1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 12492:2012Rubber, raw Determination of water content by Karl Fischer methodBS ISO 12492:2012 BRITISH STANDARDNational forewordThis British Standard is the UK implementatio
2、n of ISO 12492:2012. The UK participation in its preparation was entrusted to T e c h n i c a l Committee PRI/23, Test methods for rubber and non-black compounding ingredients.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not
3、purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2012. Published by BSI Standards Limited 2012.ISBN 978 0 580 66143 3 ICS 83.040.10 Compliance with a British Standard cannot confer immunity from legal
4、obligations.This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2012.Amendments issued since publicationDate T e x t a f f e c t e dBS ISO 12492:2012 ISO 2012Rubber, raw Determination of water content by Karl Fischer methodCaoutchouc b
5、rut Dtermination de la teneur en eau par la mthode de Karl FischerINTERNATIONAL STANDARDISO12492First edition2012-10-01Reference numberISO 12492:2012(E)BS ISO 12492:2012ISO 12492:2012(E)ii ISO 2012 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2012All rights reserved. Unless otherwise specifie
6、d, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase po
7、stale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 12492:2012ISO 12492:2012(E) ISO 2012 All rights reserved iiiContents PageForeword ivIntroduction v1 Scope . 12 Normative references 13 Principle 14 Reagents 25 Ap
8、paratus . 26 Calibration 37 Sampling and preparation of test piece 38 Procedure. 38.1 Power on . 38.2 Selection of the generator electrode 48.3 Filling the electrolysis cell . 48.4 Equipment check . 48.5 Analysis 59 Precision . 610 Test report . 6Annex A (normative) Calibration schedule . 7BS ISO 12
9、492:2012ISO 12492:2012(E)ForewordISO (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 interested in
10、 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 Commiss
11、ion (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 technical co
12、mmittees 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 shall not
13、 be held responsible for identifying any or all such patent rights.ISO 12492 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee SC 2, Testing and analysis.iv ISO 2012 All rights reservedBS ISO 12492:2012ISO 12492:2012(E)IntroductionThe water content of raw rubber
14、 is one of the important characteristics to be determined as a quality control test. Different synthetic rubbers contain varying amounts of water. Water can affect product quality, texture, shelf life, chemical stability and reactivity. A high amount of water can cause processing difficulties.Water
15、contamination is a cause for major concern in a large number of applications. In the rubber industry, water is one of the major damaging contaminants and is often overlooked as a primary cause of component failure. For certain applications in the rubber industry, even a small amount of water may hav
16、e damaging effects on production.Several methods are available for the determination of water content. A Karl Fischer (KF) coulometric titrator is one of the most accurate methods. Unlike other techniques, it can trace low levels of free, emulsified and dissolved water (which cannot be detected with
17、 normal gravimetric methods). The test is capable of measuring water levels as low as 0,01 %.Unlike gravimetric measurements, which are indirect methods that assume, all volatiles removed are water, Karl Fischer titration is a direct method that is almost specific for water. The method is especially
18、 useful for low moisture levels (1 %).The new test method will help to determine the water content of the raw rubber and rubber compounds in shortest possible time and will be helpful for quality control at the laboratories. Coulometric determination of water is an absolute method. ISO 2012 All righ
19、ts reserved vBS ISO 12492:2012BS ISO 12492:2012Rubber, raw Determination of water content by Karl Fischer methodWARNING Persons using this International Standard should be familiar with normal laboratory practice. This International Standard does not purport to address all of the safety problems, if
20、 any, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions.CAUTION Certain procedures specified in this International Standard may involve the use or generation of substance
21、s, or the generation of waste, that could constitute a local environmental hazard. Reference should be made to appropriate documentation on safe handling and disposal after use.1 ScopeThis International Standard specifies a test method for the determination of water content of raw rubber and compoun
22、ded rubber using a coulometric Karl Fischer titration method. It applies to the water content range between 0,01 % and 1 %. As this is a very sensitive method, contact of sample with any moisture, even from the surrounding environment, must be eliminated as much as possible.2 Normative referencesThe
23、 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 document (including any amendments) applies.ISO 760, Determination of water Karl Fischer method (
24、General method)ISO 1795, Rubber, raw natural and raw synthetic Sampling and further preparative procedure ISO 18899:2004, Rubber Guide to the calibration of test equipment3 PrincipleThe water determination test (Karl Fischer method) is designed to determine the water content in substances, utilizing
25、 the quantitative reaction of water with iodine and sulfur dioxide in the presence of a lower alcohol such as methanol and an organic base, as shown in the following formulae:H2O + I2+ SO2+ 3 RN 2(RN+H)I-+ RNSO3RNSO3+ CH3OH (RN+H)O-SO2OCH3. There are two determination methods which differ in the way
26、 the iodine is provided: the volumetric titration method and the coulometric titration method.In the volumetric titration method, iodine required for reaction with water is previously dissolved and the water content is determined by measuring the amount of iodine consumed as a result of reaction wit
27、h water present in a sample.In the coulometric titration method, first, iodine is produced by electrolysis of the reagent containing iodide ion, then the water content in a sample is determined by measuring the quantity of electricity which is required for the electrolysis, i.e. for the production o
28、f iodine, based on the quantitative reaction of the generated iodine with water.INTERNATIONAL STANDARD ISO 12492:2012(E) ISO 2012 All rights reserved 1BS ISO 12492:2012ISO 12492:2012(E)In coulometric Karl Fischer titration, iodine (I2) is generated electrochemically from iodide (I). When iodine (I2)
29、 comes in contact with the water in the sample, water is titrated according to the above mentioned reaction scheme. Once all of the water available has reacted, the reaction is complete. The amount of water in the sample is calculated by measuring the current needed for the electrochemical generatio
30、n of iodine (I2) from iodide (I) according to the following reaction:222IIe+ According to Faradays Law, the quantity of the iodine produced is proportional to the current generated. In the above equation, I2and H2O react with each other in proportion of 1:1. Therefore, a mole of water (18 g) is equi
31、valent to 2 96 500 coulombs, or 10,72 coulombs/1 mg of H2O.Conveying the water contained within the sample to the titration cell is an important part of the titration. The volumetric flow rate of the carrier (nitrogen) gas is precisely controlled by the flow controller. The sample remains in the sam
32、ple boat. The carrier gas is dried by passing it through silica gel and zeolite type desiccants. The dry carrier gas enters the sample heating chamber and carries the total moisture into the titration cell. The carrier gas passes through the titration cell as long for as the sample is being heated.
33、In this process, the major quantity of water is released at the beginning. The set-up and the connection of the oven are illustrated by the figure below:Thus, the total amount of moisture can be determined by measuring the total consumption of electricity.4 Reagents4.1 Water standard for coulometric
34、 Karl Fischer titration, 0,1 % (NIST Traceable).4.2 Anode solution (for use when a titration cell with a diaphragm is being used).4.3 Cathode solution (for use when a titration cell with a diaphragm is being used).4.4 Universal reagent (for use when a titration cell without a diaphragm is being used
35、).4.5 Dry N2gas of instrument grade.4.6 Aluminium oxide.4.7 Ethanol.4.8 Concentrated HNO3.4.9 Hexane.5 Apparatus5.1 Coulometric Karl Fischer titrator with evaporator. Different components of coulometric Karl Fischer titrator are shown in Figure 1.The water evaporator consists of an oven capable of h
36、eating the test portion to 300 C, a heating tube, a temperature control unit, a carrier-gas flow meter and carrier-gas drying tubes containing desiccant.2 ISO 2012 All rights reservedBS ISO 12492:2012ISO 12492:2012(E)5.2 Analytical balance, capable of weighing to the nearest 0,0000 1 g.5.3 Micro-syr
37、inge, calibrated.5.4 Sample holder.Figure 1 Different components of coulometric Karl Fischer titration equipment6 Calibration6.1 Standardize the instrument using a traceable water standard (4.1) and determine the % water content to check the recovery.6.2 The test apparatus shall be calibrated in acc
38、ordance with the schedule given in Annex A.7 Sampling and preparation of test piece7.1 Take the laboratory sample in accordance with the method specified in ISO 1795 and prepare the test piece of 0,5 g to 1 g from the laboratory sample. Cut the test piece into small thin pieces using suitable tools
39、such as scissors or a knife.7.2 The test piece size should be small so that as many tests as possible can be carried out using the same electrolyte solution and the titration time can be kept short.8 Procedure8.1 Power onTurn on the power to the instrument as per the instructions of the instrument m
40、anufacturer. ISO 2012 All rights reserved 3BS ISO 12492:2012ISO 12492:2012(E)8.2 Selection of the generator electrodeThe generator electrode without diaphragm is the best choice for most applications. However, the generator electrode with diaphragm shall be used when samples contain ketone and aldeh
41、yde groups, because special reagents for aldehyde and ketone are only available for generator electrodes with diaphragms. If a low conductivity solvent like chloroform is used because of the solubility of the sample, then a generator electrode with a diaphragm is the first choice. Ensure safety prec
42、autions as per the equipment manual.8.3 Filling the electrolysis cell8.3.1 Generator electrode without diaphragmFill the cell with universal reagent (4.4) according to the instructions of the instrument manufacturer.8.3.2 Generator electrode with diaphragmFill the anode chamber and the cathode chamb
43、er with anode solution (4.2) and cathode solution (4.3) according to the instructions of the instrument manufacturer.8.4 Equipment check8.4.1 Reagent changeIn the following cases, the electrolyte solutions should be changed:a) when the capacity of the reagent is exhausted;b) if the drift is too high
44、;c) if during analysis the error message appears.8.4.2 Indicator electrode Clean the electrode according to the instruction of the instrument manufacturer.8.4.3 Cleaning8.4.3.1 Generator electrode with diaphragma) Sometimes resinous material is deposited on the diaphragm. Hang the generator electrod
45、e vertically from a support rod, fill with concentrated HNO3(4.8) and allow to stand overnight. Rinse the electrode with water and then with ethanol (4.7).b) If there is a deposition of oil on the electrode, wash the electrode with hexane (4.9) and then rinse with ethanol.c) To clean the diaphragm,
46、fill the cathode compartment of the generator electrode with methanol and allow it to drain out. Repeat this process two to three times.8.4.3.2 Generator electrode without diaphragmIf there is a deposition of oil on the electrode, wash the electrode with hexane (4.9) and then rinse it with ethanol (
47、4.7).Dry all parts thoroughly after cleaning. A hot-air blower can be used to dry the parts. If the parts are dried in an oven, care should be taken to ensure that the temperature does not exceed 70 C.4 ISO 2012 All rights reservedBS ISO 12492:2012ISO 12492:2012(E)8.4.4 Checking the instrument8.4.4.
48、1 The instrument can be checked with traceable water standard solutions with a water content of 1,00 mg/g 0,05 mg/g and/or 0,10 mg/g 0,01 mg/g. This is being done to check whether the instrument is working properly or not.8.4.4.2 When the instrument is stabilized and ready to operate, press the star
49、t switch and carefully inject a measured amount of the water standard (4.1) into the titration chamber using the calibrated micro-syringe (5.3). Record the reading when the analysis is completed. Generally, 1 g of water standard of water content of 1,00 mg/g 0,05 mg/g will give 1 mg of water.8.5 Analysis8.5.1 Stabilize the instrument for at least 30 min. During the stabilization period, the evaporator and reaction vessel of the instrument should be purged with dry nitrogen (water free) (4.5). The evaporator should
