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This standard replaces the determination methods of lead in GB 5009.12-2010 National Food Safety Standard - Determination of Lead in Foods, GB/T 20380.3-2006 Starch and Derived Products - Heavy Metals Content - Part 3: Determination of Lead Content by Atomic Absorption Spectrometry with Electrothermal Atomization, GB/T 23870-2009 Determination of Pb in Propolis - Microwave Digestion-Graphic Furnace Atomic Absorption 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 1100-2006 Determination of Lead, Cadmium in Rice - Graphite Furnace Atomic Absorption Spectrometry and SN/T 2211-2008 Determination of Lead, Cadmium in Royal Jelly - Graphite Furnace Atomic Absorption Spectrometry.
The following main changes have been made with respect to GB 5009.12-2010 (the previous edition):
——Among pretreatment methods, wet digestion and pressure tank digestion are reserved, dry ashing and ammonium persulfate ashing method are deleted and microwave digestion is 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; dithizone colorimetry is reserved as Method IV;
——Inductively coupled plasma mass spectrometry is added as Method II;
——Hydride-atomic fluorescence spectrometry and single-sweep polarography are deleted;
——Temperature rise procedures of microwave digestion, reference conditions of instruments for graphite furnace atomic absorption spectrometry and reference conditions of instruments for flame atomic absorption spectrometry are added as annexes.
National Food Safety Standard
Determination of Lead in Foods
1 Scope
This standard specifies graphite furnace atomic absorption spectrometry, inductively coupled plasma mass spectrometry, flame atomic absorption spectrometry and dithizone colorimetry for determination of lead content in foods.
This standard is applicable to the determination of lead content in various foods.
Method I Graphite Furnace Atomic Absorption Spectrometry
2 Principle
After digestion treatment, carry out graphite furnace atomization for the specimen and determine the absorbance at 283.3nm. Within certain concentration range, lead absorbance value is in direct proportion to lead 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 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+9): measure 50mL nitric acid, slowly add into 450mL 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+9), 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
Lead nitrate [Pb(NO3)2, CAS No.: 10099-74-8]: with purity>99.99%, or lead standard solution of certain concentration approved and awarded with reference material certificate by the State.
3.4 Preparation of standard solutions
3.4.1 Lead standard stock solution (1000mg/L): accurately weigh 1.5985g (accurate to 0.0001g) lead nitrate, dissolve with a small amount of nitric acid solution (1+9), transfer into a 1000mL volumetric flask, add water to the scale and mix uniformly.
3.4.2 Lead standard intermediate solution (1.00mg/L): accurately pipet 1.00mL lead 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 Lead standard series solutions: accurately pipet 0mL, 0.500mL, 1.00mL, 2.00mL, 3.00mL and 4.00mL lead standard working solutions (1.00mg/L) into 100mL volumetric flasks respectively, add nitric acid solution (5+95) to the scale and mix uniformly. Mass concentrations of such lead standard series solutions are 0μg/L, 5.00μg/L, 10.0μg/L, 20.0μg/L, 30.0μg/L and 40.0μg/L respectively.
Note: mass concentration of lead in standard series solutions may be determined according to the sensitivity of instruments and the actual lead 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 lead hollow cathode lamp.
4.2 Analytical balance: with sensitivity 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.
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 bottle 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 0.500~5.00mL 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 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 0.500~3.00mL liquid specimen into a microwave digestion tank, add 5mL nitric acid, and digest the specimen according to the operation steps of microwave digestion, see Annex A for digestion conditions. After cooling, take out the digestion tank, and place it on 140~160℃ electric hot plate for digesting to about 1mL. 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
16 Principle
17 Reagents and Materials
18 Instruments and Apparatus
19 Analysis Steps
20 Expression of Analysis Results
21 Accuracy
22 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
