1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS EN 12135 : 1998 The Eu
2、ropean Standard EN 12135 : 1997 has the status of a British Standard ICS 67.160.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Fruit and vegetable juices Determination of nitrogen content Kjeldahl methodThis British Standard, having been prepared under the direction of the
3、 Consumer Products and Services Sector Board, was published under the authority of the Standards Board and comes into effect on 15 February 1998 BSI 1998 ISBN 0 580 28965 6 BS EN 12135 : 1998 Amendments issued since publication Amd. No. Date Text affected National foreword This British Standard is t
4、he English language version of EN 12135 : 1997. The UK participation in its preparation was entrusted to Technical Committee AW/21, Fruit and vegetable juices, which has the responsibility to: aid enquirers to understand the text; present to the responsible European committee any enquiries on the in
5、terpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards
6、which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled International Standards Correspondence Index, or by using the Find facility of the BSI Standards Electronic Catalogue. Compliance with a British
7、Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, the EN title page, pages 2 to 6, an inside back cover and a back cover.CEN European Committee for Standardization Comite Europe en de Normalisation Europ
8、a isches Komitee fu r Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1997 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 12135 : 1997 E EUROPEAN STANDARD EN 12135 NORME EUROPE ENNE EUROPA ISCHE NORM September 199
9、7 ICS 67.160.20 Descriptors: Fruit and vegetable juices, chemical analysis, determination of content, nitrogen, Kjeldahl method English version Fruit and vegetable juices Determination of nitrogen content Kjeldahl method Jus de fruits et de le gumes Dosage de lazote Me thode de Kjeldahl Frucht- und
10、Gemu sesa fte Bestimmung des Stickstoffgehaltes Kjeldahlverfahren This European Standard was approved by CEN on 6 September 1997. 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 national standa
11、rd 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 any other lan
12、guage 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, Czech Republic, Denmark, Finland, France, Germany, Greece,
13、 Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.Page 2 EN 12135 : 1997 BSI 1998 Foreword This European Standard has been prepared by Technical Committee CEN/TC 174, Fruit and vegetable juices Methods of analysis, the secretariat of w
14、hich is held by AFNOR. 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 March 1998, and conflicting national standards shall be withdrawn at the latest by March 1998. According to the CEN/CENELEC I
15、nternal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerl
16、and and the United Kingdom. Contents Page Foreword 2 1 Scope 3 2 Normative references 3 3 Definition and symbols 3 4 Principle 3 5 Reagents 3 6 Apparatus 4 7 Procedure 4 8 Calculation 4 9 Precision 5 10 Test report 5 Annexes A (informative) Bibliography 6 B (informative) Statistical results of the i
17、nter-laboratory test 6Page 3 EN 12135 : 1997 BSI 1998 1 Scope This European Standard specifies a method for the determination of the nitrogen content of fruit and vegetable juices and related products by the Kjeldahl method. 2 Normative references This European Standard incorporates by dated or unda
18、ted reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when
19、incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN 1131 : 1994 Fruit and vegetable juices Determination of the relative density EN ISO 3696 : 1995 Water for analytical laboratory use Specification and test methods (ISO 36
20、96 : 1987) ISO 5725 : 1986 Precision of test methods Determination of repeatability and reproducibility for a standard test method by inter-laboratory tests 3 Definition and symbols 3.1 Definition For the purposes of this European Standard the following definition applies: 3.1.1 total nitrogen conte
21、nt The quantity of nitrogen present in the product and corresponding to the ammonia produced and determined under the conditions specified in this European Standard, expressed in milligrams per litre or milligrams per kilogram. 3.2 Symbols For the purposes of this European Standard the following sym
22、bols apply: c substance concentration; r mass concentration; f volume fraction. 4 Principle Digestion of a test portion with concentrated sulfuric acid, using a catalyst, to convert organic nitrogen into ammonium sulfate; adjustment of the diluted solution to alkaline pH, distillation of the liberat
23、ed ammonia into an excess of boric acid solution, titration with sulfuric acid or hydrochloric acid to determine the ammonia bound by the boric acid, and calculation of the nitrogen content of the sample from the amount of ammonia produced. 5 Reagents Use only reagents of recognized analytical grade
24、 and only water in accordance with at least grade 3 of EN ISO 3696 : 1995. 5.1 Sulfuric acid, r 20 (H 2 SO 4 ) = 1,84 g/ml. WARNING. Concentrated sulfuric acid is corrosive and causes burns! Wear non-permeable gloves. Avoid contact with skin. 5.2 Sulfuric acid standard volumetric solution, c(H 2 SO
25、4 ) = 0,05 mol/l. 5.3 Hydrochloric acid standard volumetric solution, c(HCl) = 0,1 mol/l, alternative to 5.2. 5.4 Potassium sulfate (K 2 SO 4 ). 5.5 Copper (II) sulfate (CuSO 4 ), anhydrous. 5.6 Copper (II) sulfate pentahydrate (CuSO 4 5H 2 O), alternative to 5.5. 5.7 Catalyst mixture, 100 g of pota
26、ssium sulfate (5.4) and 10 g of copper (II) sulfate (5.5) or 15,64 g of copper (II) sulfate pentahydrate (5.6) are thoroughly mixed in a mortar (6.8). 5.8 Selenium dioxide (SeO 2 ). 5.9 Sodium hydroxide solution, dissolve 400 g of sodium hydroxide (NaOH) in water and dilute to 1 000 ml. 5.10 Boric a
27、cid solution, dissolve 20 g of boric acid (H 3 BO 3 ) in water and dilute to 1 000 ml. 5.11 Indicator solution, mixed indicator, prepared by dissolving 100 mg of methyl red and 50 mg of methylene blue in 100 ml of ethanol, f (CH 3 CH 2 OH) = 95 %.Page 4 EN 12135 : 1997 BSI 1998 1) Parnas-Wagner is a
28、n example of a suitable product available commercially. This information is given for the convenience of users of this standard and does not constitute an endorsement by CEN of this product. 6 Apparatus Usual laboratory apparatus and, in particular, the following. 6.1 Kjeldahl flask, of 100 ml capac
29、ity. 6.2 Digestion apparatus, with an effective suction device, for acid fumes evolved during the digestion. 6.3 Distillation apparatus, e.g. Parnas-Wagner type 1) . 6.4 Pipette, of 10 ml capacity. 6.5 Measuring cylinder, of 25 ml capacity. 6.6 Burette, graduated in 0,1 ml. 6.7 Conical flask. 6.8 Mo
30、rtar. 6.9 Boiling aids. 7 Procedure 7.1 Preparation of the test sample Normally products shall not be pre-treated, however dilution may be necessary and their analysis by this method shall be on a volumetric basis, results being expressed per litre of sample. The analysis of concentrated products ma
31、y also be carried out on a volumetric basis, after dilution to a known relative density. In this case, the relative density shall be indicated. Based on a weighed sample and taking the dilution factor for analysis into account, the results may also be expressed per kilogram of product. In products w
32、ith a high viscosity and/or a very high content of cells (for example pulp), a determination on the basis of a weighed test sample is the usual procedure. 7.2 Determination 7.2.1 Digestion Pipette 10 ml of test sample (V s ) into a Kjeldahl flask (6.1) and transfer to the flask a few pieces of boili
33、ng aids (6.9). Heat gently in or on the digestion apparatus (6.2) until the test sample becomes dark but do not evaporate fully to dryness. Allow to cool. Calculate the soluble solids content of the test sample from the relative density determined using EN 1131. Use 4 ml of concentrated sulfuric aci
34、d (5.1) per gram of soluble solids, most of which should be sugar. Transfer into the Kjeldahl flask (6.1) after cooling, the calculated amount of concentrated sulfuric acid (5.1) plus 1 ml excess. Add 0,9 g of catalyst mixture (5.7) and a granule of selenium dioxide (5.8). NOTE. For example, 10 ml o
35、f test sample with a relative density of 1,040 and a soluble solids content of 1 g requires 5 ml of concentrated sulfuric acid (i.e. 4 ml plus 1 ml). Heat gently again on or in the digestion apparatus (6.2), boil until the solution is clear, and rotate the flask frequently until no particles of mate
36、rial are left in the neck of the flask. Then keep the liquid boiling for another 60 min. Allow to cool to room temperature. Carefully add about 35 ml of water. Mix and cool again. 7.2.2 Distillation Transfer into a conical flask (6.7) 30 ml of the boric acid solution (5.10) and one or two drops of t
37、he indicator solution (5.11). Mix. Place the conical flask under the condenser so that the tip of the outlet tube is immersed in the boric acid solution. Transfer the contents of the Kjeldahl flask quantitatively to the distillation apparatus (6.3). Add 20 ml of the sodium hydroxide solution (5.9) b
38、y means of a measuring cylinder (6.5). Distil so that about 100 ml of distillate is collected in approximately 4 min to 5 min. Make sure that the distillate is cooled effectively and the contents of the conical flask does not exceed 258C during the distillation. About 30 s before the end of the dist
39、illation, lower the conical flask so that the tip of the outlet tube is no longer immersed in the acid solution and rinse the tip with a small amount of water. 7.2.3 Titration Titrate the distillate in the conical flask using the standard volumetric solution (5.2 or 5.3) until the indicator turns to
40、 pink. Record the volume (V)o f sulfuric or hydrochloric acid solution required. 8 Calculation Calculate the total nitrogen content r N of the test sample in milligrams per litre using the following equation: r N = 1,4 V 1 000 V s where: V is the volume in millilitres of sulfuric (5.2)o r hydrochlor
41、ic acid solution (5.3) required for the determination V s is the volume in millilitres of the test portion Take into account the dilution factor and the relation of the value to mass or volume. If a concentrated product has been diluted to single strength, report the relative density of the single s
42、trength sample. Express the nitrogen content r N of the test sample without a decimal place.Page 5 EN 12135 : 1997 BSI 1998 9 Precision Details of the inter-laboratory test on precision of the method are summarized in annex B. The values derived from the inter-laboratory test may not be applicable t
43、o analyte concentration ranges and matrices other than given in annex B. 9.1 Repeatability The absolute difference between two single test results found on identical test material by one operator using the same apparatus within the shortest feasible time interval will exceed the repeatability limit
44、r in not more than 5 % of the cases. The value is: r = 24 mg/l. 9.2 Reproducibility The absolute difference between two single test results on identical test material reported by two laboratories will exceed the reproducibility limit R in not more than 5 % of the cases. The value is: R = 86 mg/l. 10
45、 Test report The test report shall contain the following data: all information necessary for the identification of the sample (kind of sample, origin of sample, designation); a reference to this European Standard; the date and type of sampling procedure (if known); the date of receipt; the date of t
46、est; the test results and units in which they have been expressed; whether the repeatability of the method has been verified; any particular points observed in the course of the test; any operations not specified in the method or regarded as optional, which might have affected the results.Page 6 EN
47、12135 : 1997 BSI 1998 Annex A (informative) Bibliography Determination of total nitrogen: No 28, 1991 - In: The collected Analyses of the International Federation of Fruit Juice Producers Loose-leaf edition, as of 1996 - Zug: Swiss Fruit Union. Annex B (informative) Statistical results of the inter-
48、laboratory test In accordance with ISO 5725 : 1986, the following parameters have been defined in an inter-laboratory test. (For literature pertaining to the method see annex A). The test was conducted by the International Fruit Union, Paris, France. Year of inter-laboratory test 1990 number of labo
49、ratories 18 number of samples 2 Table B.1 Sample A B Number of laboratories retained after eliminating outliers 14 13 Number of outliers (laboratories) 4 3 Number of accepted results 76 68 Mean value ( x ) (mg/l) 1096 1347 Repeatability standard deviation (S r ) (mg/l) 6,91 10,37 Repeatability relative standard deviation (RSD r ) (%) 0,6 0,8 Repeatability limit (r) (mg/l) 19 29 Reproducibility standard deviation (S R ) (mg/l) 26,37 35,20 Reproducibility relative standard deviation (RSD R ) (%) 2,4 2,6 R
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