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1、BRITISH STANDARD BS ISO 7238:2004 Butter Determination of pH of the serum Potentiometric method ICS 67.100.20 ? Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 7238:2004 This British Standard was published under the authority of the S
2、tandards Policy and Strategy Committee on 8 December 2004 BSI 8 December 2004 ISBN 0 580 44987 4 National foreword This British Standard reproduces verbatim ISO 7238:2004 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee AW/5,
3、 Milk 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 Catalogu
4、e under 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 correc
5、t application. 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 the UK interests infor
6、med; monitor 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 to v, a blank page, pages 1 to 5 and a back page. The BSI copyright notice displayed in this documen
7、t indicates when the document was last issued. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Reference numbers ISO 7238:2004(E) IDF 104:2004(E) OSI DI dnaF 4002 INTERNATIONAL STANDA
8、RD ISO 7238 IDF 104 Second edition 2004-12-01 Butter Determination of pH of the serum Potentiometric method Beurre Dtermination du pH de la phase aqueuse Mthode potentiomtrique BS ISO 7238:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI
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14、 +0 337 2 23 431 -Email copyrightisoo.rg -Emailni off-lidif.org We bwww.is.o groWe bwww.fil-idf.o gr Plbuisdehi n Switlrez dna ii ISO dnaID 4002 FA ll rihgtsser edevr BS ISO 7238:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:8327 O
15、4002(E) ID:401 F002(4)E I SO dna ID 4002 F All irhgts seredevr iii Contents Forewordiv 1 Scope1 2 Normative references .1 3 Terms and definitions.1 4 Principle.1 5 Reagents1 6 Apparatus.2 7 Sampling2 8 Procedure.3 8.1 Test portion .3 8.2 Separation of the serum.3 8.3 Calibration of the pH-meter3 8.4
16、 Determination3 8.5 Cleaning the electrodes3 9 Expression of results3 10 Precision4 10.1 Repeatability4 10.2 Reproducibility4 11 Test report4 Bibliography .5 BS ISO 7238:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:8327 O4002(E) I
17、D:401 F002(4)E iv I SO dna ID 4002 F All irhgts seredevr 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 committee
18、s. Each member body interested 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 Inter
19、national Electrotechnical 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 St
20、andards adopted by the technical 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 sub
21、ject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 7238IDF 104 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF), in collaboration with AOAC In
22、ternational. It is being published jointly by ISO and IDF and separately by AOAC International. This edition of ISO 7238IDF 104 cancels and replaces ISO 7238:1983, of which it constitutes a minor revision. Only editorial changes have been made. BS ISO 7238:2004 Licensed Copy: sheffieldun sheffieldun
23、, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:8327 O4002(E) ID:401 F002(4)E I SO dna ID 4002 F All irhgts seredevr v Foreword IDF (the International Dairy Federation) is a worldwide federation of the dairy sector with a National Committee in every member country. Every Nati
24、onal Committee has the right to be represented on the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO and AOAC International in the development of standard methods of analysis and sampling for milk and milk products. Draft International Standards adopted by the Act
25、ion Teams and Standing Committees are circulated to the National Committees for voting. Publication as an International Standard requires approval by at least 50 % of the National Committees casting a vote. ISO 7238IDF 104 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC
26、 5, Milk and milk products, and the International Dairy Federation (IDF), in collaboration with AOAC International. It is being published jointly by ISO and IDF and separately by AOAC International. All work was carried out by the Joint ISO/IDF/AOAC Group of Experts, pH of butter (E36), under the ae
27、gis of its project leader, Mr L.J. Pootvliet (NL). This edition of ISO 7238IDF 104 cancels and replaces IDF 104A:1984. Only editorial changes have been made. BS ISO 7238:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI blank 4002:8327 OS
28、I SB Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI NITERNATNOIAL STANDARD IS:8327 O4002(E) ID:401 F002(4)E I SO dna ID 4002 F All irhgts seredevr 1 Butter Determination of pH of the serum Potentiometric method 1 Scope This International St
29、andard specifies a potentiometric method for the determination of the pH of the serum from all types of butter. 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 referenc
30、es, the latest edition of the referenced document (including any amendments) applies. ISO 3696:1987, Water for analytical laboratory use Specification and test methods 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 pH of butter serum potenti
31、al difference at the measuring temperature between two electrodes immersed in butter serum, determined by the procedure specified in this International Standard NOTE It is expressed in pH units. 4 Principle The potential difference is measured between a glass electrode and a reference electrode in t
32、he serum separated from melted butter. 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and recently distilled water that has been protected from absorption of carbon dioxide and that complies with the requirements for grade 1 water specified in ISO 3696:1987.
33、 BS ISO 7238:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:8327 O4002(E) ID:401 F002(4)E 2 I SO dna ID 4002 F All irhgts seredevr 5.1 Buffer solutions, for calibration of the pH-meter. Two standard buffer solutions, having pH value
34、s known to the second decimal place at the measuring temperature, and which will bracket the pH value of the serum obtained from the test portion, shall be used, for example a buffer solution of pH approximately 4 and another of pH approximately 7. EXAMPLES The following buffer solutions may be used
35、: a) Buffer solution of pH 4,00 at 20 C and 4,01 at 25 C Dissolve, in water, 10,12 g of potassium hydrogen phthalate (KHC8H4O4), which has been previously dried to constant mass at 120 C. Make up to 1 000 ml with water at the measuring temperature and mix well. Preserve the solution by adding approx
36、imately 2 ml of chloroform or carbon tetrachloride. b) Buffer solution of pH 6,88 at 20 C and 6,86 at 25 C Dissolve, in water, 3,388 g of potassium dihydrogen orthophosphate (KH2PO4) and 3,533 g of disodium hydrogen orthophosphate (Na2HPO4), both compounds having been previously dried to constant ma
37、ss at 120 C. Make up to 1 000 ml with water at the measuring temperature and mix well. Preserve the solution by adding approximately 2 ml of chloroform or carbon tetrachloride. 6 Apparatus Usual laboratory apparatus and, in particular, the following. 6.1 pH-meter, of minimum sensitivity 0,01 pH unit
38、, with a glass electrode and a suitable reference electrode, and with temperature compensation. The glass and reference electrodes may be assembled into a system of combined electrodes. 6.2 Centrifuge (if required), of the vertical-loading type1), capable of attaining a relative radial acceleration
39、of approximately 375 g. 6.3 Centrifuge tubes (if required), of capacity approximately 50 ml, with suitable stoppers. 6.4 Test tubes, of capacity approximately 12 ml, internal diameter 16 mm to 20 mm. 6.5 Water bath (if required), capable of being maintained at 65 C. 6.6 Ice-water bath (if required).
40、 6.7 Calibrated thermometer, accurate to 1 C. 7 Sampling A representative sample should have been sent to the laboratory. It should not have been damaged or changed during transport or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling method
41、 is given in ISO 707 1. 1) For details of a suitable centrifuge, reference should be made to ISO 2446:1976, 6.6. BS ISO 7238:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:8327 O4002(E) ID:401 F002(4)E I SO dna ID 4002 F All irhgts
42、seredevr 3 8 Procedure 8.1 Test portion Take approximately 50 g of the sample. 8.2 Separation of the serum Separate the serum from the butter by an appropriate method (see the Note). Transfer the serum (including the protein) to a test tube (6.4), and bring it to the measuring temperature. NOTE Ther
43、e are many methods for the separation of the serum from the butter, one of which is as follows. Transfer the test portion to a centrifuge tube (6.3), and place the centrifuge tube in the water bath (6.5). Two layers will be formed by the melting butter. As soon as the butter has melted (after 3 min
44、to 5 min), close the centrifuge tube with the stopper, place it, with the stoppered end downwards, in the tube holder and centrifuge for 5 min at a relative radial acceleration of approximately 375 g. Immediately immerse the centrifuge tube, with the stoppered end downwards, in the ice-water bath (6
45、.6) and leave until the fat has completely congealed. 8.3 Calibration of the pH-meter Adjust the temperature of the buffer solutions (5.1) to the measuring temperature and calibrate the pH-meter in accordance with the manufacturers instructions. If a series of samples is being tested, check the cali
46、bration of the pH-meter with one or both buffer solutions at least every 30 min. 8.4 Determination Introduce the electrodes into the serum at the measuring temperature. Carry out the determination using the procedure appropriate to the pH-meter used. When the reading becomes constant, read the pH di
47、rectly from the scale of the instrument, to the nearest 0,01 pH unit. Introduce the thermometer (6.7) into the serum and read the measuring temperature. 8.5 Cleaning the electrodes Clean the electrodes by rinsing consecutively with acetone at room temperature and water at 30 C to 35 C. Dab them dry
48、with a clean paper tissue. 9 Expression of results Record the measured pH to the nearest 0,01 pH unit, together with the measuring temperature. BS ISO 7238:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:46:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:8327 O4002(E) ID:401 F002(4)E
49、 4 I SO dna ID 4002 F All irhgts seredevr 10 Precision 10.1 Repeatability The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, will in not more than 5 % of cases be greater than 0,03 pH unit. 10.2 Reproducibility The absolute difference between two single test results, obtained usi