1、Reference number ISO 7485:2000(E) ISO 2000 INTERNATIONAL STANDARD ISO 7485 First edition 2000-08-15 Animal feeding stuffs Determination of potassium and sodium contents Methods using flame-emission spectrometry Aliments des animaux Dtermination des teneurs en potassium et sodium Mthodes par spectrom
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7、 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for whic
8、h a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all ma
9、tters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Stand
10、ard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Internation
11、al Standard ISO 7485 was prepared by Technical Committee ISO/TC 34, Agricultural food products, Subcommittee SC 10, Animal feeding stuffs. Annex A of this International Standard is for information only.INTERNATIONAL STANDARD ISO 7485:2000(E) ISO 2000 All rights reserved 1 Animal feeding stuffs Deter
12、mination of potassium and sodium contents Methods using flame-emission spectrometry 1 Scope This International Standard specifies a calibration method and a standard addition method for the determination of potassium and sodium contents of animal feeding stuffs by flame-emission spectrometry. The st
13、andard addition method applies if it is not known whether the emissions measured for potassium or sodium are subject to matrix effects. The limit of determination for potassium and sodium is 0,04 g/kg. The calibration method applies if such matrix effects have been shown to be absent. 2 Normative re
14、ference The following normative document contains provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on t
15、his International Standard are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently val
16、id International Standards. ISO 6498:1998, Animal feeding stuffs Preparation of test samples. 3P r i n c i p l e The test portion is incinerated to destroy any organic matter. The potassium and sodium are dissolved by treatment with hydrochloric acid. The potassium and sodium contents are determined
17、 by flame-emission spectrometry at wavelengths of 766 nm and 589 nm respectively, by means of a calibration curve (calibration method) or a standard addition graph (standard addition method). 4 Reagents Use only reagents of recognized analytical quality. 4.1 Water, double distilled, or double deioni
18、zed. 4.2 Potassium chloride (KCl), dried for 2 h at (110 2) C. 4.3 Sodium chloride (NaCl), dried for 2 h at (110 2) C. 4.4 Concentrated hydrochloric acid, c(HCl) = 12 mol/l ( 20 (HCl) = 1,19 g/ml). 4.5 Hydrochloric acid, c(HCl) = 6 mol/l. 4.6 Dilute hydrochloric acid, c(HCl) = 0,1 mol/l.ISO 7485:200
19、0(E) 2 ISO 2000 All rights reserved 4.7 Ionization and release buffer solution. Dissolve 50 g of caesium chloride and 250 g of aluminium nitrate nonahydrate Al(NO 3 ) 3 9H 2 O in water. Dilute to 1 litre with water and mix. Store in a plastic bottle, e.g. polyethene or polypropylene. 4.8 Potassium s
20、tandard solutions. 4.8.1 Potassium stock solution, (K) = 1 mg/ml. Weigh 1,906 g of potassium chloride (4.2) and transfer to a 1 000 ml volumetric flask with approximately 250 ml of dilute hydrochloric acid (4.6). Dissolve and dilute to the mark with the hydrochloric acid (4.6). Store in a plastic bo
21、ttle, e.g. polyethene or polypropylene. At room temperature the solution is stable for up to 6 months. 4.8.2 Potassium intermediate solution, (K) = 100 g/ml. Transfer 10 ml of the potassium stock solution (4.8.1) to a 100 ml volumetric flask. Dilute to the mark with dilute hydrochloric acid (4.6) an
22、d mix. Store in a plastic bottle, e.g. polyethene or polypropylene. At room temperature the solution is stable for 1 month. 4.8.3 Potassium calibration solution, (K) = 10 g/ml. Transfer 10 ml of the potassium intermediate solution (4.8.2) to a 100 ml volumetric flask. Add 10 ml of the ionization and
23、 release buffer solution (4.7). Dilute to the mark with dilute hydrochloric acid (4.6) and mix. Prepare fresh on the day of use. 4.9 Sodium standard solutions. 4.9.1 Sodium stock solution, (Na) = 1 mg/ml. Weigh 2,542 g of sodium chloride (4.3) and transfer to a 1 000 ml volumetric flask with approxi
24、mately 250 ml of dilute hydrochloric acid (4.6). Dissolve and dilute to the mark with the hydrochloric acid (4.6). Mix well. Store in a plastics bottle. At room temperature the solution is stable for up to 6 months. 4.9.2 Sodium intermediate solution, (Na) = 100 g/ml. Transfer 10 ml of the sodium st
25、ock solution (4.9.1) to a 100 ml volumetric flask. Dilute to the mark with dilute hydrochloric acid (4.6) and mix. Store in a plastics bottle. At room temperature the solution is stable for 1 month. 4.9.3 Sodium calibration solution, (Na) = 10 g/ml. Transfer 10 ml of the sodium intermediate solution
26、 (4.9.2) to a 100 ml volumetric flask. Add 10 ml of the ionization and release buffer solution (4.7). Dilute to the mark with the hydrochloric acid (4.6) and mix. Prepare fresh on the day of use. 4.10 Biological Certified Reference Materials. For example: V8-Rye flour or V10-Hay (powdered), from the
27、 International Atomic Energy Agency (IAEA), Austria; SRM 157-Wheat flour, SRM 1568a-Rice flour or SRM 1548-Total diet, from the National Institute of Standards and Technology (NIST), USA.ISO 7485:2000(E) ISO 2000 All rights reserved 3 5 Apparatus Usual laboratory equipment and, in particular, the fo
28、llowing. 5.1 Analytical balance, capable of weighing to the nearest 1 mg. 5.2 Muffle furnace, electrically heated, capable of being maintained at (550 20) C. 5.3 Ashing dishes, of platinum or silica. 5.4 Flame photometer with an air-butane, air-propane or air-acetylene flame in a ratio allowing comp
29、lete combustion; or an atomic absorption spectrometer operating in emission mode and equipped to determine potassium and sodium with an air-acetylene flame. 5.5 Sand bath or hot plate, capable of being maintained at approximately 150 C. 5.6 TD (to deliver) precision pipettes or microburette of 5 ml
30、capacity. 5.7 TC (to contain) precision pipettes, of various capacities. 5.8 Beakers, of 250 ml capacity. 5.9 Volumetric flasks, of various capacities. 6 Sampling Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 6497 1. It is
31、important that the laboratory receive a sample which is truly representative and has not been damaged or changed during transport or storage. 7 Preparation of test sample Prepare the test sample in accordance with ISO 6498. 8 Procedure 8.1 Test portion 8.1.1 Samples containing organic matter Dependi
32、ng on the expected content, weigh 1 g to 5 g of the prepared test sample (clause 7) to the nearest 1 mg into an ashing dish (5.3). Proceed in accordance with 8.2.1. 8.1.2 Samples not containing organic matter Depending on the expected content of potassium and sodium, weigh 1 g to 5 g of the prepared
33、 test sample to the nearest 1 mg into a beaker (5.8). Proceed in accordance with 8.2.2.ISO 7485:2000(E) 4 ISO 2000 All rights reserved 8.2 Preparation of test solution 8.2.1 Incineration and rendering silica insoluble Place the incineration dish containing the test portion (8.1.1) in the cold muffle
34、 furnace (5.2). Close the furnace and gradually increase the temperature to 550 C and ash for 3 h at this temperature. If many carbon particles are present, allow to cool down, moisten the contents of the dish with 2 ml of water and dry the dish on the sand bath or hot plate (5.5). Ash for another 2
35、 h at 550 C in the muffle furnace. Allow to cool down, moisten the ash with a few drops of water and transfer it to a 250 ml beaker (5.8). Rinse the incineration dish with a total of approximately 5 ml of concentrated hydrochloric acid (4.4) and then with a few millilitres of water, collecting the r
36、insings in the beaker. CAUTION Take care during the addition of hydrochloric acid, as an effervescent reaction may occur with some samples. Put a watch glass on the beaker to reduce spattering and slowly evaporate the contents of the beaker to near dryness on the sand bath or hot plate (5.5). Allow
37、to cool to room temperature. Proceed in accordance with 8.2.3. 8.2.2 Dissolution of potassium and sodium Add to the beaker containing the test portion (8.1.2), slowly and carefully, a sufficient quantity (15 ml to 30 ml) of concentrated hydrochloric acid (4.4). Put a watch glass on the beaker to red
38、uce spattering and slowly evaporate the contents of the beaker to dryness on the sand bath or hot plate (5.5). Allow to cool to room temperature. 8.2.3 Re-dissolution of potassium and sodium Treat the residue (8.2.1 or 8.2.2) with 5 ml of hydrochloric acid (4.5) and 45 ml of water. Bring to the boil
39、 and allow to cool to room temperature. Transfer quantitatively into a 100 ml volumetric flask. Dilute to the mark with water and mix. Allow particles to settle for at least 4 h. Filter if the solution is not clear. CAUTION Perform the above operations in an effective fume-removal device. 8.3 Blank
40、test solution Prepare a solution in the same way as for the test solution, carrying out all the operations specified in 8.2 but omitting the test portion. 8.4 Selection of method If it is not known whether the emissions measured for potassium or sodium are subject to matrix effects, proceed in accor
41、dance with 8.6. If such matrix effects have been shown to be absent, proceed in accordance with 8.5. 8.5 Calibration method 8.5.1 Test solutions Transfer to a 100 ml volumetric flask an aliquot portion of the test solution (8.2.3) containing a maximum of 1 mg of potassium or sodium. Add 10 ml of the
42、 ionization and release buffer solution (4.7), dilute to the mark with water and mix. Prepare the same dilution of the blank test solution (8.3) in the same way.ISO 7485:2000(E) ISO 2000 All rights reserved 5 8.5.2 Calibration solutions Transfer to six 100 ml volumetric flasks 0 ml, 2,0 ml, 4,0 ml,
43、6,0 ml, 8,0 ml and 10,0 ml of the potassium intermediate solution (4.8.2) or sodium intermediate solution (4.9.2). Add 10 ml of the ionization and release buffer solution (4.7) to each flask. Dilute to the mark with hydrochloric acid (4.6) and mix. The potassium or sodium contents of these solutions
44、 are 0 g/ml, 2,0 g/ml, 4,0 g/ml, 6,0 g/ml, 8,0 g/ml and 10,0 g/ml respectively. Prepare fresh on the day of use. 8.5.3 Spectrometric measurements 8.5.3.1 Adjustment of the instrument Adjust the instrument in accordance with the manufacturers instructions. Light the flame and allow some minutes for f
45、lame stabilization. Adjust the burner position, the gas flows and the wavelengths (theoretically 766 nm for potassium and 589 nm for sodium) or select the filters so that maximum reading is obtained when the calibration solution of potassium (4.8.3) or sodium (4.9.3) is atomized in the flame. 8.5.3.
46、2 Test solution measurements Measure the emissions of the calibration solutions (8.5.2) and then the emission of the test solution (8.5.1). Correct the emission of the test solution for the emission of the diluted blank test solution (8.5.1), if the latter differs from the emission of the zero conce
47、ntration calibration solution. 8.5.4 Calibration graph Draw the calibration graph by plotting the emissions of the calibration solutions against their respective potassium or sodium contents in micrograms per millilitre. 8.6 Standard addition method 8.6.1 Test solutions Carry out the dilutions accor
48、ding to the expected potassium or sodium content. Transfer to each of three volumetric flasks of suitable capacity (flasks A, B and C) the same aliquot portion of the test solution (8.2.3). Add to flasks B and C aliquot portions of the potassium intermediate solution (4.8.2) or sodium intermediate s
49、olution (4.9.2) corresponding to a content of 2,5 g/ml for flask B and 5 g/ml for flask C. Add to each flask an aliquot portion of the ionization and release buffer solution (4.7) corresponding to 10 ml per 100 ml of the final solution. Dilute the contents of the three flasks (A, B and C) to the mark with water and mix. The potassium or sodium content of the solution in flask A shall be smaller than 5 g/ml. Prepare the same dilution of the blank test solution (8.3) in the same way as for
