1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 12779:2011Lactose Determination ofwater content Karl FischermethodBS EN ISO 12779:2013BS EN ISO 12779:2013 BRITISH STANDARDNational forewordThis British Standard is the UK
2、 implementation of EN ISO 12779:2013. It is identical to ISO 12779:2011. It supersedes BS ISO 12779:2011, which is withdrawn.The UK participation in its preparation was entrusted to Technical Committee AW/5, Chemical analysis of milk and milk products.A list of organizations represented on this comm
3、ittee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2013. Published by BSI Standards Limited 2013.ISBN 978 0 580 79331 8ICS 67.1
4、00.99Compliance with a British Standard cannot confer immunity from legal obligations.This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 December 2011.Amendments/corrigenda issued since publicationDate Text affected30 June 2013 This corrigend
5、um renumbers BS ISO 12779:2011 as BS EN ISO 12779:2013EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 12779 May 2013 ICS 67.100.99 English Version Lactose - Determination of water content - Karl Fischer method (ISO 12779:2011) Lactose - Dtermination de la teneur en eau - Mthode de Karl Fisc
6、her (ISO 12779:2011) Lactose - Bestimmung des Wassergehaltes - Karl-Fischer-Verfahren (ISO 12779:2011) This European Standard was approved by CEN on 16 May 2013. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
7、 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 CEN-CENELEC Management Centre or to any CEN member. This European Standard exists in three official versions (English, F
8、rench, 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 CEN-CENELEC Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgar
9、ia, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turk
10、ey and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2013 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN I
11、SO 12779:2013: EEN ISO 12779:2013 (E) 3 Foreword The text of ISO 12779:2011 has been prepared by Technical Committee ISO/TC 34 “Food products” of the International Organization for Standardization (ISO) and has been taken over as EN ISO 12779:2013 by Technical Committee CEN/TC 302 “Milk and milk pro
12、ducts - Methods of sampling and analysis” the secretariat of which is held by NEN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by November 2013, and conflicting national standards shall be withdr
13、awn at the latest by November 2013. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. According to the CEN-CENELEC Internal Regulations,
14、 the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, La
15、tvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. Endorsement notice The text of ISO 12779:2011 has been approved by CEN as EN ISO 12779:2013 without any modification. BS EN ISO 12779:201
16、3EN ISO 12779:2013 (E)BS ISO 12779:2011INTERNATIONAL STANDARD ISO 12779:2011(E)IDF 227:2011(E) ISO and IDF 2011 All rights reserved 1Lactose Determination of water content Karl Fischer method 1 Scope This International Standard specifies a method for the determination of the water content of lactose
17、 by Karl Fischer (KF) titration. 2 Principle The test sample is directly titrated with a commercially available two-component Karl Fischer reagent. The water content is calculated from the amount of reagent used. Titration at a temperature of approximately 40 C gives shorter titration times and shar
18、per end points. Only at this or higher temperatures is the use of a one-component Karl Fischer reagent (3.1) recommended. 3 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and only distilled or demineralized water or water of equivalent purity. Avoid absorption
19、 of moisture from the environment. 3.1 Karl Fischer (KF) reagent1). The KF reagent is a commercially available pyridine-free two-component reagent consisting of a titration component (3.2) and a solvent component (3.3). The titration component (3.2) is a methanolic solution of iodine and the solvent
20、 component (3.3) is a methanolic solution of sulfur dioxide and an appropriate base (e.g. imidazole). Alternatively, a pyridine-free one-component KF reagent can also be used which only consists of a titration component. The titration component (3.2) is a solution of iodine, sulfur dioxide and an ap
21、propriate base (e.g. imidazole) in a suitable solvent (e.g. diethylene glycol monoethyl ether). The solvent component (3.3) is methanol (3.5). This combination of a one-component titration reagent and methanol is only recommended if the titration is carried out at a temperature of approximately 40 C
22、 or higher. 3.2 Titration component. The titration component of the KF reagent (3.1) shall have a water equivalent of approximately 2 mg/ml of water. A KF reagent with a water equivalent of approximately 5 mg/ml of water is also possible if a KF apparatus with a burette of capacity 5 ml is used (4.1
23、). 3.3 Solvent component. The solvent component of the KF reagent as specified in 3.1. 3.4 Water standard, w(H2O) = 10 mg/g. 1) Hydranal-Titrant 2/Hydranal-Solvent from Sigma-Aldrich and apuraTitrant 2/apuraSolvent from Merck are examples of commercially available two-component systems. Hydranal-Com
24、posite 2 from Sigma-Aldrich and apuraCombiTitrant 2 from Merck are examples of commercially available one-component reagents. This information is given for the convenience of users of this document and does not constitute an endorsement by ISO and IDF of these products. BS EN ISO 12779:2013ISO 12779
25、:2011(E)BS ISO 12779:2011ISO 12779:2011(E) IDF 227:2011(E) 2 ISO and IDF 2011 All rights reservedFor the determination of the water equivalent of the titration component, use a commercially available liquid water standard containing 10 mg/g of water. 3.5 Methanol (CH3OH), with a mass fraction of wat
26、er of not more than 0,05 %. 4 Apparatus Usual laboratory apparatus and, in particular, the following. Equipment shall be completely dry when used. 4.1 Karl Fischer (KF) apparatus. Use an automatic volumetric KF apparatus, preferably with a burette of capacity 10 ml. The burette should be of capacity
27、 5 ml if a KF reagent with a water equivalent of approximately 5 mg/ml of water is used (see 3.2). For quicker titrations at approximately 40 C, use a double-jacketed titration vessel with a water inlet and outlet to carry out the titration. 4.2 Water bath, capable of maintaining a water temperature
28、 of 40 C 5 C under thermostatic control, with a pump for heating the double-jacketed titration vessel of the KF apparatus (4.1). NOTE The use of a water bath with thermostatic control is only necessary if the titrations are carried out at temperatures above room temperature. 4.3 Analytical balance,
29、capable of weighing to the nearest 1 mg, with a readability of 0,1 mg. 4.4 Disposable syringes, of capacity 5 ml or 10 ml, for quantifying the water standard (3.4). 4.5 Glass weighing spoon, for dosing the test sample. 5 Sampling A representative sample should have been sent to the laboratory. It sh
30、ould 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 is given in ISO 707 IDF 501. 6 Procedure 6.1 KF apparatus drift 6.1.1 Determine the drift of the KF apparatus (4.1) every day
31、and/or when the working conditions change as follows. Add to the titration vessel of the KF apparatus (4.1) approximately 30 ml of solvent component (3.3). Pre-titrate the solvent component. Then carry out a titration over 5 min (without addition of a test sample). If determinations (6.5) are carrie
32、d out at 40 C, heat the vessel and its contents using the water bath (4.2) to 40 C before pre-titrating the solvent component and carrying out the titration without addition of a test sample. IMPORTANT During each titration, the amount of solvent component used shall completely cover the electrodes
33、of the KF apparatus. BS EN ISO 12779:2013ISO 12779:2011(E)BS ISO 12779:2011ISO 12779:2011(E) IDF 227:2011(E) ISO and IDF 2011 All rights reserved 36.1.2 Calculate the KF apparatus drift, qV, in millilitres per minute, by using Equation (1): dVVqt (1) where Vdis the volume, in millilitres, of the tit
34、ration component (3.2) in the titration (6.1.1); t is the numerical value, in minutes, of the time. Alternatively, calculate the KF apparatus drift, qm, in milligrams of water per minute, by using Equation (2): demVqt (2) where eis the water equivalent (6.2) of the titration component (3.2), in mill
35、igrams of water per millilitre, used in the titration (6.1.1). 6.2 Water equivalent of the titration component of the KF reagent 6.2.1 Titration To calculate the water equivalent of the titration component, e, accurately carry out the titration in this subclause and the calculation step (6.2.2) five
36、 times. Add approximately 30 ml solvent component (3.3) to the titration vessel of the KF apparatus (4.1) (see also 6.1.1) and pre-titrate the solvent component. NOTE The water equivalent of the titration component does not depend on temperature. It is therefore not necessary to heat the titration v
37、essel for water equivalent determinations. If determinations (6.5) are carried out at 40 C, the water equivalent can also be determined at 40 C. In that case, the vessel and its contents are heated to 40 C using the water bath (4.2) before carrying out titrations. Into a disposable syringe (4.4), ta
38、ke up between 0,6 g to 0,9 g of the water standard (3.4) (an amount of between 6 mg and 9 mg water). Weigh the syringe and its contents, recording the mass to the nearest 0,1 mg. It is also possible to take up more than 0,6 g to 0,9 g of the water standard and to use the same contents of the syringe
39、 for several titrations, but it is then important to carry out the titrations immediately one after the other. In this case, approximately 0,6 g to 0,9 g of the water standard should also be used for each titration, the exact amount being calculated each time by weighing the syringe and its remainin
40、g contents after each injection. NOTE Only for very experienced laboratories is it possible to use a small amount (approximately one drop from a syringe) of pure water instead of a commercial water standard. Even slight weighing errors lead to massive deviations of the result since they have an effe
41、ct of 100 %. Add the amount of water standard in the syringe to the titration vessel. Weigh the empty syringe again, recording its mass to the nearest 0,1 mg. Subtract the mass of the empty syringe from that of the syringe with the water standard before addition of the water standard to the vessel t
42、o obtain the net mass of the water standard added to the titration vessel. Record the net mass, , to the nearest 0,1 mg, of added water standard for each titration (i = 1 5). 2HOimCarry out a titration while using as shut-off criterion the 10 s stop delay time mentioned in 6.3. Record, for i = 1 5,
43、the volume, , in millilitres, of the titration component used. e,iVBS EN ISO 12779:2013ISO 12779:2011(E)BS ISO 12779:2011ISO 12779:2011(E) IDF 227:2011(E) 4 ISO and IDF 2011 All rights reservedDo not perform more than three titrations on one portion of solvent component. After three titrations on on
44、e portion, empty the titration vessel and carry out further titrations by again adding to the titration vessel of the KF apparatus approximately 30 ml solvent component, pre-titrating the solvent component and proceeding in the same way as before. 6.2.2 Calculation Calculate the water equivalent of
45、the titration component, e,i, in milligrams of water per millilitre, by using Equation (3): 22e,HO HO,e,iisimwV (3) where 2HOim is the mass, in grams, of the water standard used for titration i (6.2.1); 2H O,sw is the water mass fraction, in milligrams per gram, of the water standard; e,iVis the vol
46、ume, in millilitres, of the titration component (3.2) in titration i (6.2.1). 6.2.3 Mean value Calculate the water equivalent of the titration component, e, expressed in milligrams of water per millilitre, as the mean value of the five (i = 1 5) single titrations (6.2.1) by using Equation (4): 5e,1e
47、5ii(4) 6.2.4 Expression of water equivalents Express the (mean) value of the water equivalent of the titration component to three decimal places. 6.3 Shut-off criterion According to the features of the apparatus used, the stop criterion shall either be a stop delay time of 10 s or a stop drift sligh
48、tly above the measured drift (6.1). 6.4 Preparation of the test sample Homogenize the test sample by mixing the powder thoroughly. 6.5 Determination Add approximately 30 ml of solvent component (3.3) to the titration vessel of the KF apparatus (4.1). If a one-component KF reagent is used (3.1) or if
49、 shorter titration times are preferred, heat the vessel and its contents using the water bath (4.2) to approximately 40 C. Charge a glass weighing spoon (4.5) with approximately 0,3 g test sample (6.4). Weigh the spoon and the test portion, recording the mass to the nearest 0,1 mg. BS EN ISO 12779:2013ISO 12779:2011(E)BS ISO 12779:2011ISO 12779:2011(E) IDF 227:2011(E) ISO and IDF 2011 All rights reserved 5Add the test portion to the titration vessel by quickly opening and closing the septum stopper. Weigh
