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This standard replaces the methods for determination of nickel migration in GB/T 5009.81-2003 Method for Analysis of Hygienic Standard of Stainless Steel Food Containers and Table Wares and SN/T 2829-2011 Food Contact Materials and Articles - Metal Materials - Determination of Heavy Metal Content in Food Simulant - Inductively Coupled Plasma Atomic Emission Spectrometric Method.
The following main changes have been made with respect to the nickel determination method in GB/T 5009.81-2003:
——The standard name is revised as "National Food Safety Standard - Food Contact Materials and Articles - Determination of Nickel Migration";
——The inductively coupled plasma mass spectrometry method and inductively coupled plasma atomic emission spectrometric method are added.
National Food Safety Standard -
Food Contact Materials and Articles – Determination of Nickel Migration
1 Scope
This standard specifies the graphite furnace atomic absorption spectrometry method, inductively coupled plasma mass spectrometry method, inductively coupled plasma atomic emission spectrometric method and dimethylglyoxime colorimetry method for determination of nickel migration after the food contact materials and articles are immersed in food simulants.
This standard is applicable to determination of migration of nickel from food contact materials and articles.
Method I Graphite Furnace Atomic Absorption Spectrometry Method
2 Theory
Take the part of food contact materials and articles having been immersed in food simulants which is expected to contact with foodstuffs; the immersion solution is atomized by graphite furnace; the absorption value determined at 232.0 nm is proportional to the nickel content within certain concentration range; compare it with standard series for quantification.
3 Reagents and Materials
Unless otherwise specified, guaranteed reagents and Class-II water (defined in GB/T 6682) are adopted for the purpose of this method.
3.1 Reagents
3.1.1 Nitric acid (HNO3).
3.1.2 Ammonium dihydrogen phosphate (NH4H2PO4).
3.1.3 Reagents required for preparation of food simulants: in accordance with the requirements of GB 31601.1.
3.2 Preparation of reagents
3.2.1 Nitric acid solution (1+1): take 250mL of nitric acid and add it into 250mL of water; mix uniformly.
3.2.2 Nitric acid solution (5+95): take 50mL of nitric acid and add it into 950mL of water; mix uniformly.
3.2.3 Food simulants: prepare according to the requirements of GB 5009.156.
3.2.4 Ammonium dihydrogen phosphate solution (20g/L): weigh 2.0g of ammonium dihydrogen phosphate, dissolve it in water and scale the volume to 100mL.
3.3 Standard substance
Metallic nickel (Ni; CAS No.: 7440-02-0): purity ≥99.99%, or standard solution approved and awarded with reference material certificate by the state.
3.4 Preparation of standard solution
3.4.1 Nickel standard stock solution (1,000 mg/L): accurately weigh 1g of metallic nickel (to the nearest of 0.001g), add a small amount of nitric acid solution (1+1), heat until the nickel is fully dissolved, then transfer the solution into a 1,000mL volumetric flask, add water to the scale, and mix uniformly; or adopt standard solution approved and awarded with reference material certificate by the state and dilute it.
3.4.2 Nickel standard intermediate solution (10.0 mg/L): pipet 1.00 mL of nickel standard stock solution and put it into a 100mL volumetric flask, add nitric acid solution (5+95) to dilute to the scale, and mix uniformly.
3.4.3 Nickel standard working solution (1.00 mg/L): pipet 10.0 mL of nickel standard stock solution and put it into a 100mL volumetric flask, add nitric acid solution (5+95) to dilute to the scale, and mix uniformly.
3.4.4 Nickel standard series solutions: accurately pipet 0 mL, 0.500 mL, 1.00 mL, 2.00mL, 3.00 mL and 4.00 mL of nickel standard working solutions (1.00 mg/L) and pour them into 50mL volumetric flasks respectively, dilute them to the scale with corresponding food simulants, and mix uniformly; the concentrations are 0 μg/L, 10.0μg/L, 20.0 μg/L, 40.0 μg/L, 60.0 μg/L and 80.0μg/L respectively.
Note: the concentration and range of nickel in standard series solutions may be determined according to the sensitivity and linear range of the instruments as well as the actual nickel content in the sample solution; if the selected food simulants are neutral or alkaline, right amount of nitric acid shall be added to make the concentration of nitric acid in the solution be about 5% (volume fraction).
4 Instruments and Apparatus
Note: all the glassware shall be immersed in nitric acid solution (1+5) over night, and then washed with water for standby.
4.1 Atomic absorption spectrometer: equipped with graphite furnace atomizer and nickel hollow cathode lamp.
4.2 Analytical balance: with sensibility of 0.1mg.
5 Analysis Steps
5.1 Specimen pretreatment
Carry out migration test according to the intended use and service conditions of the to-be-tested sample with the migration test methods and conditions specified in GB 5009.156 and GB 31604.1; mix the immersion test solution uniformly and take a part of it for analysis; if the soak test solution is neutral or alkaline, add into right amount of nitric acid to make the concentration of nitric acid in the test solution be about 5% (volume fraction); carry out the specimen blank test at the same time.
5.2 Determination
5.2.1 Test conditions of instruments
See Table A.1 for the reference conditions of instruments.
5.2.2 Plotting of standard curve
Pipet 10μL of nickel standard series solutions respectively in sequence from the solution with lowest concentration to that with highest concentration and 5 μL of ammonium dihydrogen phosphate solution (20g/L) (optimum injection volume may be determined according to the adopted instrument) and inject them into the graphite furnace simultaneously; after they are atomized, determine the absorbance value, and plot the standard curve with the concentration of standard series as x-axis and the corresponding absorbance value as y-axis.
5.2.3 Specimen determination
Pipet 10 μL of sample solution and 5μL of ammonium dihydrogen phosphate solution (20g/L) under the same test conditions as that for standard solution determination (optimum injection volume may be determined according to the adopted instrument), inject them into graphite furnace simultaneously, after they are atomized, determine the absorbance value, and compare with standard series for quantification; meanwhile, test the specimen blank solution.
6 Expression of Analysis Results
Obtain the concentration of nickel in specimen solution from standard curve, deduct the blank value and calculate the migration according to GB 5009.156 to obtain the migration of nickel from food contact materials and articles; three significant figures shall be reserved for the calculation results.
7 Precision
The absolute difference of the results from two independent determinations under repeatability conditions shall not exceed 20% of the arithmetic mean value.
Foreword i
1 Scope
2 Theory
3 Reagents and Materials
4 Instruments and Apparatus
5 Analysis Steps
6 Expression of Analysis Results
7 Precision
8 Others
9 Theory
10 Reagents and Materials
11 Instruments and Apparatus
12 Analysis Steps
13 Expression of Analysis Results
14 Precision
15 Others
Annex A Reference Temperature Rise Procedures of Graphite Furnace Atomic absorption Spectrometer
