1、BRITISH STANDARD BS EN ISO 3188:1994 Starches and derived products Determination of nitrogen content by the Kjeldahl method Titrimetric method The European Standard EN ISO 3188:1994 has the status of a British Standard UDC 664.2:546.17:543.24BSENISO3188:1994 This British Standard was published under
2、 the authorityofthe Standards Boardandcomes into effect on 15 November 1994 BSI 11-1999 The following BSI reference relates to the work on this standard: Draft announced in BSINews March 1993 ISBN 0 580 23180 1 Cooperating organizations The European Committee for Standardization (CEN), under whose s
3、upervision this European Standard 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 d
4、e normalisation Germany Deutsches 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 Netherlan
5、ds Nederlands Normalisatie-instituut Norway Norges Standardiseringsforbund Portugal Instituto Portugus da Qualidade Spain Asociacin Espaola de Normalizacin y Certificacin Sweden Standardiseringskommissionen i Sverige Switzerland Association suisse de normalisation United Kingdom British Standards In
6、stitution Amendments issued since publication Amd. No. Date CommentsBSENISO3188:1994 BSI 11-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii Foreword 2 1 Scope and field of application 3 2 References 3 3 Definition 3 4 Principle 3 5 Reagents 3 6 Apparatus 3 7 Pr
7、ocedure 3 8 Expression of results 4 9 Test report 5 National annex NA (informative) Cross-references Inside back coverBSENISO3188:1994 ii BSI 11-1999 National foreword This British Standard has been prepared under the direction of the BSI Standards Board and is the English language version of ENISO3
8、188:1994 Starch and derived products Determination of nitrogen content by the Kjeldahl method Titrimetric method, published by the European Committee for Standardization (CEN). It is identical with ISO3188:1978 Starch and derived products Determination of nitrogen content by the Kjeldahl method Titr
9、imetric method, published by the International Organization for Standardization (ISO). This British Standard 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 partici
10、pation in the preparation of EN ISO3188. Any queries relating to the EN should be directed to BSI. A British 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 d
11、oes not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, theEN ISO title page, pages 2 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had ame
12、ndments incorporated. This will be indicated in the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 3188 August 1994 UDC 664.2:546.17:543.24 Descriptors: Starches, chemical analysis, determination of content, nitrogen, volumetric analysis, Kjeldahl
13、method English version Starches and derived products Determination of nitrogencontent by the Kjeldahl method Titrimetric method (ISO 3188:1978) Amidons, fcules et produits drivs Dosagede lazote selon la mthode de Kjeldahl Mthode titrimtrique (ISO3188:1978) Strken und Strkederivate Bestimmung des Sti
14、ckstoffgehaltes nach dem Kjeldahl-Verfahren Volumetrisches Verfahren (ISO3188:1978) This European Standard was approved by CEN on1994-08-22. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a nati
15、onal standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in an
16、y 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 official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Icel
17、and, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and UnitedKingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1994 Copyright reserved to C
18、EN members Ref. No. EN ISO3188:1994 EENISO3188:1994 BSI 11-1999 2 Foreword The text of the International Standard ISO3188:1978, prepared by ISO/TC93, Starch, was submitted to the formal vote and was approved by CEN as EN ISO3188:1994 on1994-08-22 without any modifications. This European Standard sha
19、ll be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by February1995, and conflicting national standards shall be withdrawn at the latest by February1995. According to the CEN/CENELEC Internal Regulations, the following countries
20、are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, UnitedKingdom.ENISO3188:1994 BSI 11-1999 3 1 Scope and field of application This International S
21、tandard specifies a titrimetric method for the determination, by the Kjeldahl method, of the nitrogen content of starch and its derived products whose presumed nitrogen content is greater than0,01% (m/m). 1) NOTEIn starches and derived products to which nitrogenous materials have not been added, the
22、 nitrogen is present essentially in the form of protein and/or amino acids. 2 References ISO 1227/Add. 2, Starch, including derivatives and by-products Vocabulary. ISO 1871, Agricultural food products General directions for the determination of nitrogen by the Kjeldahl method. ISO 5378, Starches and
23、 derived products Determination of nitrogen content by the Kjeldahl method Spectrophotometric method. 3 Definition nitrogen content the value found using the procedure specified. It includes the nitrogen content of free amino acids, of compounds producing amino acids on hydrolysis and of ammonium co
24、mpounds. It does not include the nitrogen of nitrate and nitrite radicals, the nitrogen attached directly to another nitrogen atom or the nitrogen attached to an oxygen atom 4 Principle Destruction of organic matter by sulphuric acid in the presence of a compound catalyst 2) , alkalization of the re
25、action products, distillation of the liberated ammonia and collection in a boric acid solution, followed by titration with a standard volumetric sulphuric acid solution. 5 Reagents The reagents shall be of recognized analytical quality. Ammonia-free distilled water or water of at least equivalent pu
26、rity shall be used. 5.1 Sulphuric acid, concentrated, 20 1,84 g/ml 96 % (m/m). 5.2 Sodium hydroxide, solution30% (m/m), 201,33g/ml. NOTEThis solution may be more concentrated. 5.3 Boric acid,20 g/l solution. 3) 5.4 Compound catalyst 4) , consisting of, for example: potassium sulphate:97 g; copper(II
27、) sulphate, anhydrous:3 g. 5.5 Sulphuric acid, approximately0,02 N or0,1N standard volumetric solution. 5.6 Colorimetric indicator, prepared by mixing2parts by volume of a cold saturated solution of neutral methyl red in50% (V/V) ethanol with1 part by volume of a 0,25g/l solution of methylene blue i
28、n50% (V/V) ethanol. Store the indicator in a brown glass bottle. 6 Apparatus Usual laboratory equipment, and in particular 6.1 Kjeldahl flask, of suitable capacity, usually500 to 800ml, preferably with a ground glass joint, and provided with a pear-shaped glass bulb fitting loosely in the top of the
29、 neck of the flask. 6.2 Digestion stand, on which the Kjeldahl flask(6.1) can be heated in an inclined position in such a way that heat is applied only to that part of the flask wall which is below the liquid level at all stages. 6.3 Distillation or steam distillation apparatus, with a 200ml graduat
30、ed dropping funnel and an efficient splash head, the latter connecting the Kjeldahl flask(6.1) to the condenser. Any apparatus that satisfies the control tests given in ISO1871 is permitted. 6.4 Burette,25ml with0,05ml graduations, or10ml with0,01ml graduations. 6.5 Mechanical grinder or mortar. 6.6
31、 Sieve, with nominal mesh openings of0,6mm, complying with the requirements of ISO565. 6.7 Analytical balance 7 Procedure 7.1 Preparation of the test sample Mix the sample thoroughly and rapidly by shaking or stirring with a spatula in the sample container 5) . If the sample container is too small f
32、or this purpose, transfer the entire sample to another predried container of a suitable size to facilitate mixing. It may be necessary to grind the sample, in which case it shall all pass through the sieve (6.6) without leaving any residue. 1) For products whose presumed nitrogen content is less tha
33、n0,025% (m/m), see ISO5378. 2) See ISO1871. 3) For anticipated low nitrogen contents, a less concentrated solution may be needed in order to obtain greater accuracy. 4) See ISO1871, sub-clause 5.2. 5) In the case of glucose syrup, remove the surface layer (about5 mm) before mixing.ENISO3188:1994 4 B
34、SI 11-1999 7.2 Test portion Weigh, to the nearest0,001g, up to10g (mass m) ofthe test sample (7.1), according to the presumed nitrogen content, and transfer to the predried Kjeldahl flask (6.1), taking care that none of the product adheres to the inner wall of the neck of theflask. In the case of a
35、viscous liquid or a product in paste form, the test portion may be weighed in a small glass container or on a sheet of aluminium, paper or plastics which does not yield nitrogen, or whose nitrogen content is known, and which is left in the flask. In the case of a container which yields nitrogen, thi
36、s should be taken into account in the blank test (7.6). 7.3 Destruction of organic matter Add10g of the compound catalyst (5.4) and, using a suitable measuring cylinder, add the appropriate volume, in millilitres, of the concentrated sulphuric acid (5.1), calculated by the formula20 + 4 m, in such a
37、 way that the acid rinses the inner wall of theneck of the flask. Mix the contents of the flask by swirling the flask gently until the mixture is free from lumps and the test portion is completely wetted. In order to avoid super-heating, add a boiling aid (for example glass beads). Insert the pear-s
38、haped glass bulb (see 6.1) in the neck of the flask and place it in an inclined position on the digestion stand (6.2). Heat with care until the liquid in the flask boils gently. Continue to heat for1h after the liquid becomes clear. In the case of digestion apparatus heated by gas, ensure that the f
39、lame does not extend beyond the part of the flask filled with liquid, in order to avoid loss of nitrogen. 7.4 Distillation and titration Allow the contents of the flask to cool and rinse the pear-shaped glass bulb and the inner neck of the flask with a few millilitres of water, allowing the rinsings
40、 to run into the flask. Add, with care, between50 and200ml of water (according to the apparatus used), whilst swirling the contents of the flask. Connect the flask to the distillation or steam distillation apparatus (6.3), previously freed from ammonia by steaming. Adjust the lower end of the conden
41、ser so that it just touches the bottom of a500ml conical flask containing a known volume (varying between25 and50ml) of the boric acid solution (5.3) and3 to5 drops of the titration indicator (5.6). Render the digestion liquid alkaline by slowly adding, through the graduated separating funnel (see 6
42、.3) placed in the neck of the flask, between150 and 200ml of the sodium hydroxide solution (5.2), ensuring that the stem of the funnel does not become empty. Mix well, then turn on the condenser water and start heating; the ammonia then begins to be carried over. The indicator contained in the flask
43、 turns immediately to its alkaline colour. During distillation, ensure that steam generation is kept constant. Distillation is complete when200ml of liquid have been collected in20 to30 min. Turn off the heat and lower the conical flask. Allow the condenser to drip for a few minutes into the flask a
44、nd rinse the tip of the condenser with water, collecting the rinsings in the conical flask. The liquid contained in the flask should be green. Titrate the contents of the flask with either0,02N or0,1N sulphuric acid solution (5.5), using a10ml or25ml burette (6.4) as appropriate, until the colour of
45、 the contents turns reddish violet. 7.5 Number of determinations Carry out two determinations on the same test sample (7.1). 7.6 Blank test Carry out a blank test on the reagents only. If the test portion has been weighed in a container which yields nitrogen (see 7.2), carry out the blank test using
46、 an identical container. 7.7 Check tests Carry out the check tests specified in ISO1871. 8 Expression of results The nitrogen content is given, as a percentage by mass, by the formula where T is the normality of the sulphuric acid solution(5.5) used in the two titrations; V 0 is the volume, in milli
47、litres, of the sulphuric acid solution used in the blank test (7.6); V 1 is the volume, in millilitres, of the sulphuric acid solution used in the determination (7.4); m is the mass, in grams, of the test portion(7.2). 0,014 01T V 1 V 0 () 100 m - 1,401 T V 1 V 0 () m - =ENISO3188:1994 BSI 11-1999 5
48、 Express the result as the arithmetic mean of the two determinations if the volumes of the sulphuric acid solution used do not differ by more than0,1ml. Otherwise, repeat the determinations on the same test sample. 9 Test report The test report shall indicate the method used and the results obtained
49、. It shall also mention all operating conditions that are not specified in this International Standard, or are regarded as optional, as well as any circumstances that may have influenced the results. The test report shall include all details required for complete identification of the sample.6 blankBSENISO3188:1994 BSI 11-1999 National annex NA (informative) Cross-reference Publication referred to Corresponding British Standard ISO5378:1978 BS E
