1、BSI Standards PublicationBS ISO 18321:2015Essential oils Determinationof peroxide valueBS ISO 18321:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 18321:2015.The UK participation in its preparation was entrusted to TechnicalCommittee AW/54, Essential oils
2、.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2015. Published by BSI Standar
3、dsLimited 2015ISBN 978 0 580 80825 8ICS 71.100.60Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 May 2015.Amendments issued since publicationDate Text affectedB
4、S ISO 18321:2015 ISO 2015Essential oils Determination of peroxide valueHuiles essentielles Dtermination de lindice de peroxydeINTERNATIONAL STANDARDISO18321First edition2015-05-15Reference numberISO 18321:2015(E)BS ISO 18321:2015ISO 18321:2015(E)ii ISO 2015 All rights reservedCOPYRIGHT PROTECTED DOC
5、UMENT ISO 2015, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written
6、 permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 18321:2015ISO
7、 18321:2015(E)Foreword iv1 Scope . 12 Normative references 13 Terms and definitions . 14 Principle 15 Reagents 16 Apparatus . 27 Sampling 28 Preparation of test sample . 29 Procedure. 29.1 Test portion 29.2 Determination . 39.3 Automated potentiometric titration . 310 Expression of results 310.1 Cal
8、culation 310.2 Conversion from mmol/l to meq/kg 311 Precision . 411.1 Repeatability . 411.2 Reproducibility . 4Bibliography 5 ISO 2015 All rights reserved iiiContents PageBS ISO 18321:2015ISO 18321:2015(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of n
9、ational 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 which a technical committee has been established has the right to be represented on that committee. Inter
10、national 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 matters of electrotechnical standardization.The procedures used to develop this document and those inte
11、nded for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www
12、.iso.org/directives).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. Details of any patent rights identified during the development of the document w
13、ill be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expres
14、sions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT), see the following URL: Foreword Supplementary information .The committee responsible for this document is ISO/TC 54, Essential oils.iv ISO 2015 All righ
15、ts reservedBS ISO 18321:2015Essential oils Determination of peroxide value1 ScopeThis International Standard specifies a method for the determination of the peroxide value in an essential oil. The peroxide value is a measure of the oxidation present.2 Normative referencesThe following documents, in
16、whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 212, Essential oils SamplingISO
17、356, Essential oils Preparation of test samplesISO 3696, Water for analytical laboratory use Specification and test methods3 Terms and definitionsFor the purpose of this document, the following terms and definitions apply.3.1peroxide valueIpnumber that expresses, in millimoles (or milliequivalents),
18、 the quantity of peroxide contained in 1 000 ml of the substance4 PrincipleIt is a redox titration of the iodometry type. The iodide ions added to the essential oil oxidize when reacting with peroxides, obtaining iodine which is titrated with thiosulphate. It can be carried out by volumetric or poti
19、entiometric titration.Potientiometric titration is particularly recommended for highly coloured essential oils for which are difficult to appreciate the end point of the coloured indicator (e.g. vetiver essential oil).5 ReagentsDuring the analysis, only reagents of recognized analytical grade and re
20、verse osmosis or distilled or deionized water of Grade 3, as defined in ISO 3696, should be used.5.1 Trichloromethane (chloroform), 99 % (volume/fraction), or cyclohexane, 99,5 % (volume/fraction) for laboratories with restrictions on the use of chloroform.5.2 Glacial acetic acid, 99,5 % (volume/fra
21、ction). Degassed in an ultrasonic bath or by purging with a current pure and dry inert gas (carbon dioxide or nitrogen).5.3 Potassium iodide, saturated solution of potassium iodide in deionised water, freshly prepared. The solution must remain saturated (undissolved crystals must be present). The so
22、lution has to be kept protected from light.INTERNATIONAL STANDARD ISO 18321:2015(E) ISO 2015 All rights reserved 1BS ISO 18321:2015ISO 18321:2015(E)5.4 Sodium thiosulfate solution, 0,01 mol/l (0,01 N) or 0,1 mol/l (0,1 N).5.5 Coloured standard indicator, starch solution 1 % (volume/fraction). It is
23、not necessary for potentiometric titration.6 ApparatusUsual laboratory apparatus and, in particular, the following.6.1 Balance, 1 mg.6.2 Erlenmeyer flask, of capacity 250 ml.6.3 Shaker.6.4 Pipettes, of capacity 1 ml, 10 ml, graduated in 0,1 ml.6.5 Burette, of capacity 10 ml graduated in 0,05 ml.6.6
24、Test tubes, of capacity 50 ml, 100 ml.6.7 Potentiometer.7 SamplingSampling is not included in the method specified in this International Standard. A recommended sampling method is given in ISO 212.It is important that the laboratory receives a representative sample, not damaged or modified during th
25、e transport or storage, before the arrival at the laboratory.8 Preparation of test sampleThe test sample shall be prepared according to ISO 356.The test sample for the determination of peroxide value shall be taken first and the peroxide value shall be determined immediately. Homogenize the sample,
26、preferably without heating and without aireation. Avoid direct solar radiation. Heat solid samples carefully to 10 C above their melting point. Samples with visible impurities shall be filtered.For some products, the amount of extracted essential oil can be lower than 5 g, or the peroxide value of t
27、he essential oil can be over 30 meq of active oxygen per kilogram. In these cases, the user should choose a smaller sample mass.9 Procedure9.1 Test portionIntroduce in an Erlenmeyer flask 10 ml of essential oil to be titrated (see 6.1, 6.3).2 ISO 2015 All rights reservedBS ISO 18321:2015ISO 18321:20
28、15(E)9.2 DeterminationAdd with a test tube (see 6.6) 20 ml of trichloromethane or cyclohexane, 30 ml of glacial acetic acid and 1 ml of potassium iodide, saturated solution (see 5.1, 5.2, 5.3) and add 2 drops starch solution if volumetric titration is carried out.Shake for approximately 1 min. The d
29、issolution acquires an orangey colour.Add about 100 ml of distilled water.Tritate with sodium thiosulfate solution. Use 0,1 mol/l when the expected peroxide value are over 20 mmol/l. Use 0,01 mol/l sodium thiosulfate solution when the expected peroxide value are less than 20 mmol/l.The end point is
30、obtained when the dissolution becomes white.Carry out a blank titration under the same conditions. No more than 0,5 ml of 0,01 mol/l sodium thiosulfate solution should be consumed for this purpose.9.3 Automated potentiometric titrationMany laboratories often use automated equipment for titration. In
31、 this case, some points have to be taken into consideration. If the system works with autosampler, it is strictly necessary to use amber beaker glasses in order to stop the formation of Iodine while the sample remains in the tray. If the addition of potassium iodide wants to be automated, prepare 70
32、 % (volume/fraction) solution in distilled water instead of saturated solution, fill an opaque bottle, and replace it every week. Therefore, the addition of potassium iodide in 9.2 shall be 10 ml instead of 1 ml.10 Expression of results10.1 CalculationThe peroxide value, Ip, in mmol/l, is given by F
33、ormula (1):Ip=()()VV Ntitrant1050 (1)whereV1is the volume, in millilitres, of titrant sodium thiosulphate, used in the main test;V0is the volume, in millilitres, of titrant sodium thiosulphate, used in the blank test;Ntitrantis the concentration of titrant, sodium thiosulphate, 0,1 N (see 5.4).10.2
34、Conversion from mmol/l to meq/kgThe conversion from mmol/l to meq/kg is calculated by Formula (2):meq/kg = mmol/l 2/density (kg/l) (2) ISO 2015 All rights reserved 3BS ISO 18321:2015ISO 18321:2015(E)11 Precision11.1 RepeatabilityThe absolute difference between two independent single test results, ob
35、tained using this method on the same essential oil tested in the same laboratory by the same operator using the same equipment within a short period of time, was not, in more than 5 % in absolute values or 0,1 in relative values11.2 ReproducibilityThe absolute difference between two single test resu
36、lts, obtained using the same method on the same essential oil tested in different laboratories with different operators using different equipment, was not, in more than 10 % in absolute values or 0,3 in relative values.4 ISO 2015 All rights reservedBS ISO 18321:2015ISO 18321:2015(E)Bibliography1 ISO
37、 385-11), Laboratory glassware Burettes Part 1: General requirements1) This standard has been replaced by ISO 385. ISO 2015 All rights reserved 5BS ISO 18321:2015ISO 18321:2015(E) ISO 2015 All rights reservedICS 71.100.60Price based on 5 pagesThis page deliberately left blankBSI is the national body
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