National Food Safety Standard
Food Contact Materials and Articles
Determination of Heavy Metals in Food Simulants
食品安全國家標準 食品接觸材料及制品
食品模擬物中重金屬的測定
1 Scope
This standard specifies the determination method of heavy metals in food simulants (4% acetic acid).
Method I of this standard is applicable to the determination of heavy metals in food simulants (4% acetic acid) of food contact materials and articles.
Method II of this standard is applicable to the determination of heavy metals in food simulants (4% acetic acid) of food contact rubbers.
Method I Direct Colorimetry
2 Theory
React the heavy metal (calculated by lead) in test solution of food simulant obtained from migration test with sodium sulfide, form the yellowish-brown sulfide in acid solution, then compare its color with the color of lead standard solution.
3 Reagents and Materials
Note: unless otherwise specified, all reactants adopted for this method are analytically pure and water is Grade 2 water as specified in GB/T 6682.
3.1 Reactants
3.1.1 Sodium sulfide 9-hydrate (Na2S·9H2O).
3.1.2 Glycerol (C3H8O3).
3.1.3 Glacial acetic acid (CH3COOH).
3.1.4 Nitric acid (HNO3 with mass fraction of 60%).
3.2 Preparation of reagents
3.2.1 Nitric acid solution (with mass fraction of 10%): pipet 16.7mL of nitric acid (3.1.4) and dilute with water to 100mL.
3.2.2 Sodium sulfide solution: weigh 15.4g of sodium sulfide 9-hydrate (3.1.1), add 10mL of water, stir sufficiently with glass rod until it is dissolved, then add 30mL of glycerol (3.1.2), mix uniformly and keep sealed for preservation. The stability of this solution can be ensured for a month at room temperature.
3.2.3 Food simulant: 4% acetic acid solution (volume fraction). Put 40mL of glacial acetic acid (3.1.3) into a 1L volumetric flask, and dilute it with water to the scale.
3.3 Standards
Lead nitrate (Pb(NO3)2, >98%) or lead standard solution (with 1mg lead per milliliter) approved and awarded with reference material certificate by the nation.
3.4 Preparation of standard solutions
3.4.1 Lead standard stock solution: accurately weigh 0.1598g of lead nitrate (3.3.1, to the nearest 0.0001g), dissolve it in 10mL of nitric acid solution (3.2.1), transfer the solution into a 1,000mL volumetric flask, dilute it with water to the scale. 1mL of this solution is equivalent to 100μg of lead.
3.4.2 Lead standard application solution: pipet 10.0mL of lead standard stock solution (3.4.1) into a 100mL volumetric flask, and dilute it with water to the scale, then shake well; or pipet 1.0mL of lead standard solution (3.3) approved and awarded with reference material certificate by the nation into a 100mL volumetric flask, and dilute it with water to the scale, then shake well.
1mL of this solution is equivalent to 10μg of lead.
4 Apparatuses
4.1 Constant-temperature oven.
4.2 Volumetric flask: 100mL and 1,000mL.
4.3 Pipet: 10mL and 20mL.
4.4 Colorimetric tube: 50mL.
4.5 Measuring cylinder: 50mL.
4.6 Analytical balance: with a sensitivity of 0.0001g and 0.1g.
5 Analytical Procedures
5.1 Preparation of specimen
According to the requirements of "General Principle of Migration Test Pretreatment of Food Contact Materials and Their Products" (GB/T 5009.156) and national standards of corresponding products, take 4% acetic acid solution (3.2.3) as the specimen of food simulant to conduct migration test, and obtain the test solution of food simulant. Protect it from light in a refrigerator with 0℃~4℃.
5.2 Determination of specimen solution
Pipet 20mL of test solution (5.1) of food simulant obtained through migration test into a 50mL colorimetric tube, and dilute it with water to the scale; pipet 2mL of standard lead application solution (3.4.2) into a 50mL colorimetric tube, add 20mL of 4% acetic acid solution (3.2.3), and add water to the scale, then mix uniformly. Respectively add 2 drops of sodium sulfide solution (3.2.2) into these two solutions, mix uniformly and keep them still for 5min; take white color as the background, observe these two solutions from top or side face, and compare the color of test solution of simulant and standard solution.
6 Expression of Analysis Results
In the case that the color of specimen is darker than that of the standard solution, the migration volume (calculated by lead) of heavy metals in food contact materials and articles is larger than 1mg/L;
In the case that the color of specimen is lighter than that of the standard solution, the migration volume (calculated by lead) of heavy metals in food contact materials and articles is less than 1mg/L.
Method II Masking Interference Colorimetry
7 Theory
React the heavy metal (calculated by lead) in test solution of food simulant obtained from migration test with sodium sulfide, form the yellowish-brown sulfide in acid solution, then compare its color with that of lead standard solution.
8 Reagents and Materials
Unless otherwise specified, all reactants adopted for this method are analytically pure and water is Grade 2 water as specified in GB/T 6682.
8.1 Reactants
8.1.1 Sodium sulfide 9-hydrate (Na2S·9H2O).
8.1.2 Ammonium citrate (C6H17N3O7).
8.1.3 Potassium cyanide (KCN).
8.1.4 Ammonia water (NH3·H2O).
8.1.5 Glycerol (C3H8O3).
8.1.6 Glacial acetic acid (CH3COOH).
8.1.7 Nitric acid (HNO3, with mass fraction of 60%).
8.2 Preparation of reagents
8.2.1 Potassium cyanide solution (100g/L): weigh 10g (to the nearest 0.1g) of potassium cyanide (8.1.3) and dissolve it in water to 100mL.
8.2.2 Ammonium citrate solution (500g/L): weigh 50g (to the nearest 0.1g) of ammonium citrate (8.1.2) and dissolve it in water to 100mL.
8.2.3 Nitric acid solution (with a mass fraction of 10%): pipet 16.7mL of nitric acid (8.1.7) and dilute it with water to 100mL.
8.2.4 Sodium sulfide solution: weigh 15.4g of sodium sulfide 9-hydrate (8.1.1), dilute it with 10mL of water, stir sufficiently with glass rod until it is dissolved, then add 30mL of glycerol (8.1.5), mix uniformly and keep sealed for preservation. The stability of this solution can be ensured for a month at room temperature.
8.2.5 Food simulant: 4% acetic acid (volume fraction). Put 40mL of glacial acetic acid (8.1.6) into a 1L volumetric flask, and dilute it with water to the scale.
Foreword I
1 Scope
2 Theory
3 Reagents and Materials
4 Apparatuses
5 Analytical Procedures
6 Expression of Analysis Results
7 Theory
8 Reagents and Materials
9 Apparatuses
10 Analytical Procedures
11 Expression of Analysis Results
