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1、BRITISH STANDARD BS 1741-12: 1992 ISO 9874:1992 Methods for Chemical analysis of liquid milk and cream Part 12: Determination of total phosphorus content of milk Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1741-12:1992 This British St
2、andard, having been prepared under the direction of the Agriculture and Food Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 June 1992 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference AF
3、C/3 Draft for comment 89/54370 DC ISBN 0 580 20851 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Agriculture and Food Standards Policy Committee (AFC/-) to Technical Committee AFC/3, upon which the following bodies were represented:
4、Association of British Preserved Milk Manufacturers Association of Public Analysts of Scotland Creamery Proprietors Association Department of Trade and Industry (Laboratory of the Government Chemist) Intervention Board for Agricultural Produce Joint Committee of the Milk Marketing Board and the Dair
5、y Trade Federation Milk Marketing Board Milk Marketing Board for Northern Ireland Ministry of Agriculture, Fisheries and Food Royal Association of British Dairy Farmers Royal Society of Chemistry Society of Dairy Technology Amendments issued since publication Amd. No.DateComments Licensed Copy: shef
6、fieldun sheffieldun, na, Fri Nov 24 08:01:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1741-12:1992 BSI 10-1999i Contents Page Committees responsibleInside front cover National forewordii 1Scope1 2Normative references1 3Definition1 4Principle1 5Reagents1 6Apparatus1 7Sampling2 8Preparation of th
7、e test sample2 9Procedure2 10Expression of results3 11Precision3 12Test report4 Annex A (informative) Bibliography5 List of referencesInside back cover Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1741-12:1992 ii BSI 10-1999 National f
8、oreword This Part of BS 1741, which has been prepared under the direction of the Agriculture and Food Standards Policy Committee, is identical with ISO 9874:1992 Milk Determination of total phosphorus content Method using molecular absorption spectrometry, prepared by ISO/TC 34, Agricultural food pr
9、oducts, of the International Organization for Standardization (ISO) in cooperation with the International Dairy Federation (IDF) and the Association of Official Analytical Chemists (AOAC). NOTEThis Part should be read in conjunction with Part 1 General introduction including preparation of samples,
10、published separately. The Technical Committee has reviewed the provisions of ISO 648:1977, to which normative reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. A related British Standard to ISO 648:1977 is BS 1583:1986. One-mark pipett
11、es conforming to BS 1583 may be used in place of those conforming to ISO 648:1977. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itsel
12、f confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 707:1985BS 809:1985 Methods for sampling of milk and milk products (Identical) ISO 1042:1983BS 1792:1982 Specification for one-mark volumetric flasks (Identical) ISO 4788:1980BS 604:1
13、982 Specification for graduated glass measuring cylinders (Identical) ISO 5725:1986BS 5497 Precision of test methods Part 1:1987 Guide for the determination of repeatability and reproducibility for a standard test method by inter- laboratory tests (Identical) Summary of pages This document comprises
14、 a front cover, an inside front cover, pages i and ii, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldu
15、n sheffieldun, na, Fri Nov 24 08:01:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1741-12:1992 BSI 10-19991 1 Scope This International Standard specifies a spectrometric method for the determination of the total phosphorus content of milk. 2 Normative references The following standards contain pr
16、ovisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the
17、 possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 648:1977, Laboratory glassware One-mark pipettes. ISO 1042:1983, Laboratory glassware One-mark volumetric flasks. ISO 4788:198
18、0, Laboratory glassware Graduated measuring cylinders. 3 Definition For the purposes of this International Standard, the following definition applies. 3.1 total phosphorus content: the mass fraction of substances determined by the method specified in this International Standard. It is expressed as a
19、 percentage (m/m) 4 Principle Wet digestion of milk using sulfuric acid and hydrogen peroxide, or dry ashing of milk. Formation of molybdenum blue by the addition of molybdate/ascorbic acid solution. Spectrometric measurement of the absorbance at a wavelength of 820 nm. 5 Reagents All reagents shall
20、 be of recognized analytical grade, unless otherwise specified. The water used shall be distilled or deionized water, free from phosphorus compounds. 5.1 Concentrated sulfuric acid, 20 = 1,84 g/ml c(H2SO4) = 18 mol/l approximately. 5.2 Dilute sulfuric acid, c(H2SO4) = 5 mol/l approximately. Carefull
21、y add, while stirring continuously, 278 ml of concentrated sulfuric acid (5.1) to 722 ml of water. 5.3 Hydrochloric acid, c(HCl) = 1 mol/l approximately. (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(H2O2) = 9 m
22、ol/l approximately, free from phosphorus-containing substances. 5.5 Sodium molybdate, c(Na2MoO4) = 0,1 mol/l approximately. 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 solution (5.2) to dissolve the sodium
23、molybdate dihydrate. Make up to the mark with the same acid (5.2) and mix. 5.6 Ascorbic acid, c(C6H8O6) = 0,25 mol/l approximately. 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. Make up to the mark with wate
24、r and mix. This solution shall be freshly prepared. 5.7 Molybdate/ascorbic acid solution. Immediately before use, add 25 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). Make up to the mark with water and mix. 5.8 St
25、andard solution A. Dry about 1 g of potassium dihydrogen orthophosphate (KH2PO4) for at least 48 h in a desiccator (6.14). Weigh 0,439 4 g of the dried phosphate into a 1 000 ml one-mark volumetric flask (6.10). Make up to the mark with water and mix. The phosphorus content of this standard solution
26、 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 flask (6.10). Make up 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 clea
27、ned using a phosphorus-free detergent and then rinsed with water. Usual laboratory equipment and, in particular, the following. 6.1 Analytical balance, accurate to the nearest 1 mg. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1741-12:
28、1992 2 BSI 10-1999 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 flasks (Kjeldahl) or test tubes, of 50 ml capacity. 6.6 Glass beads, of approximately 5 mm diameter. 6.7 Dish, made of platinum or silica,
29、 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, complying with the requirements of ISO 4788. 6.10 One-mark volumetric flasks, of 50 ml, 100 ml and 1 0
30、00 ml capacity, complying with the requirements of ISO 1042, class B. 6.11 One-mark pipettes, delivering 1 ml, 2 ml, 3 ml, 5 ml and 10 ml, complying with the requirements of ISO 648, class B. 6.12 Molecular absorption spectrometer, suitable for measurements at a wavelength of 820 nm, equipped with c
31、ells of 10 mm optical path length. 6.13 Filter paper, medium grade. 6.14 Desiccator, containing an efficient drying agent. 7 Sampling Sampling should have been carried out in accordance with ISO 707 1. Store the laboratory sample in such a way that deterioration and change in its composition are pre
32、vented. 8 Preparation of the test sample Bring the laboratory sample to 20 C 2 C and mix carefully. If a homogeneous dispersion 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
33、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 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 th
34、e flask in an inclined position and heat using the electric heater or micro gas burner (6.4). Control the heating so as to limit the production of foam in the flask. Keep the mixture gently boiling. Avoid local overheating and heating the flask above the surface of the liquid contents. 9.1.3 As soon
35、 as the foaming stops, cool the mixture in air to room temperature. Carefully add 2 ml of the hydrogen peroxide solution (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
36、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. Heat 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. 9.1.5 Coo
37、l the mixture in air to room temperature. Quantitatively transfer the liquid contents into a 100 ml one-mark volumetric flask (6.10). Make up 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 wate
38、r. Add 2,0 ml of the molybdate/ascorbic acid solution (5.7). Make up to the mark with water and mix well. 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. NOTE 1The spectrometric determinat
39、ion 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 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 dr
40、ying is complete, heat the test sample in the electric furnace (6.8) at a temperature between 500 C and 550 C until white (or nearly white) ash is obtained. NOTE 2The dish should preferably be heated on a hotplate to burn off ignitable contents before being placed in the furnace. 9.2.4 Allow the dis
41、h 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 hydrochloric acid solution (5.3) and dilute with about 3 ml of water. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1741-12
42、:1992 BSI 10-19993 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. Make up to the mark with water and mix well. Filter through a medium-grade filter paper (6.13). 9.2.6 P
43、ipette 10 ml of the filtrate into a 100 ml one-mark volumetric flask (6.10). Make up 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 of the molybdate/ascorbic acid solution (5.
44、7). Make up 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. NOTE 3The spectrometric determination should be carried out within 1 h. 9.3 Blank test Carr
45、y 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 of five 50 ml one-mark volumetric flask
46、s (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. 9.4.2 Add to the contents of each volumetric flask 2,0 ml of the molybdate/ascorbic acid solution (5.7). Make each solution up to the mark wit
47、h water and mix well. The resulting solutions contain 0 4g, 10 4g, 20 4g, 30 4g and 50 4g 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 temperature in cold water. Within 1 h, measure the absorbance o
48、f each of the calibration solutions against that of the solution containing 0 4g of P (see 9.4.2) using the spectrometer (6.12) at a wavelength of 820 nm, with cells of 10 mm optical path length. NOTE 4If the absorbance value of the solution containing 0 4g of P per 50 ml is high, check the reagents
49、. 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 test 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 solution. Calculate th