1、BRITISH STANDARD BS EN ISO 5378:1994 Starches and derived products Determination of nitrogen content by the Kjeldahl method Spectrometric method The European Standard EN ISO5378:1994 has the status of a British Standard UDC664.2:543.846:543.42BSENISO5378:1994 This British Standard was published unde
2、r the authority ofthe Standards Board and comes into effect on 15November1994 BSI12-1999 The following BSI reference relates to the work on this standard: Draft announced in BSI News March1993 ISBN 0 580 23186 0 Cooperating organizations The European Committee for Standardization (CEN), under whose
3、supervision 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
4、de 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 Netherla
5、nds 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 I
6、nstitution Amendments issued since publication Amd. No. Date CommentsBSENISO5378:1994 BSI 12-1999 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 P
7、rocedure 4 8 Expression of results 5 9 Test report 5 National annex NA (informative) Cross-reference Inside back coverBSENISO5378:1994 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 ISO
8、5378:1994 Starches and derived products Determination of nitrogen content by the Kjeldahl method Spectrophotometric method, published by the European Committee for Standardization (CEN). It is identical with ISO5378:1978 Starches and derived products Determination of nitrogen content by the Kjeldahl
9、 method Spectrophotometric 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
10、 been no UK participation in the preparation of EN ISO5378. 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
11、 British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, theENISO title page, pages2 to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and ma
12、y have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO5378 August1994 UDC664.2:543.846:543.42 Descriptors: Food products, starches, chemical analysis, determination of content, nitrogen, spe
13、ctrophotometric analysis English version Starches and derived products Determination of nitrogencontent by the Kjeldahl method Spectrophotometric method (ISO5378:1978) Amidons, fcules et produits drivs Dosagede lazote selon la mthode de Kjeldahl Mthode spectrophotomtrique (ISO5378:1978) Strke und St
14、rkederivate Bestimmung des Stickstoffgehalts nach dem Kjeldahl-Verfahren Spektrometrisches Verfahren (ISO5378:1978) 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 Europe
15、an 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 Secretariat or to any CEN member. This European Standard exists in three official versions (English,
16、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 official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finlan
17、d, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland andUnited Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Bruss
18、els 1994 Copyright reserved to CEN members Ref. No. EN ISO5378:1994 EENISO5378:1994 BSI 12-1999 2 Foreword The text of the International Standard ISO5378:1978, prepared by ISO/TC93, Starch, was submitted to the formal vote and was approved by CEN as EN ISO5378:1994 on1994-08-22 without any modificat
19、ions. 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 February1995, and conflicting national standards shall be withdrawn at the latest by February1995. According to the CEN/CENELEC Internal Regul
20、ations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, United Kingdom.ENISO5378:1994 BSI 12-1999 3 1 Scope and field of
21、 application This International Standard specifies a spectrophotometric method for the determination, by the Kjeldahl method, of the nitrogen content of starch and its derived products whose presumed nitrogen content is less than0,025% (m/m). 1) NOTEIn starches and their derived products to which ni
22、trogenous materials have not been added, the nitrogen is present essentially in the form of protein and/or amino acids. 2 References ISO1227/Add.2, Starch, including derivatives and by-products Vocabulary, Addend. ISO1871, Agricultural food products General directions for the determination of nitrog
23、en by the Kjeldahl method. ISO3188, Starches and derived products Determination of nitrogen content by the Kjeldahl method Titrimetric method. 3 Definition nitrogen content the value found using the procedure specified. It includes the nitrogen content of free amino acids, of compounds producing ami
24、no acids on hydrolysis and of ammonium compounds. 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 comp
25、ound catalyst 2) , alkalization of the reaction products, distillation of the liberated ammonia and collection in a sulphuric acid solution, followed by spectrophotometry, of the ammonium salt formed after the addition of the Nessler reagent. 5 Reagents The reagents shall be of recognized analytical
26、 quality. Ammonia-free distilled water or water of at least equivalent purity shall be used. 5.1 Sulphuric acid, concentrated, 20 1,84g/ml96% (m/m). 5.2 Sodium hydroxide, solution30% (m/m), 20 1,33g/ml. NOTEThis solution may be more concentrated. 5.3 Compound catalyst 3) , consisting of, for example
27、 potassium sulphate:97g; copper(II) sulphate, anhydrous:3g. 5.4 Ammonium sulphate, ammonium oxalate or ammonium chloride 5.5 Sulphuric acid, approximately0,1N standard volumetric solution. 5.6 Nessler reagent, prepared as follows at least2days before use: Dissolve100g of mercury(II) iodide and70g of
28、 potassium iodide in100ml of water. Dissolve224g of potassium hydroxide in700ml of water in a1000ml one-mark volumetric flask and allow to cool to ambient temperature. Add the mercury(II) iodide/potassium iodide solution slowly, with stirring, to the potassium hydroxide solution. Dilute to the mark
29、with water and mix. Allow to stand for at least2days before using. NOTEThe reagent should be kept in a brown glass bottle. If it is kept in an air-tight bottle and in the shade, it can be used even after1year if care is taken to leave the sediments undisturbed when it is re-used. 6 Apparatus Usual l
30、aboratory equipment and, in particular: 6.1 Kjeldahl flask, of suitable capacity, usually500 to800ml, preferably with a ground glass joint, and provided with a pear-shaped glass bulb fitting loosely in the top of the neck of the flask. 6.2 Digestion stand, on which the Kjeldahl flask(6.1) can be hea
31、ted 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 a200ml graduated dropping funnel and an efficient splash head, the latter connecting the Kjeldahl f
32、lask(6.1) to the condenser. Any apparatus that satisfies the control tests given in ISO1871 is permitted. 6.4 Conical flasks, capacity100ml. 6.5 One-mark volumetric flask, capacity200ml, with a plain neck, complying with the requirements of ISO1042, class A. 6.6 Pipettes, of suitable capacity, compl
33、ying with the requirements of ISO648, class A. 6.7 Spectrophotometer, capable of being adjusted at a wavelength of430nm and provided with appropriate cells whose optical path length shall be stated in the test report. 1) For products whose presumed nitrogen content is greater than0,01% (m/m), see IS
34、O3188. 2) See ISO1871. 3) See ISO1871. sub-clause5.2.ENISO5378:1994 4 BSI 12-1999 6.8 Mechanical grinder or mortar 6.9 Sieve, with a nominal mesh opening of0,6mm, complying with the requirements of ISO565. 6.10 Analytical balance 7 Procedure 7.1 Preparation of the test sample Mix the sample thorough
35、ly and rapidly by shaking or stirring with a spatula in the sample container 4) . If the sample container is too small for 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 must pa
36、ss through the sieve(6.9) without leaving any residue. 7.2 Test portion Weigh, to the nearest0,001g,2 to5g (mass m 0 ) of the 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
37、 of the neck of the flask. In the case of a 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 ca
38、se of a container which yields nitrogen, this should be taken into account in the blank test(7.8). 7.3 Destruction of organic matter Add3g of the compound catalyst(5.3) and, using a suitable measuring cylinder, add the appropriate volume, in millilitres, of the concentrated sulphuric acid(5.1), calc
39、ulated by the formula20+4m 0 , in such a way that the acid rinses the inner wall of the neck 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 (fo
40、r example glass beads). Insert the pear-shaped glass bulb (see6.1) 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 app
41、aratus heated by gas, ensure that the flame does not extend beyond the part of the flask filled with liquid, in order to avoid loss of nitrogen. 7.4 Distillation 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 wat
42、er, allowing the rinsings to run into the flask. Add, with care, between50 and150ml 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
43、 lower end of the condenser so that it just touches the bottom of the one-mark volumetric flask(6.5), containing25ml of the sulphuric acid solution(5.5). Render the digestion liquid alkaline by slowly adding, through a graduated separating funnel (see6.3) placed in the neck of the flask,120ml of the
44、 sodium hydroxide solution(5.2), ensuring that the neck 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. During distillation ensure that steam generation is kept constant. Distillation is complete when abou
45、t150ml of liquid have been collected in20 to30min. Turn off the heat and lower the conical flask. Allow the condenser to drip for a few minutes into the flask and rinse the tip of the condenser with water, collecting the rinsings in the conical flask. Dilute to the mark with water and mix. 7.5 Prepa
46、ration of the calibration curve Prepare a suitable series of standard matching solutions containing at least five different and known concentrations of an ammonium salt(5.4). Using the pipette(6.6), transfer50ml of each of these standard solutions into a series of separate100ml conical flasks(6.4) a
47、nd50ml of water into another one-mark100ml conical flask(6.4). The last mentioned corresponds to a zero concentration of the ammonium salt for the calibration curve. Add by pipette1,0ml of the Nessler reagent(5.6) to each flask and mix separately. Allow to stand for10min and measure the absorbance o
48、f each of these solutions, using the spectrophotometer(6.7) adjusted at a wavelength of430nm. Plot the calibration curve showing the absorbance as a function of the number of micrograms of nitrogen. NOTE 1Between0 and2404g of nitrogen for50ml (about0 to50004g of nitrogen for1000ml) of solution the c
49、alibration curve is a straight line. 4) In the case of glucose syrup, remove the surface layer (about5mm) before mixing.ENISO5378:1994 BSI 12-1999 5 NOTE 2Each point on the calibration graph should be the arithmetic mean of two determinations. 7.6 Spectrophotometry Using a suitable pipette(6.6), transfer a volume (V) of the distillate obtained in7.4 and containing no more than1754g of nitrogen (in general between25ml and50ml, according to the expected nitrogen content of the product) into a100ml conical flask(6.4).
