National food safety standard — Determination of nickel in foods
1 Scope
This standard specifies graphite furnace atomic absorption spectrometry, inductively coupled plasma mass spectrometry and inductively coupled plasma emission spectrometry for the determination of nickel in foods.
This standard is applicable to the determination of nickel in foods.
Method I Graphite furnace atomic absorption spectrometry
2 Principle
After digestion treatment, carry out graphite furnace atomization for the specimen and determine the absorbance at 232.0nm. Within a certain concentration range, the absorbance of nickel is proportional to the content of nickel, which is quantified by external standard method.
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 Palladium nitrate [Pd(NO3)2].
3.1.4 Ammonium dihydrogen phosphate (NH4H2PO4).
3.2 Reagent preparation
3.2.1 Nitric acid solution (5+95): measure 50mL of nitric acid, and pour it slowly into 950mL water and mix well.
3.2.2 Nitric acid solution (1+1): measure 500mL of nitric acid, and pour it slowly into 500mL water and mix well.
3.2.3 Nitric acid solution (1+5): measure 100mL of nitric acid, and pour it slowly into 500mL water and mix well.
3.2.4 Ammonium dihydrogen phosphate-palladium nitrate solution: weigh 0.02g of palladium nitrate, dissolve it with a small amount of nitric acid solution (1+1), and then add 2g of ammonium dihydrogen phosphate, after dissolution, dilute it with nitric acid solution (1+1) to 100mL, and mix well.
3.3 Standards
Metallic nickel (Ni; CAS No.: 7440-02-0): with 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 (000 mg/L): accurately weigh 1g (accurate to 1g) metallic nickel, add into 30mL of nitric acid solution (1+1), heat them until they are dissolved, transfer into a 1000mL volumetric flask, dilute with water to the scale and mix uniformly. Refrigerate it at 0℃ to 5℃ and it is valid for 6 months.
3.4.2 Nickel standard intermediate solution (10.0 mg/L): accurately pipette 1.00mL of nickel standard stock solution (000 mg/L) into a 100mL volumetric flask, dilute it with nitric acid solution (5+95) to the scale, and mix well. Refrigerate it at 0℃ to 5℃ and it is valid for 6 months.
3.4.3 Nickel standard working solution (1.00 g/L): accurately pipette 10.00mL of nickel standard intermediate solution (10.0 mg/L) into a 100mL volumetric flask, dilute it with nitric acid solution (5+95) to the scale, and mix well. Refrigerate it at 0℃ to 5℃ and it is valid for 6 months.
3.4.4 Nickel standard series solutions: respectively pipet 0mL, 0.25mL, 0.50mL, 1.00mL, 2.00mL and 2.50mL of nickel standard working solutions (1.00mg/L) into 100mL volumetric flasks, add nitric acid solution (5+95) to the scale and mix uniformly. The mass concentrations of this series of nickel standard solutions are 0μg/L, 2.50μg/L, 5.0μg/L, 10.0μg/L, 20.0μg/L and 25.0μg/L, respectively. Prepare fresh solution before use.
Note: The mass concentration of nickel in standard series solutions may be determined according to the sensitivity of apparatus, the actual nickel content in sample and the different apparatus models.
4 Apparatus and equipment
Note: All glasswares and polytetrafluoroethylene digestion inner tanks and inner covers shall be soaked in nitric acid solution (1+5) overnight, flushed with water repeatedly, and finally washed clean with water and dried.
4.1 Atomic absorption spectrometer: equipped with graphite furnace atomizer and nickel hollow cathode lamp.
4.2 Analytical balance, with a sensitivity of 0.1mg and 1mg.
4.3 Adjustable electric furnace or adjustable electric heating plate.
4.4 Microwave digestion system: with a polytetrafluoroethylene digestion inner tank.
4.5 Pressure digestion tank: with a polytetrafluoroethylene digestion inner tank.
4.6 Thermostatic drying oven.
4.7 Muffle furnace.
4.8 Crusher, tissue homogenizer.
Contents
Foreword
1 Scope
2 Principle
3 Reagents and materials
4 Apparatus and equipment
5 Analytical procedure
6 Expression of analysis results
7 Precision
8 Others
9 Detection limit and quantitation limit
Annex A Reference temperature programming for microwave digestion
Annex B Reference temperature programming for graphite furnace
