This standard specifies the method for determination of lead in foods.
This standard is applicable to the determination of lead in foods.
2 Normative References
The documents contain provisions which, through reference in this standard, constitute essential provisions of this standard. For dated references, only the dated edition of the normative document referred to applies. For undated references, the latest edition of the normative document (including all the amendments) referred to applies.
The samples shall be incinerated or digested in acid, and then shall be injected into the graphite furnace of atomic absorption spectrophotometer, the resonance line of 283.3 nm shall be absorbed after electrothermal atomization, and its absorption value is proportional to the lead content within a certain concentration range, and the absorption value shall be determined by comparing with the standard series.
4 Reagents and Materials
Unless otherwise specified, the reagents used in this method all shall be analytical pures, and the water shall be the Grade I water as specified in GB/T 6682.
4.1 Nitric acid: super grade pure.
4.2 Ammonium persulfate.
4.3 Hydrogen peroxide (30%).
4.4 Perchloric acid: super grade pure.
4.5 Nitric acid (1+1): Take 50mL of nitric acid and slowly add it into 50mL of water.
4.6 Nitric acid (0.5mol/L): Take 3.2mL of nitric acid and add it into 50mL water, and then dilute the solution up to 100mL.
4.7 Nitric acid (1 mol/L): Take 6.4mL of nitric acid and add it into 50mL water, and then dilute the solution up to 100mL.
4.8 Ammonium dihydrogen phosphate solution (20 g/L): Weigh off 2.0g of ammonium dihydrogen phosphate and dissolve it in water, and then dilute the solution up to 100mL.
4.9 Mixed acid: Nitric acid + perchloric acid (9+1). Take 9 parts of nitric acid and 1 part of perchloric acid, and mix them.
4.10 Standard lead stock solution: Accurately weigh off 1.000g of metallic lead (99.99%) and add a little nitric acid (4.5) in several times into it, heat and dissolve it, the gross volume shall not exceed 37mL, transfer it into a 1000mL measuring flask and add water into up to the scale. Blend the solution. This solution contains 1.0mg of lead per 1 milliliter.
4.11 Standard lead application solution: Absorb 1.0mL of the standard lead stock solution every time and put it into the 100mL measuring flask, and then add nitric acid (4.6) into the measuring flask till the liquid level reaches the scale. Herein, the standard lead stock solution is diluted in many times to the standard lead application solution that contains 10.0ng, 20.0ng, 40.0ng, 60.0ng and 80.0ng of lead per 1 milliliter respectively.
