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This standard replaces the determination methods of magnesium in GB/T 5009.90-2003 Determination of Iron, Magnesium and Manganese in Foods, GB/T 9695.21-2008 Meat and Meat Products - Determination of Magnesium, 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 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 82.19-1988 Determination of Calcium and Magnesium in Fruit Juice.
The following main changes have been made with respect to GB/T 5009.90-2003 (the previous edition):
——The standard name is revised as National Food Safety Standard Determination of Magnesium in Foods;
——Sample pretreatment method is revised as wet digestion, microwave digestion, dry ashing and pressure tank digestion;
——Flame atomic absorption spectrometry is reserved for determination of sample and Titrimetric Method is deleted;
——Inductively coupled plasma emission spectrometry is added as Method II;
——Inductively coupled plasma mass spectrometry is added as Method III.
National Food Safety Standard
Determination of Magnesium in Foods
1 Scope
This standard specifies the flame atomic absorption spectrometry, inductively coupled plasma emission spectrometry and inductively coupled plasma mass spectrometry for the determination of magnesium content in foods.
This standard is applicable to the determination of magnesium 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 285.2nm. Within certain concentration range, magnesium absorbance value is in direct proportion to magnesium 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 Hydrochloric acid (HCl).
3.2 Preparation of regents
3.2.1 Nitric acid solution (5+95): measure 50mL nitric acid, pour into 950mL water and mix uniformly.
3.2.2 Nitric acid solution (1+1): measure 250mL nitric acid, pour into 250mL water and mix uniformly.
3.2.3 Hydrochloric acid solution (1+1): measure 50mL hydrochloric acid, pour into 50mL water and mix uniformly.
3.3 Standard product
Magnesium metal (Mg, CAS No.: 7439-95-4) or magnesium oxide (MgO, CAS No.: 1309-48-4): with purity>99.99%, or standard magnesium solution of certain concentration approved and awarded with reference material certificate by the State.
3.4 Preparation of standard solutions
3.4.1 Magnesium standard stock solution (1000mg/L): accurately weigh 0.1g (accurate to 0.0001g) magnesium metal or 0.1658g (accurate to 0.0001g) magnesium oxide burnt to constant weight at 800℃±50℃, dissolve in 2.5mL hydrochloric acid solution (1+1) and a small amount of water, transfer into a 100mL volumetric flask, add water to the scale and mix uniformly.
3.4.2 Magnesium standard intermediate solution (10.0mg/L): accurately pipet 1.00mL magnesium standard stock solution (1000mg/L) in a 100mL volumetric flask, add nitric acid solution (5+95) to the scale and mix uniformly.
3.4.3 Magnesium standard series solutions: respectively pipet 0mL, 2.00mL, 4.00mL, 6.00mL, 8.00mL and 10.00mL magnesium standard intermediate solutions into 100mL volumetric flasks, add nitric acid solution (5+95) to the scale. Mass concentrations of such standard series solutions are 0mg/L, 0.200mg/L, 0.400mg/L, 0.600mg/L, 0.800mg/L and 1.00mg/L respectively.
Note: the mass concentration of magnesium in standard series solutions may be determined according to the sensitivity of instrument and the actual magnesium 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 magnesium 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 Thermostatic drying oven.
4.7 Pressure digestion tank: equipped with polytetrafluoroethylene digestion inner tank.
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 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 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 Temperature Rise Procedures of Microwave Digestion
