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This standard replaces the determination methods of zinc in GB/T 5009.14-2003 Determination of Zinc 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 9695.20-2008 Meat and Meat Products - Method for Determination of Zinc, GB/T 14609-2008 Inspection of Grain and Oils - Determination of Copper, Iron, Manganese, Zinc, Calcium, Magnesium in Cereals and Derived Products by Atomic Absorption and Flame Spectrophotometry, 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, 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 5009.14-2003 (the previous edition):
——The standard name is revised as National Food Safety Standard - Determination of Zinc in Foods;
——In pretreatment methods, dry ashing is retained, and wet digestion, pressure tank digestion and microwave digestion are added;
——Flame atomic absorption spectrometry is retained as Method I, and dithizone colorimetric method as Method IV;
——Inductively coupled plasma atomic emission spectrometry is added as Method II;
——Inductively coupled plasma mass spectrometry is added as Method III;
——Temperature rise procedures of microwave digestion and reference conditions of instruments for flame atomic absorption spectrometry are added as annexes.
National Food Safety Standard
Determination of Zinc in Foods
1 Scope
This standard specifies flame atomic absorption spectrometry, inductively coupled plasma emission spectrometry, inductively coupled plasma mass spectrometry and dithizone colorimetric method for determination of zinc content in foods.
This standard is applicable to determination of zinc content in various foods.
Method I Flame Atomic Absorption Spectrometry
2 Principle
After digestion treatment, carry out flame atomization for the specimen and determine the absorbance at 213.9nm. Within certain concentration range, zinc absorbance value is in direct proportion to zinc 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).
3.2 Preparation of reagents
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.
3.3 Standard product
Zinc oxide (ZnO, CAS No.: 1314-13-2): with purity>99.99%, or certain concentration of zinc standard solution approved and awarded with reference material certificate by the State.
3.4 Preparation of standard solutions
3.4.1 Zinc standard stock solution (1000mg/L): accurately weigh 1.2447g (accurate to 0.0001g) zinc oxide and add a small amount of nitric acid solution (1+1); heat to dissolve it, transfer it into a 1000mL volumetric flask after cooling; add water to the scale and mix uniformly.
3.4.2 Zinc standard intermediate solution (10.0mg/L): accurately pipet 1.00mL zinc standard stock solution (1000mg/L) into a 100mL volumetric flask, add nitric acid solution (5+95) to the scale and mix uniformly.
3.4.3 Zinc standard series solution: accurately pipet 0mL, 1.00mL, 2.00mL and 4.00mL, 8.00mL and 10.00mL zinc standard intermediate solution to 100mL volumetric flasks respectively, add nitric acid solution (5+95) to the scale and mix uniformly. Mass concentrations of such zinc standard series solutions are 0mg/L, 0.100mg/L, 0.200mg/L, 0.400mg/L, 0.800mg/L and 1.00mg/L respectively.
Note: mass concentration of zinc in standard series solutions may be determined according to the sensitivity of instruments and the actual zinc 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 flame atomizer and zinc 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
Grind and store the samples in plastic bottles after foreign substances are removed from them.
5.1.2 Such samples as vegetable, 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
Accurately weigh 0.2~3g (accurate to 0.001g) solid specimen or accurately transfer 0.500mL~5.00mL liquid specimen to 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 appears 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 25mL or 50mL 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 Result
7 Accuracy
8 Other
9 Principle
10 Reagents
11 Instruments and Apparatus
12 Analysis Steps
13 Expression of Analysis Result
14 Accuracy
15 Other
Annex A Temperature Rise Procedures of Microwave Digestion
Annex B Reference Conditions of Instruments for Flame Atomic Absorption Spectrometry
