class-I water (defined in GB/T 6682) are adopted for the purpose of this method.
3.1 Reagents
3.1.1 Sodium acetate trihydrate (C2H3O2Na·3H2O).
3.1.2 Sodium bicarbonate (NaHCO3).
3.1.3 n-Heptane (n-C4H16).
3.1.4 Methanol (CH3OH): chromatographically pure.
3.1.5 Isopropanol (C3H8O).
3.1.6 Phosphoric acid (H3PO4).
3.1.7 Glacial acetic acid (CH3COOH).
3.1.8 Water-based, acidic, alcoholic and oil-based food simulants: the reagents used shall be in accordance with the requirements of GB 31604.1.
3.2 Preparation of reagents
3.2.1 Water-based, acidic, alcoholic and oil-based food simulants: prepare according to GB 5009.156.
3.2.2 1 g/L sodium bicarbonate solution: weigh 1 g (accurate to 0.1 g) sodium bicarbonate, dissolve with water and put into a 1 L volumetric flask.
3.2.3 Sodium acetate buffer solution (pH=3.6): weigh 25.0 g sodium acetate trihydrate, dissolve in 350 mL water, add 5.0 mL phosphoric acid, adjust the pH value with about 50 mL glacial acetic acid to 3.6, scale the volume with water to 500 mL.
3.2.4 50% acetic acid solution: measure 50 mL glacial acetic acid, put into a 100 mL volumetric flask and scale the volume with water.
3.3 Standard product
3.3.1 Terephthalic acid (C8H6O4, CAS No.: 100-21-0): with purity≥99%, or reference material approved and awarded with reference material certificate by the State.
3.3.2 Phthalic acid (C8H6O4, CAS No.: 88-99-3): with purity≥99%, or reference material approved and awarded with reference material certificate by the State.
3.4 Preparation of standard solutions
3.4.1 Terephthalic acid standard stock solution (500 mg/L): accurately weigh 50 mg (accurate to 0.1 mg) terephthalic acid standard product, dissolve with 90 mL methanol, heat the solution to 50℃, maintain for 1 h to make the terephthalic acid fully dissolved, cool the solution, transfer into a 100 mL volumetric flask and scale the volume with methanol. It is valid for 6 months.
3.4.2 Terephthalic acid standard intermediate solution: add 0 mL, 1.0 mL, 2.0 mL, 5.0 mL, 10.0 mL and 20.0 mL terephthalic acid standard stock solutions into six 25 mL volumetric flasks, add 5 mL phthalic acid internal standard stock solution respectively and scale the volume with methanol. The concentrations of terephthalic acid standard intermediate solutions are 0.0 mg/L, 20 mg/L, 40 mg/L, 100 mg/L, 200 mg/L and 400 mg/L respectively, while that of all internal standard phthalic acids is 200 mg/L. Such solution shall be prepared on the day.
3.4.3 Water-based, acidic or alcoholic food simulant medium standard working solution: transfer 2.0 mL terephthalic acid standard intermediate solution into six 50 mL volumetric flasks respectively, scale the volume with corresponding food simulants. Concentrations of terephthalic acid standard working solutions in water-based, acidic or alcoholic food simulants are 0.0 mg/L, 0.8 mg/L, 1.6 mg/L, 4.0 mg/L, 8.0 mg/L and 16.0 mg/L respectively, while that of all internal standards is 8.0 mg/L.
3.4.4 Olive oil medium standard working solution: weigh 50 g olive oil into six 250 mL separating funnels respectively, accurate transfer into 2.0 mL terephthalic acid standard intermediate solution, mix uniformly, add 50 mL n-heptane and mix uniformly. Add 20 mL sodium bicarbonate solution, fully oscillate for 1min and keep still for 15 min until layering. Collect the water phase at the lower layer into a 100 mL beaker, add 20 mL sodium bicarbonate solution and re-extract the oil phase at the upper layer. Shake well and keep still, collect the water phase at the lower layer into a beaker, merge the above two extracting solutions of water phase. Filter the extract by passing through C18 solid-phase extraction column by injector or vacuum pump (flow rate: 10 mL/min ~20 mL/min). Collect the filtrate in a 50 mL volumetric flask, add 1.0 mL acetic acid solution (50%) and scale the volume with water. Take 1 mL ~ 2 mL filtrate and filter with filter membrane. Concentrations of terephthalic acid standard working solutions are 0.0 mg/kg, 0.8 mg/kg, 1.6 mg/kg, 4.0 mg/kg, 8.0 mg/kg and 16.0 mg/kg, while that of all internal standards is 8.0 mg/kg.
3.4.5 Phthalic acid internal standard stock solution (1,000 mg/L): accurately weigh 0.1 g (accurate to 0.1 mg) phthalic acid standard product, dissolve with 10 mL isopropanol, transfer the solution to a 100 mL volumetric flask and scale the volume with isopropanol. It is valid for 6 months.
3.4.6 Phthalic acid internal standard intermediate solution (200 mg/L): take 5 mL phthalic acid internal standard stock solution, put into a 25 mL volumetric flask and scale the volume with methanol.
4 Instruments and Apparatus
4.1 High-performance liquid chromatograph: equipped with ultraviolet detector and 10 μL quantitative loop.
4.2 Analytical balance: with sensibility of 0.1 mg and 0.1 g.
4.3 pH meter.
4.4 C18 solid-phase extraction column: 400 mg octadecylsilane (ODS).
4.5 Water system micro-porous filter membrane: 0.45 μm.
5 Analysis Steps
5.1 Sample migration test
Carry out migration test in accordance with the requirements of GB 5009.156 and GB 31604.1 for the sample, and obtain the food simulant test solution. If the obtained food simulant test solution fails to be used for the next test immediately, it shall be kept in dark place in 4℃ refrigerator.
The food simulant test solution obtained shall be cooled or recovered to the ambient temperature before next test.
5.2 Preparation of test solutions
5.2.1 Preparation of water-based, acidic or alcoholic food simulant test solution
Transfer 50.0 mL water-based food simulant obtained from the migration test into a 100 mL conical flask with 2.0 mL phthalic acid internal standard intermediate solution already beforehand, mix uniformly, take 1 mL ~2 mL and filter with filter membrane for determination.
5.2.2 Preparation of olive oil simulant test solution
Weigh 50.0 g olive oil medium food simulant obtained from the migration test, put into a 250 mL separating funnel, add 2.0mL internal standard intermediate solution, mix uniformly, measure 50 mL n-heptane and put into the separating funnel. Operate the following steps according to 3.4.4 "add 20 mL sodium bicarbonate solution, ...., take 1 mL ~ 2 mL filtrate and filter with filter membrane" for determination of the solution.
5.3 Preparation of blank test solution
Treat the food simulants which have not contacted the food contact materials and articles according to the steps described in 5.2.
5.4 Determination
5.4.1 Reference conditions of liquid chromatographic determination
Reference conditions of liquid chromatographic determination are listed below:
a) Chromatographic column: C18 column with length of 250 mm, inside diameter of 4.6 mm and particle size of 5 μm, or equivalent;
b) Mobile phases: A: 150 mL sodium acetate buffer solution (3.2.5) + 750 mL water; B: methanol;
During the determination of the water-based, acidic or alcoholic simulant test solution, the mobile phase meets A+B=80+20 (volume ratio); during the determination of olive oil simulant test solution, the mobile phase meets A+B=85+15 (volume ratio);
c) Flow rate: 1.5 mL/min;
d) Column temperature: ambient temperature;
e) Injection volume: 10 μL;
f) Ultraviolet detector: with wavelength of 242 nm.
5.4.2 Plotting of standard work curve
Inject the standard working solution samples in sequence and determine according to the determination conditions specified in 5.4.1. Plot the standard work curve with the concentration of terephthalic acid in standard working solution as x-axis (mg/L or mg/kg) and the peak area ratio of terephthalic acid/phthalic acid as y-axis. See Annex A for chromatogram of standard solution.
5.4.3 Determination of test solutions
Inject the samples for blank solution and food simulant test solution in sequence, and subtract the blank value to obtain the peak area ratio of terephthalic acid/phthalic acid.
Foreword i
1 Scope
2 Principle
3 Reagents and Materials
4 Instruments and Apparatus
5 Analysis Steps
6 Expression of Analysis Results
7 Confirmation
8 Accuracy
9 Other
Annex A Chromatogram of Terephthalic Acid Standard Product
Annex B Reference Conditions for Confirmation by Liquid Chromatography-tandem Mass Spectrometry
Annex C Multiple Reaction Monitoring (MRM) Chromatogram of Terephthalic Acid
