1、BRITISH STANDARD BS EN ISO 5381:1994 Starch hydrolysis products Determination of water content ModifiedKarl Fischer method The European Standard EN ISO5381:1994 has the status of a British Standard UDC664.2:543.812BSENISO5381:1994 This British Standard was published under the authority ofthe Standar
2、ds Board and comesinto effect on 15November1994 BSI12-1999 The following BSI reference relates to the work on this standard: Draft announced in BSINews March1993 ISBN 0 580 23187 9 Cooperating organizations The European Committee for Standardization (CEN), under whose supervision this European Stand
3、ard was prepared, comprises the national standards organizations of the following countries: Austria Oesterreichisches Normungsinstitut Belgium Institut belge de normalisation Denmark Dansk Standard Finland Suomen Standardisoimisliito, r.y. France Association franaise de normalisation Germany Deutsc
4、hes Institut fr Normung e.V. Greece Hellenic Organization for Standardization Iceland Technological Institute of Iceland Ireland National Standards Authority of Ireland Italy Ente Nazionale Italiano di Unificazione Luxembourg Inspection du Travail et des Mines Netherlands Nederlands Normalisatie-ins
5、tituut Norway Norges Standardiseringsforbund Portugal Instituto Portugus da Qualidade Spain Asociacin Espaola de Normalizacin y Certificacin Sweden Standardiseringskommissionen i Sverige Switzerland Association suisse de normalisation UnitedKingdom British Standards Institution Amendments issued sin
6、ce publication Amd. No. Date CommentsBSENISO5381:1994 BSI 12-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii Foreword 2 0 Introduction 3 1 Scope and field of application 3 2 Reference 3 3 Principle 3 4 Reactions 3 5 Reagents 3 6 Apparatus 3 7 Procedure 4 8 Expr
7、ession of results 5 9 Test report 5 Annex A Special syringe for adding samples in the form ofviscousliquidsanditsmethod of use 6 Annex B Illustrations of Karl Fischer apparatus 7 Figure 1 Special syringe 6 Figure 2 General arrangement 7 Figure 3 Platinum electrodes 8 Figure 4 Circuit for the device
8、for the electrometric detection of the end point 9BSENISO5381:1994 ii BSI 12-1999 National foreword This British Standard has been prepared under the direction of the BSI Standards Board and is the English language version of EN ISO5381:1994 Starch hydrolysis products Determination of water content
9、Modified Karl Fischer method, published by the European Committee for Standardization (CEN). It is identical with ISO5381:1983 Starch hydrolysis products Determination of water content Modified Karl Fischer method, published by theInternational Organization for Standardization (ISO). This British St
10、andard has been produced to fulfil BSIs obligation to publish all approved European Standards but, because of the absence of interest in the UK in the subject concerned, there has been no UK participation in the preparation of EN ISO5381. Any queries relating to the EN should be directed to BSI. A B
11、ritish 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 itself confer immunity from legal obligations. Summary of pages This document comprises a f
12、ront cover, an inside front cover, pagesi andii, theEN ISO title page, pages2 to9 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.EUROPEAN STANDARD NORME EUROPENNE
13、EUROPISCHE NORM EN ISO5381 August1994 UDC664.2:543.812 Descriptors: Carbohydrates, starches, food starch, tests, determination of content, water, Karl Fischer reagent, test equipment English version Starch hydrolysis products Determination of water content Modified Karl Fischer method (ISO5381:1983)
14、 Produits dhydrolyse de lamidon ou de la fcule Dosage de leau Mthode Karl Fischer modifie (ISO5381:1983) Strkehydrolysenprodukte Bestimmung des Wassergehalts Modifiziertes Karl-Fischer-Verfahren (ISO5381:1983) This European Standard was approved by CEN on1994-08-22. CEN members are bound to comply w
15、ith the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secreta
16、riat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officia
17、l versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and UnitedKingdom. CEN European Committee for Standardization Comit Europen de Norm
18、alisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1994 Copyright reserved to CEN members Ref. No. EN ISO5381:1994 EENISO5381:1994 BSI 12-1999 2 Foreword The text of the International Standard ISO5381:1983, prepared by ISO/TC93, Starch, was submitted to
19、 the formal vote and was approved by CEN as EN ISO5381:1994 on 1994-08-22 without any modifications. This European Standard shall be given the status ofa national standard, either by publication of an identical text or by endorsement, at the latest by February1995, and conflicting national standards
20、 shall be withdrawn at the latest by February1995. According to the CEN/CENELEC Internal Regulations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal
21、, Spain, Sweden, Switzerland, UnitedKingdom.ENISO5381:1994 BSI 12-1999 3 0 Introduction This International Standard is based on the method described in ISO760. However, it has been improved by determining the content directly using the methanol/formamide solvent. 1 Scope and field of application Thi
22、s International Standard specifies a method for the determination of the water content of starch hydrolysis products. 2 Reference ISO760, Determination of water Karl Fischer method (General method). 3 Principle Reaction of a solution of iodine, sulphur dioxide, pyridine and2-methoxyethanol (stabiliz
23、ed Karl Fischer reagent) with the water contained in the product dispersed previously in a mixture of methanol and formamide. 4 Reactions H 2 O+I 2 +SO 2+3C 5 H 5 N F 2C 5 H 5 N.HI + C 5 H 5 N.SO 3 C 5 H 5 N.SO 3 +ROH F C 5 H 5 NH.OSO 2 OR where R is the 2-methoxyethyl radical. 5 Reagents During the
24、 analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity; all solvents shall have a water content of less than0,1%(m/m). 5.1 “Stabilized” Karl Fischer reagent The stabilized reagent is commercially available in the form of a prepared solution
25、. It is also possible to prepare the reagent in the laboratory(seeISO760). 5.2 Methanol/formamide solvent Mix700ml of anhydrous methanol with300ml of anhydrous formamide. This reagent shall be handled with care. 5.3 Sodium tartrate, crystalline (Na 2 C 4 H 4 O 6 .2H 2 O) This product is commercially
26、 available in the form “special quality for Karl Fischer”. If this quality cannot be obtained, wash the tartrate with10ml of the methanol/formamide solvent(5.2), and carry out an appropriate blank test. Crush the product so that it passes completely through a sieve of nominal aperture size2504m, com
27、plying with the requirements of ISO565. The water content of this hydrate is approximately15,66%(m/m) and shall be checked by vacuum drying at150 C until constant mass is obtained. 6 Apparatus Ordinary laboratory apparatus, in particular 6.1 One-mark pipette, of capacity20ml. 6.2 Devices, into which
28、 the sample to be analysed can be introduced. 6.2.1 Weighing tube (for solid products), consisting of a test tube of suitable diameter so as to allow the introduction of samples, and fitted with a stopper. 6.2.2 Syringe (for viscous liquids), of capacity10ml, for example in accordance with Annex A.
29、6.2.3 One-mark pipettes (for liquid products), of appropriate capacities. 6.3 Karl Fischer titrating equipment or similar apparatus (see the illustrations in Annex B) 6.4 Analytical balanceENISO5381:1994 4 BSI 12-1999 7 Procedure 7.1 Preparation of the apparatus The reagents shall be standardized fo
30、r each daily series of tests and the apparatus set up in conformity with the manufacturers instructions. If the apparatus has remained assembled for more than24h, it is recommended that the reagent be poured back into the tank and that the burette be filled several times before commencing a series o
31、f titrations. If the titration vessel of the apparatus has not been used before, or after emptying, pour in20ml of the methanol/formamide solvent(5.2) either by means of a pipette fitted with a bulb(6.1), or by means of the device fitted in the apparatus used. This quantity should be adequate for im
32、mersing the ends of the platinum electrodes having adjusted the position of these electrodes in such a way as not to obstruct the stirrer during its rotation. Adjust the rate of stirring and add the Karl Fischer reagent(5.1) until the equivalence point is reached and maintained for a period of60s(se
33、e7.3). Successive samples to be analysed can be added to the liquid remaining in the titration vessel. When the vessel is full, empty it by means of suction using a siphon tube introduced through the circular aperture in the cover or through the valve at the bottom of the vessel. 7.2 Standardization
34、 of the Karl Fischer reagent Weigh, to the nearest0,5mg, approximately500 to700mg of the sodium tartrate(5.3) (according to the type of apparatus) in the weighing tube(6.2.1) and introduce it into the titration vessel. Weigh the tube again to determine the exact mass(m 0 ) of sodium tartrate introdu
35、ced. Leave for3 min to allow the sodium tartrate to dissolve. Then titrate using the Karl Fischer reagent(5.1) until the equivalence point is reached again, as in7.1 (seethe notes to7.4.3.3). Note the volume(V 0 ) of reagent used. Repeat the determination until two successive titrations agree to at
36、least0,2% of the mean. 7.3 Correction The dispersion of the samples and the extraction of the water contained in the samples takes time and the value of the titre can change during this period. This is why it is necessary to make a correction taking into account this change by taking the same time f
37、or standardizing the reagent. 7.4 Determination 7.4.1 Preparation of the test sample 7.4.1.1 Liquid or viscous products Mix the laboratory sample. If necessary, warm slightly to obtain a homogeneous mixture. 7.4.1.2 Solid products Crush the laboratory sample so that it passes easily through a sieve
38、of nominal aperture size5004m, complying with the requirements of ISO565. 7.4.2 Test portion 7.4.2.1 Liquid or viscous products Using a pipette(6.2.3) or a special syringue(6.2.2), take a quantity of the test sample(7.4.1.1) so that a volume of approximately20ml of the Karl Fischer reagent is necess
39、ary when using a25ml burette, corresponding to approximately120mg of water. 7.4.2.2 Solid products In the weighing tube(6.2.1), weigh, to the nearest0,1mg, a quantity of the test sample(7.4.1.2) so that a volume of approximately20ml of the Karl Fischer reagent is necessary when using a25ml burette.
40、7.4.3 Titration 7.4.3.1 Place the test portion(7.4.2) into the titration vessel as quickly as possible and determine the exact mass added in the case of solid products or viscous liquids by reweighing the weighing tube or syringe. 7.4.3.2 Switch on the stirrer and stir until the sample is completely
41、 dispersed so as to allow total extraction of the water. Note the time necessary for obtaining good dispersion.ENISO5381:1994 BSI 12-1999 5 7.4.3.3 Titrate with the Karl Fischer reagent(5.1) as indicated in7.1 until the equivalence point is reached. NOTE 1The Karl Fischer reagent has a very dark col
42、our. It is recommended that the graduations of the burette be read at the top of the column of liquid and not at the bottom of the meniscus. NOTE 2If an automatic apparatus is used, the burette is filled so that the bottom of the meniscus is at the same level as the burette graduation. Therefore, it
43、 is necessary to add0,1ml to each reading to take this into account. 7.4.4 Number of determinations Carry out two determinations on the same test sample(7.4.1). 8 Expression of results 8.1 Method of calculation and formulae 8.1.1 Water equivalent of the Karl Fischer reagent The water equivalent, T,
44、of the Karl Fischer reagent, expressed in milligrams of water per millilitre of reagent, is given by the formula where m 0 is the mass, in milligrams, of the sodium tartrate(5.3) used for the standardization(7.2); H is the water content, expressed as a percentage by mass, of the sodium tartrate used
45、, determined according to5.3; V 0 is the volume, in millilitres, of the Karl Fischer reagent used for the standardization(7.2). 8.1.2 Water content of the product The water content, expressed as a percentage by mass, is given by the formula where V is the volume, in millilitres, of the Karl Fischer
46、reagent used for the titration(7.4.3); m is the mass, in milligrams, of the test portion(7.4.2); 1) T is the water equivalent, expressed in milligrams per millilitre, of the Karl Fischer reagent, determined according to8.1.1. Take as the result the arithmetic mean of the two determinations provided
47、that the requirement for repeatability(see8.2) is satisfied. 8.2 Repeatability The difference between the results of two determinations carried out simultaneously or in rapid succession on the same sample by the same analyst shall not exceed: 0,05 for water contents less than1%(m/m); 0,1 for water c
48、ontents between1 and10%(m/m); 0,15 for water contents between10 and20%(m/m); 0,2 for water contents greater than20%(m/m). 9 Test report The test report shall show the method used and the result obtained, clearly indicating the method of expression used. It shall also mention any operating details no
49、t specified in this International Standard, or regarded as optional, as well as any circumstances likely to have influenced the results. The test report shall give all the details required for the complete identification of the sample. 1) For liquid products, this mass is equal to the volume of the sample taken by pipette multiplied by its density. m 0 H 100 V 0 - V T 100 m -ENISO5381:1994 6 BSI 12-1999 Annex A Special syringe for adding samples in
