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This standard replaces the determination methods of potassium and sodium in GB/T 5009.91-2003 Determination of Potassium and Sodium in Foods, GB/T 15402-1994 Fruits, Vegetables and Derived Products - Determination of Sodium and Potassium, NY 82.18-1988 Determination of Potassium and Sodium in Fruit Juice, 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 18932.11-2002 Method for Determination of Potassium, Phosphorus, Iron, Calcium, Zinc, aluminum, Sodium, Magnesium, Boron, Manganese, Copper, Barium, Titanium, Vanadium, Nickel, Cobalt, Chromium Contents in Honey - Inductively Coupled Plasma Atomic Emission 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 1653-2008 Determination for Mineral Elements in Vegetables, Fruits and Derived Products by ICP-AES Method.
The following main changes have been made with respect to above standards:
——The standard name is revised as National Standard of Food Safety - Determination of Potassium and Sodium in Foods;
——Flame atomic absorption spectrometry is revised as Method I, flame atomic emission spectrometry as Method II, inductively coupled plasma emission spectrometry as Method III and inductively coupled plasma mass spectrometry as Method IV;
——The contents in preparation of specimen are modified;
——The contents in digestion of specimen are modified;
——The detection limit and quantitation limit of method are added;
——Annex is added.
National Standard of Food Safety
Determination of Potassium and Sodium in Foods
1 Scope
This standard specifies flame atomic absorption spectrometry, flame atomic emission spectrometry, inductively coupled plasma emission spectrometry and inductively coupled plasma mass spectrometry for the determination of potassium and sodium in foods.
This standard is applicable to the determination of potassium and sodium in foods.
Method I Flame Atomic Absorption Spectrometry
2 Principle
Inject the specimen into atomic absorption spectrometer after digestion treatment, potassium and sodium absorb 766.5nm and 589.0nm resonance line respectively after flame atomization, within certain concentration range, the absorption value is in direct proportion to contents of potassium and sodium 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 Cesium chloride (CsCl).
3.2 Preparation of reagents
3.2.1 Mixed acid [perchloric acid + nitric acid (1+9)]: measure 100mL perchloric acid, slowly add into 900mL nitric acid and mix uniformly.
3.2.2 Nitric acid solution (1+99): measure 10mL nitric acid, slowly add into 990mL water and mix uniformly.
3.2.3 Cesium chloride solution (50g/L): dissolve 5.0g cesium chloride in water, dilute with water to 100mL.
3.3 Standard products
3.3.1 Potassium chloride standard product (KCl): purity greater than 99.99%.
3.3.2 Sodium chloride standard product (NaCl): purity greater than 99.99%.
3.4 Preparation of standard solutions
3.4.1 Potassium and sodium standard stock solutions (1000mg/L): dry potassium chloride and sodium chloride in drying oven with temperature 110~120℃ for 2h. Accurately weigh 1.9068g potassium chloride or 2.5421g sodium chloride, dissolve in water and transfer into 1000mL volumetric flasks respectively, dilute to the scale, mix uniformly, store in polyethylene bottle and preserve it at 4℃, or use the standard solution approved and awarded with reference material certificate by the State.
3.4.2 Potassium and sodium standard working solutions (100mg/L): accurately pipet 10.0mL potassium or sodium standard stock solution into a 100mL volumetric flask, dilute with water to the scale, store in polyethylene bottle and preserve it at 4℃.
3.4.3 Potassium and sodium standard series working solutions: accurately pipet 0mL, 0.1mL, 0.5mL, 1.0mL, 2.0mL and 4.0mL potassium standard working solutions into 100mL volumetric flasks respectively, add 4mL cesium chloride solution, dilute with water to the scale and mix uniformly. Mass concentrations of potassium in such standard series working solutions are 0mg/L, 0.100mg/L, 0.500mg/L, 1.00mg/L, 2.00mg/L and 4.00mg/L respectively, the concentration range of standard solution may be properly adjusted according to the potassium concentration in actual sample solution. Accurately pipet 0mL, 0.5mL, 1.0mL, 2.0mL, 3.0mL and 4.0mL sodium standard working solution into 100mL volumetric flasks respectively, add 4mL cesium chloride solution, dilute with water to the scale and mix uniformly. Mass concentrations of sodium in such standard series working solutions are 0mg/L, 0.500mg/L, 1.00mg/L, 2.00mg/L, 3.00mg/L and 4.00mg/L respectively, the concentration range of standard solution may be properly adjusted according to the sodium concentration in actual sample solution.
4 Instruments and Apparatus
4.1 Atomic absorption spectrometer: equipped with flame atomizer and hollow cathode lamp of potassium and sodium.
4.2 Analytical balance: with sensibility of 1mg and 0.1mg.
4.3 Steel cylinder acetylene gas and air compressor for analysis.
4.4 Sample grinding apparatus: homogenizer and high speed grinder.
4.5 Muffle furnace.
4.6 Adjustable temperature control electric hot plate.
4.7 Adjustable temperature control electrothermal furnace.
4.8 Microwave digestion system: equipped with polytetrafluoroethylene digestion inner tank.
4.9 Thermostatic drying oven.
4.10 Pressure digestion tank: equipped with polytetrafluoroethylene digestion inner tank.
5 Analysis Steps
5.1 Preparation of specimen
5.1.1 Solid samples
5.1.1.1 Dry samples
Take the edible parts of the samples with low moisture content, such as bean, grain, fungi, tea, dried fruit and bakery products, and crush them uniformly with high speed grinder if necessary; shake well solid dairy products and such powder samples with uniform shape as albumen powder and flour.
5.1.1.2 Fresh samples
Clean the samples with high moisture content, such as vegetables, fruits and aquatic products, dry them in the air if necessary, take the edible parts and homogenize uniformly; as for meat and eggs, take the edible parts and homogenize uniformly.
5.1.1.3 Quick-frozen and canned foods
As for the unfrozen samples of quick-frozen and canned foods, take the edible parts and homogenize uniformly.
5.1.2 Liquid samples
Shake well such samples as soft drink and flavorings.
5.1.3 Semisolid samples
Mix uniformly.
5.2 Digestion of specimen
5.2.1 Microwave digestion method
Weigh 0.2~0.5g (accurate to 0.001g) specimen in a microwave digestion inner tank, heat the samples containing ethanol or carbon dioxide on electric hot plate at low temperature to remove ethanol or carbon dioxide, add 5~10mL nitric acid, cover it and place for 1h or overnight, tighten the outer tank, put into microwave digestion system for digestion (see Table A.1 for the digestion conditions). Take out the inner tank after cooling, put on adjustable temperature control electrothermal furnace, digest to nearly dry at 120~140℃, scale the volume with water to 25mL or 50mL and mix uniformly for standby. Meanwhile, carry out blank test.
Foreword i
1 Scope
2 Principle
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 Reference Conditions of Sample Determination
