ISO-5518-2007.pdf
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1、INTERNATIONAL STANDARD ISO 5518 Second edition 2007-02-01 Reference number ISO 5518:2007(E) ISO 2007 Fruits, vegetables and derived products Determination of benzoic acid content Spectrophotometric method Fruits, lgumes et produits drivs Dtermination de la teneur en acide benzoque Mthode spectrophot
2、omtrique Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Defense Supply Ctr/9960866100 Not for Resale, 04/24/2007 11:01:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 5518:2007(E) ii ISO 2007 All rights reserv
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7、country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Defe
8、nse Supply Ctr/9960866100 Not for Resale, 04/24/2007 11:01:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 5518:2007(E) ISO 2007 All rights reserved iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards
9、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 which a technical committee has been established has the right to be represented on that committee. International organizat
10、ions, 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 matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in th
11、e ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards 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
12、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 shall not be held responsible for identifying any or all such patent rights. ISO 5518 was prepared by Technical Committee ISO/TC 34, Food produc
13、ts, Subcommittee SC 3, Fruit and vegetable products. This second edition cancels and replaces the first edition (ISO 5518:1978), which has been technically revised. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Defense Supply Ctr/9960866100
14、Not for Resale, 04/24/2007 11:01:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 5518:2007(E) iv ISO 2007 All rights reserved Introduction A method for determining the benzoic acid content of fruits, vegetable and derivatives, described in 1959, was based on the tech
15、nique of peak emergence. The advantage of this method was that it was specifically intended for benzoic acid, with one exception: p-chlorobenzoic acid. However, it was necessary to make a modification, consisting of purifying the ethereal extract by chromic acid oxidation. This results in the elimin
16、ation of the effects of colouring substances in certain vegetable products containing anthocyanins, and also all the oxybenzoic acids and sorbic acid which may be present if several antiseptics have been used. Moreover, purification increases the sensitivity of the method. This improved technique wa
17、s also more rapid. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Defense Supply Ctr/9960866100 Not for Resale, 04/24/2007 11:01:44 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARDISO 5518:2007(
18、E) ISO 2007 All rights reserved 1 Fruits, vegetables and derived products Determination of benzoic acid content Spectrophotometric method 1Scope This International Standard specifies a method for determining the benzoic acid content of fruits, vegetables and derived products. As chlorobenzoic acids
19、are resistant to oxidation, the method cannot be applied in the presence of p-chlorobenzoic acid, as the absorption spectrum of this acid is close to that of benzoic acid. Neither can it be used in the presence of cinnamic acid, which is transformed into benzoic acid by chromic acid oxidation. NOTET
20、he cinnamic acid determined as benzoic acid in this method exists generally only in the form of traces in vegetables, and therefore has no effect on the result obtained, except in the case of cinnamon bark, which contains higher quantities. 2Principle The test sample is homogenized, followed by dilu
21、tion and acidification of a test portion. The benzoic acid is extracted by diethyl ether, then this acid undergoes alkaline re-extraction and purification by oxidation using acidified potassium dichromate. The purified benzoic acid dissolved in diethyl ether is determined by spectrophotometry. 3Reag
22、ents Use only reagents of recognized analytical quality and distilled water or water of at least equivalent purity. 3.1Tartaric acid COOH(CHOH)2COOH, crystalline. 3.2Sodium hydroxide (NaOH), approximately solution. 3.3Potassium dichromate (K2Cr2O7), solution containing to . 3.4Dilute sulfuric acid (
23、H2SO4), obtained by diluting 2 volumes of concentrated sulfuric acid () with 1 volume of water. 3.5Diethyl ether (CH3CH2)2O, recently distilled. 3.6Benzoic acid (C6H5COOH), standard solution in diethyl ether containing . 3.7Sodium hydrogen carbonate (NaHCO3), crystalline. 4Apparatus Usual laboratory
24、 apparatus and, in particular, the following. 4.1Volumetric flasks, of capacities and . 4.2Beakers, of capacities and . 1 mol/l 33 g/l34 g/l 20=1,84 g/ml 0,100 g/l 50 ml1 000 ml 50 ml100 ml Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Defen
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