BS ISO 9874-2006 Milk - Determination of total phosphorus content - Method using molecular absorption spectrometry《牛乳 总磷含量的测定 用分子吸收光谱法》.pdf

1、BRITISH STANDARD BS ISO 9874:2006 Milk Determination of total phosphorus content Method using molecular absorption spectrometryICS 67.100.10 BS ISO 9874:2006 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 22 February 2006 BSI 22 February 200

2、6 ISBN 0 580 47840 8 National foreword This British Standard reproduces verbatim ISO 9874:2006 and implements it as the UK national standard. It supersedes BS 1741-12:1992 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee AW/5, Chemical analysis of milk

3、 and milk products, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue und

4、er the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct app

5、lication. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed; moni

6、tor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii and iii, a blank page, pages 1 to 7 and a back cover. The BSI copyright notice displayed in this document ind

7、icates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsReference numbers ISO 9874:2006(E) IDF 42:2006(E) INTERNATIONAL STANDARD ISO 9874 IDF 42 Second edition 2006-02-01 Milk Determination of total phosphorus content Method using molecular absorption spec

8、trometry BS ISO 9874:2006iiiii 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 intere

9、sted in a subject for which 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

10、Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the tec

11、hnical committees are circulated to the member bodies for voting. Publication as an International Standard 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 document may be the subject of patent rights. ISO

12、 shall not be held responsible for identifying any or all such patent rights. ISO 9874 IDF 42 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF). It is being published jointly by ISO and IDF. This edit

13、ion of ISO 9874 IDF 42 cancels and replaces ISO 9874:1992, of which it constitutes a minor revision. BS ISO 9874:2006blank1 Milk Determination of total phosphorus content Method using molecular absorption spectrometry 1 Scope This International Standard specifies a molecular absorption spectrometric

14、 method for the determination of the total phosphorus content of milk. 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

15、document (including any amendments) applies. ISO 648:1977, Laboratory glassware One-mark pipettes ISO 1042:1998, Laboratory glassware One-mark volumetric flasks ISO 4788:2005, Laboratory glassware Graduated measuring cylinders 3 Terms and definitions For the purposes of this document, the following

16、terms and definitions apply. 3.1 total phosphorus content mass fraction of substances determined by the method specified in this International Standard NOTE It is expressed as a mass fraction in percent. 4 Principle A sample of milk is treated by a wet digestion method using sulfuric acid and hydrog

17、en peroxide, or by dry ashing. Molybdenum blue is formed by the addition of molybdate/ascorbic acid solution. The absorbance at a wavelength of 820 nm is measured spectrophotometrically. 5 Reagents All reagents shall be of recognized analytical grade, unless otherwise specified. The water used shall

18、 be distilled or deionized water, free from phosphorus compounds. 5.1 Concentrated sulfuric acid, 20= 1,84 g/ml, c(H 2 SO 4 ) 18 mol/l. 5.2 Dilute sulfuric acid,c(H 2 SO 4 ) 5 mol/l. Carefully add, while stirring continuously, 278 ml of concentrated sulfuric acid (5.1) to 722 ml of water. BS ISO 987

19、4:20062 5.3 Dilute hydrochloric acid,c(HCI) 1 mol/l. (Used for dry ashing.) Dilute 83 ml of concentrated hydrochloric acid ( 20= 1,19 g/ml) to 1 000 ml with water. 5.4 Hydrogen peroxide,c(H 2 O 2 ) 9 mol/l, free from phosphorus-containing substances. 5.5 Sodium molybdate solution,c(Na 2 MoO 4 ) 0,1

20、mol/l. Weigh 2,5 g of sodium molybdate dihydrate into a 100 ml one-mark volumetric flask (6.10). Add a sufficient volume of dilute sulfuric acid (5.2) to dissolve the sodium molybdate dihydrate. Dilute to the mark with the same sulfuric acid (5.2) and mix. 5.6 Ascorbic acid solution,c(C 6 H 8 O 6 )

21、0,25 mol/l. Weigh 5 g of ascorbic acid into a 100 ml one-mark volumetric flask (6.10). Add a sufficient volume of water to dissolve the ascorbic acid. Dilute to the mark with water and mix. This solution shall be freshly prepared. 5.7 Molybdate/ascorbic acid solution. Immediately before use, add 25

22、ml of the sodium molybdate solution (5.5) to 10 ml of the ascorbic acid solution (5.6) in a 100 ml one-mark volumetric flask (6.10). Dilute to the mark with water and mix. 5.8 Standard solution A. Dry about 1 g of potassium dihydrogen orthophosphate (KH 2 PO 4 ) for at least 48 h in a desiccator (6.

23、14). Weigh 0,439 4 g of the dried phosphate into a 1 000 ml one-mark volumetric flask (6.10). Dilute to the mark with water and mix. The phosphorus content of this standard solution is 100 mg/l. 5.9 Standard solution B. Pipette 10 ml of the standard solution A (5.8) into a 100 ml one-mark volumetric

24、 flask (6.10). Dilute to the mark with water and mix well. The phosphorus content of this standard solution is 10 mg/l. 6 Apparatus IMPORTANT All glassware shall be thoroughly cleaned using a phosphorus-free detergent and then rinsed with water. Usual laboratory equipment and, in particular, the fol

25、lowing. 6.1 Analytical balance, accurate to the nearest 0,1 mg. 6.2 Water bath, capable of operating at 100 C. 6.3 Oven, capable of operating at 100 C. 6.4 Electric heater or micro gas burner. 6.5 Digestion flask (Kjeldahl) or test tubes, of 50 ml capacity. 6.6 Glass beads, of approximately 5 mm dia

26、meter. BS ISO 9874:20063 6.7 Dish, made of platinum or silica, of approximately 55 mm diameter, and a suitable watch-glass. 6.8 Electric furnace with air circulation, capable of operating at 500 C to 550 C. 6.9 Graduated cylinders, of 5 ml and 25 ml capacity, in accordance with the requirements of I

27、SO 4788. 6.10 One-mark volumetric flasks, of 50 ml, 100 ml and 1 000 ml capacity, in accordance with the requirements of ISO 1042:1998, class B. 6.11 One-mark pipettes, delivering 1 ml, 2 ml, 3 ml, 5 ml and 10 ml, in accordance with the requirements of ISO 648:1997, class B. 6.12 Molecular absorptio

28、n spectrometer, suitable for measurements at a wavelength of 820 nm, equipped with cells of 10 mm optical path length. 6.13 Filter paper, medium grade. 6.14 Desiccator, containing an efficient drying agent. 7 Sampling A representative sample should have been sent to the laboratory. It should not hav

29、e been damaged or changed during transport or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 707 IDF 50 1 . 8 Preparation of test sample Bring the laboratory sample to 20 C 2 C and mix carefully. If a homogeneous di

30、spersion of the fat is not obtained, heat the sample slowly to 40 C, mix gently and cool to 20 C 2 C, before taking a test sample for analysis. 9 Procedure 9.1 Wet-digestion method 9.1.1 Weigh into a digestion flask (6.5), to the nearest 1 mg, a test portion of about 1,5 g of the test sample (Clause

31、 8). Add three glass beads (6.6) and 4 ml of the concentrated sulfuric acid (5.1). 9.1.2 Operating under a well-ventilated fume hood provided with a water scrubbing system, place the flask in an inclined position and heat using the electric heater or micro gas burner (6.4). Control the heating so as

32、 to limit the production of foam in the flask. Keep the mixture boiling gently. Avoid local overheating and avoid heating the flask above the surface of the liquid contents. 9.1.3 As soon as the foaming stops, cool the mixture in air to room temperature. Carefully add 2 ml of the hydrogen peroxide (

33、5.4) and reheat. Repeat this procedure until the contents have become clear and colourless. During heating, mix the contents from time to time by swirling carefully. Avoid local overheating. 9.1.4 Cool the mixture in air to room temperature and rinse the neck of the flask with about 2 ml of water. H

34、eat the contents again until the water has evaporated. Allow the liquid to boil for 30 min in order to destroy all traces of hydrogen peroxide. Avoid local overheating. BS ISO 9874:20064 9.1.5 Cool the mixture in air to room temperature. Quantitatively transfer the liquid contents into a 100 ml one-

35、mark volumetric flask (6.10). Dilute to the mark with water and mix well. 9.1.6 Pipette 2 ml of the test solution into a 50 ml one-mark volumetric flask (6.10) and dilute with about 25 ml of water. Add 2,0 ml of the molybdate/ascorbic acid solution (5.7). Dilute to the mark with water and mix well.

36、9.1.7 Boil the contents of the flask in the water bath (6.2) for 15 min. 9.1.8 Cool the mixture to room temperature in cold water. Proceed as specified in 9.5. The spectrometric determination should be carried out within 1 h. 9.2 Dry-ashing method 9.2.1 Weigh, to the nearest 1 mg, a test portion of

37、about 10 g of the test sample (Clause 8) into a platinum or silica dish (6.7). 9.2.2 Evaporate to dryness in an oven (6.3) set at 100 C or lower, or on the water bath (6.2). 9.2.3 After drying is complete, heat the test sample in the electric furnace (6.8) at a temperature between 500 C and 550 C un

38、til white (or nearly white) ash is obtained. The dish should preferably be heated on a hotplate to burn off ignitable contents before being placed in the furnace. 9.2.4 Allow the dish and contents to cool in the furnace and then cover with a watch-glass. Dissolve the ash in 2 ml or 3 ml of the dilut

39、e hydrochloric acid (5.3) and dilute with about 3 ml of water. 9.2.5 Quantitatively transfer the solution of ash to a 100 ml one-mark volumetric flask (6.10). Rinse the watch-glass and dish with water and transfer the washings to the flask. Dilute to the mark with water and mix well. Filter through

40、a medium-grade filter paper (6.13). 9.2.6 Pipette 10 ml of the filtrate into a 100 ml one-mark volumetric flask (6.10). Dilute to the mark with water and mix well. 9.2.7 Pipette 2 ml of the test solution into a 50 ml one-mark volumetric flask (6.10) and dilute with about 25 ml of water. Add 2,0 ml o

41、f the molybdate/ascorbic acid solution (5.7). Dilute to the mark with water and mix well. 9.2.8 Boil the contents of the flask in the water bath (6.2) for 15 min. 9.2.9 Cool the mixture to room temperature in cold water. Proceed as specified in 9.5. The spectrometric determination should be carried

42、out within 1 h. 9.3 Blank test Carry out a blank test concurrently with the determination, using the same procedure as for the test portion (9.1 or 9.2) but using 1,5 ml or 10 ml, respectively, of phosphorus-free water in place of the test portion. 9.4 Calibration graph 9.4.1 Pipette, into a series

43、of five 50 ml one-mark volumetric flasks (6.10), 0 ml, 1 ml, 2 ml, 3 ml and 5 ml, respectively, of the standard solution B (5.9). Dilute the contents of each flask to approximately 25 ml with water. BS ISO 9874:20065 9.4.2 Add to the contents of each volumetric flask, 2,0 ml of the molybdate/ascorbi

44、c acid solution (5.7). Dilute each solution to the mark with water and mix well. The resulting solutions contain 0 g, 10 g, 20 g, 30 g, and 50 g of phosphorus, respectively, per 50 ml. 9.4.3 Boil the contents of the flasks in the water bath (6.2) for 15 min. 9.4.4 Cool the solutions to room temperat

45、ure in cold water. Within 1 h, measure the absorbance of each of the calibration solutions against that of the solution containing 0 g of phosphorus (see 9.4.2) using the spectrometer (6.12) at a wavelength of 820 nm, with cells of 10 mm optical path length. If the absorbance value of the solution c

46、ontaining 0 g of phosphorus per 50 ml is high, check the reagents. 9.4.5 Plot the net absorbance values obtained against the mass, in micrograms, of phosphorus contained in the calibration solutions (9.4.2). 9.5 Spectrometric measurement Within 1 h, carry out the spectrometric measurements on the te

47、st solution (9.1.8 or 9.2.9) against the blank (9.3) using the spectrometer (6.12) at a wavelength of 820 nm with cells of 10 mm optical path length. 10 Expression of results Using the calibration graph (9.4), determine the mass of phosphorus corresponding to the net absorbance value of the test sol

48、ution. Calculate the total phosphorus content w P , expressed as a mass fraction in percent, using the following formula. a) Wet-digestion method 1 P 0 200 m w m b) Dry-ashing method 1 P 0 20 m w m where m 0is the mass of the test portion (9.1.1 or 9.2.1), in grams; m 1is the mass of phosphorus, rea

49、d or calculated from the calibration graph, in micrograms. Report the result to the third decimal place. 11 Precision 11.1 Interlaboratory test The precision of the method has been established by an international interlaboratory test (see Reference 2 in the Bibliography) carried out in accordance with ISO 5725 3 . The values obtained for repeatability and reproducibility are expressed at the 95 % probability