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This standard replaces the determination method of aluminum in GB/T 5009.182-2003 Determination of Aluminum in Flour Products, GB/T 23374-2009 Determination of Aluminum in Foods - Inductively Coupled Plasma Mass Spectrometry, 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 Spectrometric Method and SN/T 2208-2008 Determination of Sodium, Magnesium, Aluminum, Calcium, Chromium, Iron, Nickel, Copper, Zinc, Arsenic, Strontium, Molybdenum, Cadmium, Lead, Mercury, Selenium in Aquatic Products - Microwave Digestion - ICP/MS Method.
The following main changes have been made with respect to GB/T 5009.182-2003 (the previous edition):
——The standard name is revised as National Food Safety Standard - Determination of Aluminum in Foods;
——Method I spectrophotometry is improved;
——Inductively coupled plasma mass spectrometry is added as Method II;
——Inductively coupled plasma emission spectrometry is added as Method III;
——Graphite furnace atomic absorption spectrometry is added as Method IV.
National Food Safety Standard
Determination of Aluminum in Foods
1 Scope
This standard specifies spectrophotometry, inductively coupled plasma mass spectrometry, inductively coupled plasma emission spectrometry and graphite furnace atomic absorption spectrometry for determination of aluminum content in foods.
In this standard, Method I is applicable to determination of aluminum in foods containing aluminum food additives while Method II, Method III and Method IV are applicable to determination of aluminum in foods.
Method I Spectrophotometry
2 Principle
After specimen treatment, in ethylenediamine-hydrochloric acid buffer solution (pH 6.7~7.0) with TritonX-100 and CPB, tervalent aluminum ion reacts with chrome azurol S to generate glaucous quaternionic micelle; determine absorbance value at wavelength of 620nm and compare with standard series for quantification.
3 Reagents and Materials
Unless otherwise specified, analytically-pure reagents and Class-III water (defined in GB/T 6682) are adopted.
3.1 Reagents
3.1.1 Nitric acid (HNO3): guaranteed reagent.
3.1.2 Sulfuric acid (H2SO4): guaranteed reagent.
3.1.3 Hydrochloric acid (HCl): guaranteed reagent.
3.1.4 Ammonia water (NH3·H2O): guaranteed reagent.
3.1.5 Absolute ethanol (C2H6O): guaranteed reagent.
3.1.6 p-nitrophenol (C6H5NO3).
3.1.7 Chrome azurol S (C23H13O9SCl2Na3).
3.1.8 Ethylenediamine (C2H8N2).
3.1.9 Octyl phenoxy poly ethoxy (TritonX-100).
3.1.10 Cetyl pyridine bromide (CPB,C21H38BrN).
3.1.11 Ascorbic acid (C6H8O6).
3.2 Preparation of reagents
3.2.1 Hydrochloric acid solution (1+1): measure 50mL hydrochloric acid and mix it uniformly with 50mL water.
3.2.2 Sulfuric acid solution (1%): pipet 1mL sulfuric acid, slowly add into 80mL water, dilute it with water to 100mL after cooling and mix uniformly.
3.2.3 p-nitrophenol ethanol solution (1g/L): weigh 0.1g p-nitrophenol, dissolve in 100mL absolute ethanol and mix uniformly.
3.2.4 Nitric acid solution (5%): measure 5mL nitric acid, scale the volume with water to 100mL and mix uniformly.
3.2.5 Nitric acid solution (2.5%): measure 2.5mL nitric acid, scale the volume with water to 100mL and mix uniformly.
3.2.6 Ammonia solution (1+1): measure 10mL ammonia water, add into 10mL water and mix uniformly.
3.2.7 Nitric acid solution (2+98): measure 2mL nitric acid and mix it uniformly with 98mL water.
3.2.8 Ethanol solution (1+1): measure 50mL absolute ethanol, dissolve in 50mL water and mix uniformly.
3.2.9 Chrome azurol S solution (1g/L): weigh 0.1g chrome azurol S, dissolve in 100mL ethanol solution (1+1) and mix uniformly.
3.2.10 TritonX-100 solution (3%): pipet 3mL TritonX-100, put into a 100mL volumetric flask, scale the volume with water to the scale and mix uniformly.
3.2.11 CPB solution (3g/L): weigh 0.3g CPB, dissolve in 15mL absolute ethanol, dilute with water to 100mL and mix uniformly.
3.2.12 Ethylenediamine solution (1+2): measure 10mL ethylenediamine, slowly add into 20mL water and mix uniformly.
3.2.13 Ethylenediamine-hydrochloric acid buffer solution (pH 6.7~7.0): measure 100mL ethylenediamine, slowly add into 200mL water along glass rod, then slowly add 190mL hydrochloric acid along glass rod after cooling, and mix uniformly; if pH>7.0 or pH <6.7, adjust the pH value respectively with hydrochloric acid solution (1+1) or ethylenediamine solution (1+2).
3.2.14 Ascorbic acid solution (10g/L): weigh 1g ascorbic acid, dissolve with water, scale the volume with water to 100mL and mix uniformly. Prepare immediately before use.
3.3 Standard product
Aluminum standard solution: 1000mg/L, or aluminum standard solution of certain concentration approved and awarded with reference material certificate by the State.
3.4 Preparation of standard solutions
3.4.1 Aluminum standard intermediate solution (100mg/L): accurately pipet 1.00mL aluminum standard solution (1000mg/L) into a 10mL volumetric flask, scale the volume with nitric acid solution (5%) to the scale and mix uniformly.
3.4.2 Aluminum standard working solution (1.00mg/L): accurately pipet 1.00mL aluminum standard intermediate solution (100mg/L) into a 100mL volumetric flask, dilute with nitric acid solution (5%) to the scale and mix uniformly.
4 Instruments and Apparatus
Note: all glass apparatus shall be soaked in nitric acid (1+5) at least overnight, flushed with tap water repeatedly, and finally washed clean with water before use.
4.1 Spectrophotometer.
4.2 Balance: with sensitivity of 1mg.
4.3 Adjustable temperature control electrothermal furnace or electric hot plate.
4.4 Acidometer (±0.1pH).
4.5 Thermostatic drying oven.
5 Analysis Steps
5.1 Preparation of specimen
Specimen shall be free from contamination in the process of sampling and preparation; appliances containing aluminum shall not be used.
Uniformly crush samples such as flour product, bean product, shrimp flavor slice and baked foods, take about 30g and put into 85℃ thermostatic drying oven for 4h drying.
5.2 Digestion of specimen
Weigh 0.2~3g (accurate to 0.001g) specimen or accurately transfer 0.500~5.00mL liquid specimen, put into a hard glass digestion tube or conical flask, add 10mL nitric acid and 0.5mL sulfuric acid, and heat in adjustable temperature control electrothermal furnace or on electric hot plate. Recommended conditions: heat at 100℃ for 1h, at 150℃ for 1h, at 180℃ for 2h, and then rise to 200℃; if it becomes brownish black, add nitric acid for digestion until white smoke appears at the tube opening and digestion solution becomes colorless and transparent or slightly yellow. Take out, cool, transfer and scale the volume with water into 50mL (V1) volumetric flask, mix uniformly for standby. Meanwhile, carry out reagent blank test.
5.3 Chromogenic reaction and colorimetric determination
Respectively pipet 1.00mL (V2) specimen digestion solution and blank solution into 25mL colorimetric cylinder with stopper, add water to 10mL scale. Additionally take 7 pieces of 25mL colorimetric cylinders with stopper, respectively add aluminum standard working solution 0mL, 0.500mL, 1.00mL, 2.00mL, 3.00mL, 4.00mL and 5.00mL (the aluminum mass in this series of standard solutions is respectively 0μg, 0.500μg, 1.00μg, 2.00μg, 3.00μg, 4.00μg and 5.00μg), and successively add 1mL sulfuric acid solution (1%) into each cylinder, then add water to 10mL scale.
Add 1 drop of p-nitrophenol ethanol solution (1g/L) into standard tube, specimen tube and reagent blank tube, mix uniformly, add ammonia solution (1+1) by drops until turning pale yellow, add nitric acid solution (2.5%) by drops until yellow just disappears, and add another 1mL; add 1mL ascorbic acid solution (10g/L) and mix uniformly, add 3mL chrome azurol S solution (1g/L) and mix uniformly, add 1mL Triton X-100 solution (3%), 3mL CPB solution (3g/L) and 3mL ethylenediamine-hydrochloric acid buffer solution; scale the volume with water to 25.0mL, mix uniformly and put for 40min.
Determine the absorbance value with blank solution as reference by 1cm cuvette at wavelength of 620nm. Plot the standard curve with the aluminum mass in standard series solutions as x-axis and the corresponding absorbance value as y-axis. Compare with standard curve for quantification according to the absorbance.
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 Heating Conditions of Pressure Tank Digestion
