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This standard replaces GB/T 5009.138-2003 Determination of Nickel in Foods.
The following main changes have been made with respect to GB/T 5009.138-2003 (the previous edition):
——The standard name is revised as National Food Safety Standard - Determination of Nickel in Foods;
——The contents in pretreatment of sample are revised, microwave digestion method and dry ashing are added;
——The determination conditions of graphite furnace atomic absorption spectrometry are optimized and matrix modifier is added;
——The quantitation limit of graphite furnace atomic absorption spectrometry is added;
——Method II colorimetry is deleted.
National Food Safety Standard
Determination of Nickel in Foods
1 Scope
This standard specifies the graphite furnace atomic absorption spectrometry for determination of nickel content in foods.
This standard is applicable to determination of nickel content in various foods.
2 Principle
After digestion treatment, carry out graphite furnace atomization for the specimen and determine the absorbance at 232.0nm. Within certain concentration range, nickel absorbance value is in direct proportion to nickel content and is compared 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 Perchloric acid (HClO4).
3.1.3 Palladium nitrate [Pd(NO3)2].
3.1.4 Ammonium dihydrogen phosphate (NH4H2PO4).
3.2 Preparation of reagents
3.2.1 Nitric acid solution (0.5mol/L): pipet 3.2mL nitric acid, dilute with water to 100mL and mix uniformly.
3.2.2 Nitric acid solution (1+1): measure 500mL nitric acid and mix uniformly with 500mL water.
3.2.3 Ammonium dihydrogen phosphate - palladium nitrate solution: weigh 0.02g palladium nitrate, add a small amount of nitric acid solution (1+1) for several times to dissolve it, add 2g ammonium dihydrogen phosphate again, scale the volume to 100mL with nitric acid solution (1+1) and mix uniformly.
3.3 Standard product
Nickel metal (Ni, CAS No.: 7440-02-0): purity>99.99%, or standard nickel solution with certain concentration approved and awarded with reference material certificate by the State.
3.4 Preparation of standard solutions
3.4.1 Nickel standard stock solution (1000mg/L): accurately weigh 1g (accurate to 0.0001g) metallic nickel, add into 30mL 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.
3.4.2 Nickel standard intermediate solution (1.00mg/L): accurately pipet 0.1mL nickel standard stock solution (1000mg/L) into a 100mL volumetric flask, scale the volume to the scale with nitric acid solution (0.5mol/L) and mix uniformly.
3.4.3 Nickel standard series solutions: accurately pipet 0mL, 0.500mL, 1.00mL, 2.00mL, 4.00mL and 5.00mL nickel standard intermediate solutions into 100mL volumetric flasks respectively, dilute to the scale with nitric acid solution (0.5mol/L) and mix uniformly. Mass concentrations of such nickel standard series solutions are 0μg/L, 5.00μg/L, 10.0μg/L, 20.0μg/L, 40.0μg/L and 50.0μg/L respectively.
Note: mass concentration of nickel in standard series solutions may be determined according to the sensitivity of instruments and the actual nickel content in the sample.
4 Instruments and Apparatus
Note: all glassware and polytetrafluoroethylene digestion inner tanks shall be soaked in nitric acid solution (1+5) overnight, flushed with tap water repeatedly and finally washed clean with water.
4.1 Atomic absorption spectrometer: equipped with graphite furnace atomizer and nickel hollow cathode lamp.
4.2 Analytical balance: with sensibility of 0.1mg and 1mg.
4.3 Adjustable electrothermal furnace.
4.4 Adjustable electric hot plate.
4.5 Microwave digestion system: equipped with polytetrafluoroethylene digestion inner tank.
4.6 Pressure digestion tank: equipped with polytetrafluoroethylene digestion inner tank.
4.7 Thermostatic drying oven.
4.8 Muffle furnace.
5 Analysis Steps
5.1 Preparation of specimen
Note: specimen shall be free from contamination in the process of sampling and preparation.
5.1.1 Grain and bean samples
Crush and store the samples in plastic bottles after foreign substances are removed from them.
5.1.2 Such samples as vegetables, fruits, fish and meat
Clean the samples with water, dry them in the air, take the edible parts to make into homogenate and store them in plastic bottles.
5.1.3 Such liquid samples as beverage, wine, vinegar, soy sauce, edible vegetable oil and liquid milk
Shake the samples well.
5.2 Digestion of specimen
5.2.1 Wet digestion
Weigh 0.2~3g (accurate to 0.001g) solid specimen or accurately transfer 0.500~5.00mL liquid specimen into the graduated digestion tube, add 10mL nitric acid and 0.5mL perchloric acid, digest on adjustable electrothermal furnace (reference conditions: 120℃/0.5~1h, rising to 180℃/2~4h and rising to 200~220℃). If the digestion solution becomes brown, add a small amount of nitric acid again, digest until white smoke appears; when the digestion solution becomes colorless and transparent or slightly yellow, take out the digestion tube, cool, scale the volume with water to 10mL and mix uniformly for standby. Meanwhile, carry out reagent blank test. Alternatively, adopt a conical flask, put on adjustable electric hot plate and carry out wet digestion according to the above-mentioned operation methods.
Foreword i
1 Scope
2 Principle
3 Reagents and Materials
4 Instruments and Apparatus
5 Analysis Steps
6 Expression of Analysis Results
7 Accuracy
8 Other
Annex A Suggested Temperature Rise Procedures for Microwave Digestion
Annex B Suggested Temperature Rise Procedures for Graphite Furnace
