BS EN 12014-7-1998 Foodstuffs - Determination of nitrate and or nitrite content - Continuous flow method for the determination of nitrate content of vegetables and vegetable produc.pdf

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1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS EN 12014-7:1998 The Eu

2、ropean Standard EN 12014-7:1998 has the status of a British Standard ICS 67.080.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Foodstuffs Determination of nitrate and/or nitrite content Part 7: Continuous flow method for the determination of nitrate content of vegetables a

3、nd vegetable products after cadmium reductionBS EN 12014-7:1998 This British Standard, having been prepared under the direction of the Consumer Products and Services Sector Committee, was published under the authority of the Standards Committee and comes into effect on 15 December 1998 BSI 1998 ISBN

4、 0 580 30044 7 Amendments issued since publication Amd. No. Date Text affected National foreword This British Standard is the English language version of EN 12014-7:1998. The UK participation in its preparation was entrusted to Technical Committee AW/-/3, Food analysis Horizontal methods, which has

5、the responsibility to: aid enquirers to understand the text; present to the responsible European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list o

6、f organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International

7、Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. 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 S

8、tandard 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 10 an inside back cover and a back cover.CEN European Committee for Standardization Comite Europe en de Normalisation Europa

9、 isches Komitee fu r Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1998 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members Ref. No. EN 12014-7:1998 E EUROPEAN STANDARD EN 12014-7 NORME EUROPE ENNE EUROPA ISCHE NORM June 1998 ICS

10、 67.080.20 Descriptors: food products, vegetables, analysis methods, chemical analysis, determination of content, nitrates, nitrites English version Foodstuffs Determination of nitrate and/or nitrite content Part 7: Continuous flow method for the determination of nitrate content of vegetables and ve

11、getable products after cadmium reduction Produits alimentaires De termination de la teneur en nitrates et/ou en nitrites Part 7: De termination de la teneur en nitrates par flux continu dans les le gumes et les produits a base de le gumes, apre s re duction au cadmium Lebensmittel Bestimmung des Nit

12、rat- und/oder Nitritgehaltes Teil 7: Kontinuierliches Durchfluverfahren zur Bestimmung des Nitratgehaltes in Gemu se und Gemu seerzeugnissen nach Cadmiumreduktion This European Standard was approved by CEN on 13 May 1998. CEN members are bound to comply with the CEN/CENELEC Internal Regulations whic

13、h 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 Secretariat or to any CEN member. This European Stan

14、dard 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 official versions. CEN members are the national stan

15、dards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.Page 2 EN 12014-7:1998 BSI 1998 Foreword This European Standard has been prepared by Technica

16、l Committee CEN/TC 275, Food analysis Horizontal methods, the Secretariat of which is held by DIN. 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 December 1998, and conflicting national standards

17、 shall be withdrawn at the latest by December 1998. This series, Foodstuffs Determination of nitrates and/or nitrate content, consists of the following parts: Part 1: General considerations; Part 2: HPLC/IC method for the determination of nitrate content of vegetables and vegetable products; Part 3:

18、 Spectrometric determination of nitrate and nitrite content of meat products after enzymatic reduction of nitrate to nitrite; Part 4: Ion-exchange chromatographic (IC) method for the determination of nitrate and nitrite content of meat products; Part 5: Enzymatic determination of nitrate content of

19、vegetable-containing food for babies and infants; Part 7: Continuous flow method for the determination of nitrate content of vegetables and vegetable products after cadmium reduction. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries a

20、re bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Contents Page Foreword 2 1 Scope 3 2 Normative References

21、3 3 Principle 3 4 Reagents 3 5 Apparatus and equipment 4 6 Procedure 4 7 Calculation 6 8 Precision 6 9 Test Report 6 Annex A (informative) Preparation of activated cadmium columns 7 Annex B (informative) Figure 8 Annex C (informative) Precision data 9 Annex D (informative) Bibliography 10 Annex E (i

22、nformative) Nitrite analysis 10Page 3 EN 12014-7:1998 BSI 1998 1) c is the substance concentration. 2) w is the mass fraction. 3) Polyethyleneglycol-mono p-(1,1,3,3-tetramethylbutyl)-phenyl-ether is commercially available as Triton X 100 (pro analyse). This information is given for the convenience o

23、f users of this European Standard and does not constitute an endorsement by CEN of this product. 4) r is the mass concentration. 1 Scope This European Standard specifies a continuous flow method (CF-method) for the determination of nitrate content of vegetables and vegetable products having a nitrat

24、e content of 900 mg/kg to 5 200 mg/kg (calculated as nitrate ion). NOTE Experiences have shown that the method may also be applied for vegetables and vegetable products having a nitrate content of greater than 50 mg/kg (calculated as nitrate ion). 2 Normative references This European Standard incorp

25、orates by dated or undated 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 Europ

26、ean Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN 12014-1, Foodstuffs Determination of nitrate and/or nitrite content Part 1: General considerations. EN ISO 3696, Water for analytical laboratory us

27、e Specification and test methods. (ISO 3693:1987) 3 Principle Test portions are extracted with water and filtered. The filtrate is transferred to the dializer of the continuous flow (CF) system 1. An aliquot portion of the nitrate ions diffuses in the dializing unit with a hydrophilic membrane into

28、a slightly alkaline buffer solution in which the nitrates are reduced to nitrite by metallic cadmium. The nitrite ions react with sulfanilamide and N-1-naphthylethylenediamine to give a reddish-purple azo dye. The absorbance of this dye is determined spectrometrically at a wavelength between 520 nm

29、and 540 nm, preferably at its maximum. NOTE The CF method is an automated version of the manual procedure for nitrate determinations in leafy vegetables as prescribed by the Official Dutch Food Act 2. With the automated method the cadmium reductor may be used for a longer period of time without any

30、appreciable loss of its reducing capacity. Also ready-made cadmium columns from commercial suppliers are available, minimizing the main objection of working with this toxic element. 4 Reagents All reagents and materials used shall be of recognized analytical grade and water shall be of at least grad

31、e 1 according to EN ISO 3696. Consult safety data sheets or labels for additional information on toxicity, flammability and explosivity of chemicals used. When preparing solutions, the purities of the reagents available shall be taken into account. 4.1 Cadmium column, activated, ready-to-use, as com

32、mercially available. CAUTION Cadmium is extremely toxic for humans and the environment; take effective precautions before handling and disposing this compound. Cadmium columns may also be prepared in the laboratory according to the description given in the annex A. 4.2 Hydrochloric acid, concentrate

33、d, r 20 (HCl) = 1,18 g/l. 4.3 Hydrochloric acid, c(HCl) = 4 mol/l 1) , dilute 320 ml of hydrochloric acid (4.2) to 1 l with water. 4.4 Hydrochloric acid, c(HCl) = 0,1 mol/l. 4.5 Ammonia, w(NH 3 )=2 5% 2) . 4.6 Ammonia, w(NH 3 )=5% . 4.7 Ammonium chloride, NH 4 Cl. 4.8 Wetting agent, e.g. polyethylen

34、eglycol-mono p-(1,1,3,3-tetramethylbutyl)-phenyl-ether 3) or polyethylene glycol ether. 4.9 Wetting agent solution. Dissolve 25 g of wetting agent (4.8) into 75 ml of methanol and then add 150 ml of water. 4.10 Phosphoric acid, w(H 3 PO 4 )=8 5% . 4.11 Sulfanilamide, (NH 2 C 6 H 4 SO 2 NH 2 ). 4.12

35、N-(1-naphthyl)ethylenediamine dihydrochloride (C 10 H 7 NHCH 2 CH 2 NH 2 2 HCl). 4.13 Ethylenediamine tetracetic (EDTA) acid disodium salt dihydrate, (CH 2 N(CH 2 COOH) (CH 2 COONa) 2 2 H 2 O). 4.14 Copper sulfate solution, r(CuSO 4 5 H 2 O) = 2 g/100 ml) 4) .Page 4 EN 12014-7:1998 BSI 1998 4.15 Ext

36、racting buffer, pH 9,6 to 9,7. Add 50 ml of hydrochloric acid (4.2)t o approximately 600 ml water and mix. Add 75 ml of ammonia (4.5), dilute to 1 l with water and mix. Adjust to a pH of 9,6 to 9,7 with either hydrochloric acid (4.3 or 4.4) or ammonia (4.5 or 4.6). 4.16 Buffer solution continuous fl

37、ow. Dissolve 25 g of ammonium chloride (4.7)i n1lo f water. Add about 5 ml of wetting agent solution (4.9) and adjust to a pH of 9,0 with ammonia (4.5 or 4.6). 4.17 Diluting solution continuous flow. Add about 5 ml of 10 % wetting agent solution (4.9) to 1 l of water. 4.18 Colour reagent continuous

38、flow. Add 50 ml of phosphoric acid (4.10) and 5 g of sulfanilamide (4.11) to 250 ml of water. Dissolve completely and heat if necessary. Add 0,25 g of N-(1-naphthyl)ethylenediamine dihydrochloride (4.12) and dilute to 500 ml with water. Store at 48Ci na well-stoppered bottle in the dark. This soluti

39、on may be kept for up to 2 weeks but it should preferably be prepared daily. 4.19 Nitrate stock solution, r(NO ) = 2 g/l. 3 2 Dissolve 0,815 g of dry potassium nitrate in water and dilute with water to 250 ml in a volumetric flask. Mix well. This stock solution is stable for at least 2 months if sto

40、red at 48C. 4.20Nitratestandardsolutions,r(NO ) = 50 mg/l, 3 2 100 mg/l, 200 mg/l, 300 mg/l, 400 mg/l, 500 mg/l and 600 mg/l. Pipette 2,5 ml, 5 ml, 10 ml, 15 ml, 20 ml,25 ml and 30 ml of the nitrate stock solution (4.19) in seven subsequent 100 ml volumetric flasks. Dilute to the mark with water. Mi

41、x well. Prepare these standard solutions on the day of use. 4.21 Nitrite stock solution, r(NO ) 1 g/l. 2 2 Sodium nitrite is a hygroscopic substance. Dissolve 0,150 g of dry sodium nitrite in water and dilute to 100 ml in a volumetric flask. Mix well. This stock solution is stable for at least 2 wee

42、ks if stored at 48C. 4.22 Reducing capacity control solutions, r(NO ) 2 2 = 100 mg/l, 200 mg/l and 300 mg/l. Pipette 5 ml, 10 ml and 15 ml of the nitrite stock solution (4.21) in three subsequent 50 ml volumetric flasks. Dilute to the mark with water. Mix well. Prepare these control solutions on the

43、 day of use. 4.23 Conditioner solution, r(NO ) = 10 mg/l. 3 2 Dilute 5 ml of the nitrate stock solution (4.19)t o1l with water. Mix well. Prepare on the day of use. 4.24 EDTA solution, r(EDTA) = 34 g/l. Dissolve 3,4 g of the disodium dihydrate salt of EDTA (4.13) in 100 ml of water. 4.25 Regeneratio

44、n solution. Add about 5 ml of EDTA solution (4.24) and 2 ml of HCl solution (4.4) to 100 ml of water. 4.26 Hypochlorite solution, w(HOCl) = 0,5 %. Prepare by diluting a commercially available 5 % solution. 5 Apparatus and equipment Usual laboratory apparatus and, in particular, the following. 5.1 La

45、boratory cutter. 5.2 Balance or gravimetric dilutor. 5.3 Homogenizer. 5.4 Continuous flow system, consisting of sampler, tubing pump, nitrate CF manifold with dialyzer, cadmium reductor, colorimeter with flowcell, filter with a wavelength of between 520 nm and 540 nm and evaluation unit (see Figure

46、B.1). 6 Procedure 6.1 Sample preparation Store samples at a temperature of at least218 C. Homogenize frozen vegetable samples in a cutter (5.1). Keep homogenized samples and vegetable juices at a temperature of at least218 C until just before extraction. NOTE Storage at2188C before homogenization is

47、 required to assure cell-breakage and complete extraction. A ruggedness study showed that extraction at room temperature is then sufficient. 6.2 Sample extraction Weigh 40,0 g of frozen and homogenized sample into a 600 ml beaker. By means of a balance or gravimetric diluter (5.2), add 35,0 g of ext

48、raction buffer (4.15)t o prevent conversion of nitrate into nitrite (see note), and 325,0 g of water. Homogenize (5.3) for at least 1 min, and filter sample through fluted filter paper. Analyse the extract after filtration on the same day. Proceed as described in 6.6. NOTE Addition of extraction buf

49、fer is only needed in case nitrite is to be determined as well. If not, extraction can be performed with 360 g of water. If extraction buffer is added extracts may be kept up to 48 h at 4 C. 6.3 Insertion of cadmium column If necessary, before insertion, fill the column with water or buffer solution (4.16), e.g. by using a syringe. Sleeve both ends with transmission tubing. Start pumping buffer solution (4.16) in the CFA-system. When all tubes are filled with reagents and all air is removed f