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This standard replaces the determination method of copper in GB/T 5009.13-2003 Determination of Copper in Foods, GB 5413.21-2010 National Food Safety Standard - Determination of Calcium, Iron, Zinc, Sodium, Potassium, Magnesium, Copper and Manganese in Foods for Infants and Young Children, Milk and Milk Products, GB/T 23375-2009 Determination of Copper, Iron, Zinc, Calcium, Magnesium and Phosphorus Content in Vegetables and Derived Products, GB/T 9695.22-2009 Meat and Meat Products - Determination of Copper Content, GB/T 14609-2008 Inspection of Grain and Oils - Determination of Copper, Iron, Manganese, Zinc, Calcium, Magnesium in Cereals and Derived Products - Flame Atomic Absorption Spectrometry, GB/T 18932.12-2002 Method for the Determination of Potassium，Sodium，Calcium，Magnesium，Zinc，Iron，Copper，Manganese，Chromium，Lead, Cadmium Contents in Honey - Atomic Absorption Spectrometry and NY/T 1201-2006 Determination of Copper, Iron and Zinc Content in Vegetables and Derived Products.
The following main changes have been made with respect to GB/T 5009.13-2003 (the previous edition):
——The standard name is revised as National Food Safety Standard - Determination of Copper in Foods;
——Pretreatment methods, e.g. wet digestion, pressure tank digestion and microwave digestion, are added;
——Graphite furnace atomic absorption spectrometry is reserved as Method I, with ammonium dihydrogen phosphate - palladium nitrate solution as matrix modifier; flame atomic absorption spectrometry is reserved as Method III; sodium diethyl dithiocarbamate colorimetry is deleted;
——Inductively coupled plasma mass spectrometry is added as Method III;
——Inductively coupled plasma emission spectrometry is added as Method IV;
——Reference conditions of instruments for temperature rise procedures of microwave digestion, graphite furnace atomic absorption spectrometry and flame atomic absorption spectrometry are added as annexes.
National Food Safety Standard
Determination of Copper in Foods
1 Scope
This standard specifies graphite furnace and flame atomic absorption spectrometry, inductively coupled plasma mass spectrometry and inductively coupled plasma emission spectrometry for the determination of copper content in foods.
This standard is applicable to the determination of copper content in various foods.
After digestion treatment, carry out graphite furnace atomization for the specimen and determine the absorbance at 324.8nm. Within certain concentration range, copper absorbance value is in direct proportion to copper 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 Ammonium dihydrogen phosphate (NH4H2PO4).
3.1.4 Palladium nitrate [Pd(NO3)2].
3.2 Preparation of regents
3.2.1 Nitric acid solution (5+95): measure 50mL nitric acid, slowly add into 950mL water and mix uniformly.
3.2.2 Nitric acid solution (1+1): measure 250mL nitric acid, slowly add into 250mL water and mix uniformly.
3.2.3 Ammonium dihydrogen phosphate - palladium nitrate solution: weigh 0.02g palladium nitrate, dissolve with a small amount of nitric acid solution (1+1), add 2g ammonium dihydrogen phosphate, scale the volume with nitric acid solution (5+95) to 100mL after dissolution, and mix uniformly.
3.3 Standard product
Blue copperas (CuSO4·5H2O, CAS No.: 7758-99-8): with purity>99.99%, or copper standard solution of certain concentration approved and awarded with reference material certificate by the State.
3.4 Preparation of standard solutions
3.4.1 Copper standard stock solution (1000mg/L): accurately weigh 3.9289g (accurate to 0.0001g) blue copperas, dissolve with a small amount of nitric acid solution (1+1), transfer into a 1000mL volumetric flask, add water to the scale and mix uniformly.
3.4.2 Copper standard intermediate solution (1.00mg/L): accurately pipet 1.00mL copper standard stock solution (1000mg/L) into a 1000mL volumetric flask, add nitric acid solution (5+95) to the scale and mix uniformly.
3.4.3 Copper standard series solutions: respectively pipet 0mL, 0.500mL, 1.00mL, 2.00mL, 3.00mL and 4.00mL copper standard intermediate solution (1.00mg/L) into 100mL volumetric flasks, add nitric acid solution (5+95) to the scale and mix uniformly. Mass concentrations of such standard series solutions are 0μg/L, 5.00μg/L, 10.0μg/L, 20.0μg/L, 30.0μg/L and 40.0μg/L respectively.
Note: the mass concentration of copper in standard series solutions may be determined according to the sensitivity of instrument and the actual copper content in the sample.
4 Instruments and Apparatus
Note: both the glassware and polytetrafluoroethylene digestion inner tank 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 copper 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 during the sampling and preparation process.
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 Pretreatment of specimen
5.2.1 Wet digestion
Weigh 0.2~3g (accurate to 0.001g) solid specimen or accurately transfer 0.500mL~5.00mL liquid specimen into a 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.
5.2.2 Microwave digestion
Weigh 0.2~0.8g (accurate to 0.001g) solid specimen or accurately transfer 0.500mL~3.00mL liquid specimen into a microwave digestion tank, add 5mL nitric acid, and digest the specimen according to the operation steps of microwave digestion; see Table A.1 for digestion conditions. After cooling, take out the digestion tank, and place it on 140~160℃ electric hot plate for digesting to about 1.0mL. After cooling down the digestion tank, transfer the digestion solution into a 10mL volumetric flask, wash the digestion tank with a small amount of water for 2~3 times, merge the washing solution into the volumetric flask, dilute with water to the scale and mix uniformly for standby. Meanwhile, carry out reagent blank test.
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 9 Principle 10 Reagents and Materials 11 Instruments and Apparatus 12 Analysis Steps 13 Expression of Analysis Results 14 Accuracy 15 Other Annex A Temperature Rise Procedures of Microwave Digestion Annex B Reference Conditions of Instruments for Graphite Furnace Atomic Absorption Spectrometry Annex C Reference Conditions of Instruments for Flame Atomic Absorption Spectrometry
