Foreword
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This standard replaces GB 5009.12-2017 National food safety standard - Determination of lead in foods.
The following main changes have been made with respect to GB 5009.12-2017:
——the pretreatment method of samples to be desalted in “Method I Graphite furnace atomic absorption spectrometry” has been added;
——“Method IV Dithizone colorimetric method” has been deleted; and
——the limit of detection and limit of quantification in “Method I Graphite furnace atomic absorption spectrometry” have been modified.
National food safety standard -
Determination of lead in foods
1 Scope
This standard specifies the determination of lead in foods using methods of graphite furnace atomic absorption spectrometry, inductively coupled plasma mass spectrometry and flame atomic absorption spectrometry.
This standard is applicable to the determination of lead in foods.
Method I Graphite furnace atomic absorption spectrometry
2 Principle
Atomize the digested specimen in a graphite furnace, and determine the absorbance at 283.3nm. Within a certain concentration range, the absorbance of lead is proportional to the lead content, which is quantified by comparing with the standard series.
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 Perchloric acid (HClO4).
3.1.3 Ammonium dihydrogen phosphate (NH4H2PO4).
3.1.4 Palladium nitrate [Pd(NO3)2].
3.1.5 Ammonium acetate (CH3COONH4).
3.1.6 Sodium acetate (CH3COONa).
3.2 Preparation of reagents
3.2.1 Nitric acid solution (5+95): measure 50mL nitric acid, and pour it slowly into 950mL water and mix well.
3.2.2 Nitric acid solution (1+9): measure 50mL nitric acid, and pour it slowly into 450mL water and mix well.
3.2.3 Nitric acid solution (1+99): measure 10mL nitric acid, and pour it slowly into 990mL water and mix well.
3.2.4 Sodium acetate solution (2mol/L): weigh 164.0g sodium acetate, dissolve it in water, and dilute it to 1,000mL.
3.2.5 Ammonium acetate solution (1mol/L): weigh 77.1g ammonium acetate, dissolve it in water, and dilute it to 1,000mL.
3.2.6 Ammonium dihydrogen phosphate-palladium nitrate solution: weigh 0.02g palladium nitrate, dissolve it with a small amount of nitric acid solution (1+9), and then add 2g ammonium dihydrogen phosphate, after dissolution, dilute it with nitric acid solution (5+95) to 100mL, and mix well.
3.3 Reference material
Lead nitrate [Pb(NO3)2, CAS No.: 10099-74-8]: with purity >99.99%, or the lead standard solution certified by the state and issued with the reference material certificate.
3.4 Preparation of standard solutions
3.4.1 Lead standard stock solution (1,000mg/mL): accurately weigh 1.5985g (accurate to 0.0001g) lead nitrate, dissolve it with a small amount of nitric acid solution (1+9), then transfer it into a 1,000mL volumetric flask, dilute it with water to the scale, and mix well.
3.4.2 Lead standard intermediate solution (10.0mg/L): accurately pipette 1.00mL lead standard stock solution (1,000mg/L) into a 100mL volumetric flask, dilute it with nitric acid solution (5+95) to the scale, and mix well.
3.4.3 Lead standard working solution (1.00mg/L): accurately pipette 10.00mL lead standard intermediate solution (10.0mg/L) into a 100mL volumetric flask, dilute it with nitric acid solution (5+95) to the scale, and mix well.
3.4.4 Lead standard solution series: respectively pipette 0mL, 0.2mL, 0.5mL, 1.0mL, 2.0mL and 4.0mL lead standard working solution (1.00mg/L) into 100mL volumetric flasks, dilute them with nitric acid solution (5+95) to the scale, and mix well. The mass concentrations of the lead standard solution series are 0μg/L, 2.0μg/L, 5.0μg/L, 10.0μg/L, 20.0μg/L and 40.0μg/L respectively.
Note: The mass concentration of lead in the standard solution series and the concentration of nitric acid solution may be determined according to the instrument sensitivity, the actual lead content in the sample and different instrument models.
4 Instruments and equipment
Note: All glasswares and polytetrafluoroethylene digestion inner tanks shall be soaked in nitric acid solution (1+5) or (1+4) overnight, flushed with water repeatedly, and finally washed clean with water and dried.
4.1 Atomic absorption spectrometer: with graphite furnace atomizer and lead hollow cathode lamp.
4.2 Analytical balance: with sensitivities of 0.1mg and 1mg respectively.
4.3 Adjustable electric furnace or adjustable electric heating plate.
4.4 Microwave digestion system: with a polytetrafluoroethylene digestion inner tank.
4.5 Thermostatic drying oven.
4.6 Pressure digestion tank: with a polytetrafluoroethylene digestion inner tank.
4.7 Solid phase extraction column: with packing of iminodiacetic acid resin or equivalent (0.075mm-0.150mm, 0.5g, 1mL).
Foreword i
1 Scope
Method I Graphite furnace atomic absorption spectrometry
2 Principle
3 Reagents and materials
4 Instruments and equipment
5 Analysis steps
6 Expression of analysis results
7 Precision
8 Others
Method II Inductively coupled plasma/mass spectrometry
Method III Flame atomic absorption spectrometry
9 Principle
10 Reagents and materials
11 Instruments and equipment
12 Analysis steps
13 Expression of analysis results
14 Precision
15 Others
Annex A Temperature programming for microwave digestion
Annex B Operation steps for desalting samples
Annex C Reference conditions for graphite furnace atomic absorption spectrometer
Annex D Reference conditions for flame atomic absorption spectrometer
