Determination of the contents of calcium，copper，iron，magnesium，manganese，potassium, sodium and zinc in feeds-Method using atomic absorption spectrometry
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This standard is drafted in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 13885-2003 Animal Feeding Stuffs — Determination of the Contents of Calcium, Copper, Iron, Magnesium, Manganese, Potassium, Sodium and Zinc — Method Using Atomic Absorption Spectrometry in whole.
In addition to a number of editorial changes, the following technical deviations have been made with respect to the GB/T 13885-2003:
— GB/T 6682-1992 is replaced with GB/T 6682 (see 4.1);
— The formula for result calculation is added (see Clause 9);
— 5.5 is deleted, and 5.6 to 5.9 are modified to 5.5 to 5.8.
This standard has been redrafted and modified adoption of International Standard ISO 6869:2000 Animal Feeding Stuffs — Determination of the Contents of Calcium, Copper, Iron, Magnesium, Manganese, Potassium, Sodium and Zinc — Method Using Atomic Absorption Spectrometry.
The standard is changed largely from ISO 6869:2000 in structure; a list of the clauses in this standard and the equivalent clauses in the International Standard ISO 6869:2000 is given in the informative Annex A.
There are technical deviations between this standard and the International Standard ISO 6869:2000, and such deviations have been marked by perpendicular single line (|) in the outer side page margin of the corresponding clauses; a complete list of technical deviations, together with their justifications, is given in Annex B.
For the purposes of this standard, the following editorial changes have also been made:
— Standard title is changed to Determination of the Contents of Calcium, Copper, Iron, Magnesium, Manganese, Potassium, Sodium and Zinc in Feeds — Method Using Atomic Absorption Spectrometry.
— The notes of 8.3, 8.6.2, 8.6.3, 8.7.2 and 8.7.3 are added.
This standard is under the jurisdiction of National Technical Committee 76 on Feed Industry of Standardization Administration of China (SAC/TC 76).
The previous editions of this standard are as follows:
— GB/T 13885-1992, GB/T 13885-2003.
Determination of the Contents of Calcium, Copper, Iron, Magnesium, Manganese, Potassium, Sodium and Zinc in Feeds — Method Using Atomic Absorption Spectrometry
1 Scope
This standard specifies an atomic absorption spectrometric method for the determination of the contents of calcium (Ca), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), potassium (K), sodium (Na) and zinc (Zn) in animal feeding stuffs.
This standard is applicable to the determination of the contents of calcium (Ca), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), potassium (K), sodium (Na) and zinc (Zn) in compound feeds, concentrated feeds, concentrate supplements, additive premixes and feed raw materials.
The limit of determination for the elements concerned is as follows:
K and Na: 500 mg/kg;
Ca and Mg: 50 mg/kg;
Cu, Fe, Mn and Zn: 5 mg/kg.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 6682 Water for Analytical Laboratory Use — Specification and Test Methods (GB/T 6682-2008, ISO 3696:1987, MOD)
GB/T 14699.1 Animal Feeding Stuffs — Sampling (GB/T 14699.12005, ISO 6497:2002, IDT)
GB/T 20195 Animal Feeding Stuffs — Preparation of Test Samples (GB/T 20195-2006, ISO 6498:1998, IDT)
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3 Principle
A test portion is dissolved in hydrochloric acid, if necessary after ashing in a muffle furnace at (550 ± 15)°C. Any silica compounds present are removed by precipitation and filtration. The precipitate is dissolved in hydrochloric acid and diluted to the desired volume, then aspirated into the air-acetylene flame of the atomic absorption spectrometer. The absorbance of each element is measured by comparison with the absorbance of calibration solutions for the same element.
4 Reagents and Materials
Unless otherwise specified, analytical reagents that conform to relevant national standard shall be used for analysis.
4.1 Water, GB/T 6682, grade 3.
4.2 Concentrated hydrochloric acid (HCl).
4.3 Hydrochloric acid solution, 6 mol/L: Hydrochloric acid + water =1+1.
4.4 Hydrochloric acid solution, 0.6 mol/L: Hydrochloric acid + water =5+100.
4.5 Lanthanum nitrate solution: Dissolve 133 g of La(NO3)3·6H2O in 1 litre of water. Another lanthanum salt may be used if the lanthanum content of the prepared solution is the same.
4.6 Caesium chloride solution: Dissolve 100 g of caesium chloride (CsCl) in 1 litre of water. Another caesium salt may be used if the caesium content of the obtained solution is the same.
4.7 Stock solution of Cu, Fe, Mn and Zn: Mix 1 00 mL of water and 1 25 mL of concentrated hydrochloric acid (4.2) in a 1 litre volumetric flask. Weigh out the following in a volumetric flask and scale the volume with water:
— 392.9 mg of copper(II) sulfate pentahydrate (CuSO4·5H2O);
— 702.2 mg of ammonium iron(II) sulfate hexahydrate [(NH4)2SO4·FeSO4·6H2O];
— 307.7 mg of manganese sulfate monohydrate (MnSO4·H2O);
— 439.8 mg of zinc sulfate heptahydrate (ZnSO4·7H2O).
The contents of Cu, Fe, Mn and Zn of this stock solution are each 100 μg/mL.
Note: Ready-prepared commercially available solutions may be used.
4.8 Standard solution of Cu, Fe, Mn and Zn: Dilute 20.0 mL of the stock solution (4.7) with water to 100 mL in a volumetric flask. The contents of Cu, Fe, Mn and Zn of this solution are each 20 μg/mL. Prepare the solution fresh on the day of use.
4.9 Stock solution of Ca, K, Mg and Na: Weigh out the following in a 1 litre volumetric flask:
— 1.907 g of potassium chloride (KCl);
— 2.028 g of magnesium sulfate heptahydrate (MgSO4·7H2O);
— 2.542 g of sodium chloride (NaCl).
Add 50 mL of hydrochloric acid (4.3) to a beaker. Weigh into the beaker 2.497 g of calcium carbonate (CaCO3).
Caution: Beware of the development of carbon dioxide.
Boil for 5 min on an electric hot plate. Cool and transfer the solution to the volumetric flask containing the weighed salts of K, Mg and Na. Dissolve the salts and dilute to the mark with dilute hydrochloric acid (4.4). The contents of Ca, K and Na of this solution are each 1 mg/ml; the content of Mg of the solution is 200 μg/mL.
Note: Ready-prepared commercially available solutions may be used.
4.10 Standard solution of Ca, K, Mg and Na: Dilute 25.0 mL of stock solution (4.9) with hydrochloric acid (4.4) to 250 mL in a volumetric flask. The contents of Ca, K and Na of this solution are each 100 μg/mL; the content of Mg of the solution is 20 μg/mL. Prepare the solution fresh in the week of use and store it in a polyethylene bottle.
4.11 Lanthanum/caesium blank solution: Add 5 mL of lanthanum nitrate solution, 5 mL of caesium chloride solution and 5 mL of hydrochloric acid (4.3) to a 100 mL volumetric flask. Dilute to the mark with water.
5 Apparatus
Rinse all volumetric ware, including the pipettes used for preparing calibration solutions, with hydrochloric acid (4.4) before use. If dedicated incineration dishes and glassware are used, it is not necessary to boil with hydrochloric acid each time before use. Usual laboratory apparatus and, in particular, the following.
5.1 Analytical balance, capable of weighing to the nearest 0.1 mg.
5.2 Incineration dishes of platinum, quartz or porcelain, free from potassium and sodium, with a smooth unetched inner surface, upper internal diameter 4 cm to 6 cm, lower internal diameter 2 cm to 2.5 cm, and a height of about 5 cm. Before use, boil with hydrochloric acid (4.3).
5.3 Glassware of hard borosilicate glass. Before use, boil with hydrochloric acid (4.3) and rinse with water.
5.4 Electric hot plate.
5.5 Electric muffle furnace, capable of being maintained at (550 ± 15)°C.
5.6 Atomic absorption spectrometer, suitable for measuring at the wavelengths specified in 8.6.1 and 8.7.1, provided with an air-acetylene flame and a facility for correction for, or measurement of, background absorption.
5.7 Hollow cathode lamps or electrode-less discharge lamps, for the determination of Ca, Cu, Fe, K, Mg, Mn, Na or Zn.
5.8 Filter paper which does not release minerals.
6 Sampling
Sampling is not part of the method specified in this standard. A recommended sampling method is given in GB/T 14699.1
It is important that the laboratory receive a sample which is truly representative and has not been damaged or changed during transport or storage. Store the sample so that deterioration and other changes in composition are prevented.
7 Preparation of Test Sample
Prepare the test sample in accordance with GB/T 20195. The particle size of the sample shall pass through 0.45mm analysis screen.
8 Analytical Procedure
8.1 Detection of presence of organic matter
Heat a spatula with some test sample in a flame. If the test sample melts without smoke, little organic matter is present. If the test sample changes in colour and melting does not occur, the test sample contains organic matter.
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8.2 Test portion
Depending on the expected content, weigh 1 g to 5 g of the prepared test sample, to the nearest 1 mg, into an incineration dish. If the test sample contains organic matter, proceed in accordance with 8.3. If the test sample contains little or no organic matter, proceed in accordance with 8.4.
8.3 Dry ashing
Heat the incineration dish on a electric hot plate until the test portion has been completely carbonized. Avoid burning the test portion. Transfer the dish to the muffle furnace which has already been at a temperature of 550 °C for 1 5 min. Ash the sample for 3 h at this temperature. Allow the sample to cool down then moisten the contents of the dish with 2 mL of water. If many carbon particles are present, dry the dish over the electric hot plate slowly and carefully. Ash for another 2 h in the muffle furnace set at 550 °C. Allow to cool down then add 2 mL of water.
Note: Silicone compounds may affect the ashing effect of the compound premixed feed, which makes the determination result low. At this time, the operation should be proceed in accordance with 8.4 after weighing the test portion.
Foreword II
1 Scope
2 Normative References
3 Principle
4 Reagents and Materials
5 Apparatus
6 Sampling
7 Preparation of Test Sample
8 Analytical Procedure
9 Calculation of Results
10 Precision
11 Test Report
Annex A (Informative) Structural Changes of This Standard with Respect to ISO 6869:
Annex B (Informative) Technical Deviations between This Standard and the International Standard ISO 6869:2000 and Their Justifications
Annex C (Informative) Results of Interlaboratory Tests
Bibliography
