1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS EN 1988-1:1998 The Eur
2、opean Standard EN 1988-1:1998 has the status of a British Standard ICS 67.040 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Foodstuffs Determination of sulfite Part 1: Optimized Monier-Williams methodThis British Standard, having been prepared under the direction of the Cons
3、umer Products and Services Sector Board, was published under the authority of the Standards Board and comes into effect on 15 June 1998 BSI 1998 ISBN 0 580 29239 8 BS EN 1988-1:1998 Amendments issued since publication Amd. No. Date Text affected National foreword This British Standard is the English
4、 language version of EN 1988-1:1998. The UK participation in its preparation was entrusted to Technical Panel AW/-/3, Food analysis Horizontal methods, which has the responsibility to: aid enquirers to understand the text; present to the responsible European committee any enquiries on the interpreta
5、tion, 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 panel can be obtained on request to its secretary. Cross-references The British Standards which implem
6、ent 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. A British Standard does not purpor
7、t to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cov
8、er, the EN title page, pages 2 to 7 and a back cover.CEN European Committee for Standardization Comite Europe en de Normalisation Europa 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 worl
9、dwide for CEN national Members. Ref. No. EN 1988-1:1998 E EUROPEAN STANDARD EN 1988-1 NORME EUROPE ENNE EUROPA ISCHE NORM February 1998 ICS 67.040 Descriptors: Food products, chemical analysis, determination of content, sulfites, procedures English version Foodstuffs Determination of sulfite Part 1:
10、 Optimized Monier-Williams method Produits alimentaires Dosage des sulfites Partie 1: Me thode optimise e de Monier-Williams Lebensmittel Bestimmung von Sulfit Teil 1: Optimiertes Monier-Williams-Verfahren This European Standard was approved by CEN on 1 January 1998. CEN members are bound to comply
11、with the CEN/CENELEC Internal Regulations which 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 Secret
12、ariat or to any CEN member. This European Standard 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 offici
13、al versions. CEN members are the national standards 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 1988-1:1998 BSI 1998 Foreword This Eu
14、ropean Standard has been prepared by Technical 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 Augu
15、st 1998, and conflicting national standards shall be withdrawn at the latest by August 1998. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Fi
16、nland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. This European Standard: Foodstuffs Determination of sulfite consists of the following parts: Part 1: Optimized Monier-Williams method; Part 2: Enzyma
17、tic method. Contents Page Foreword 2 Introduction 3 1 Scope 3 2 Normative references 3 3 Principle 3 4 Reagents 3 5 Apparatus 4 6 Procedure 5 7 Precision 6 8 Test report 6 Annex A (informative) Bibliography 7 Annex B (informative) Precision data 7Page 3 EN 1988-1:1998 BSI 1998 1) It has been shown t
18、hat the analysis of isolated soy protein leads to false positive results in the range of 20 mg/kg to 30 mg/kg expressed as sulfur dioxide. Therefore, when analysing foodstuffs containing isolated soy proteins a proportional enhancement of the result may be obtained and is taken into account. Introdu
19、ction Sulfite can be used as a preservative of foodstuffs. In order to minimize possible negative health effects, many countries have regulated the use of sulfite in foods. This has resulted in the development of several methods of analysis to detect the presence and quantity of sulfite in a great v
20、ariety of foods. 1 Scope This European Standard specifies a distillation method for the determination of the sulfite content, expressed as sulfur dioxide, in foodstuffs, in which the content of sulfite is at least 10 mg/kg. The method is applicable in the presence of other volatile sulfur compounds.
21、 It is not applicable to cabbage, dried garlic, dried onions, ginger, leeks and soy proteins 1) . It has been shown that the analysis of isolated soy protein leads to false positive results. Specific products, for which European Standards for the determination of the sulfites exist, are excluded fro
22、m the scope of this horizontal European Standard. 2 Normative references This part of this European Standard incorporates 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 here
23、after. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN ISO 3696, Water for analytical l
24、aboratory use Specification and test methods (ISO 3696:1987). 3 Principle Free sulfite plus reproducible portion of bound sulfites (such as carbonyl addition products) in foods are measured. The test portion is heated with a refluxing solution of hydrochloric acid to convert sulfite to sulfur dioxid
25、e. A stream of nitrogen is introduced below the surface of the refluxing solution to sweep sulfur dioxide through a water-cooled condenser and, via a bubbler attached to the condenser, into the hydrogen peroxide solution, where sulfur dioxide is oxidized to sulfuric acid. The generated sulfuric acid
26、 is titrated with standardized sodium hydroxide solution. The sulfite content is directly related to the generated sulfuric acid. See 1, 2. 4 Reagents During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only water of at least grade 3 as defined in EN IS
27、O 3696. 4.1 Hydrochloric acid, substance concentration c(HCl) = 4 mol/l. For each analysis, prepare 90 ml of solution by adding (carefully) 30 ml of concentrated hydrochloric acid (36 %) to 60 ml of water and mix. Prepare a fresh solution daily. 4.2 Sodium hydroxide standard solution, c(NaOH) = 0,01
28、0 mol/l. 4.3 Methyl red indicator. Dissolve 250 mg of methyl red in 100 ml of ethanol. 4.4 Hydrogen peroxide solution, volume fraction f (H 2 O 2 )=3% . Just prior to use, add 3 drops of methyl red indicator and titrate with sodium hydroxide standard solution (4.2) to yellow end point. If end point
29、is exceeded, discard the solution. 4.5 Ethanol or methylated spirit. 4.6 Ethanolwater mixture, volume fraction f of ethanol = 5 %. 4.7 Nitrogen. High purity, used with regulator to maintain flow of 200 ml/min. To guard against oxygen in nitrogen gas, use an absorber as used in the gas chromatographi
30、c analysis. Alternatively, an oxygen-scrubbing solution, such as alkaline 1,2,3 trihydroxibenzene (pyrogallol), in a gas-washing bottle may be used. Prepare the gas-washing bottle as follows. Add 4,5 g of 1,2,3 trihydroxibenzene to the gas-washing bottle. Purge the gas-washing bottle with nitrogen f
31、or 2 min to 3 min. Prepare a potassium hydroxide solution by adding 65 g of potassium hydroxide to 85 ml of water. (Caution: heat is generated). Add the potassium hydroxide solution to the gas-washing bottle while an atmosphere of nitrogen is maintained in the gas-washing bottle.Page 4 EN 1988-1:199
32、8 BSI 1998 2) This description of a distillation apparatus refers to 1 in annex A and is given as information for the convenience of users of this European Standard. This information does not constitute an endorsement by CEN of the glassware named. Equivalent glassware (such as the distillation appa
33、ratus described in ISO 5522:1981, see 3 in annex A of this standard) may be used if it can be shown to lead to the same results. 5 Apparatus 5.1 Distillation apparatus. Assemble the apparatus 2) (see Figure 1), which includes the following. Inlet adapter (1) with hose connector and rubber bulb to ap
34、ply a head pressure above the solution. The use of a pressure equalizing dropping funnel is not recommended because the condensate, possibly containing sulfur dioxide, is deposited in the funnel and side arm. Cylindrical dropping funnel (2) of$ 100 ml capacity. Round-bottomed flask (3) of capacity 1
35、 l, with three suitable leakproof joints. Gas inlet tube (4) of sufficient length to permit the introduction of nitrogen within 25 mm of the bottom of the flask. 1 Inlet adapter 2 Cylindrical dropping funnel 3 Round-bottomed flask 4 Gas inlet tube 5 Bulb condenser 6 Bubbler 7 Vessel Figure 1 Distill
36、ation apparatus for optimized Monier-Williams method Bulb condenser (5), jacket length 300 mm. Bubbler (6), fabricated from glass according to dimensions in Figure 2. Vessel (7), of approximately 25 mm inner diameter and 180 mm length. NOTE If back pressure is kept as low as possible, losses of sulf
37、ur dioxide through leaks can be avoided. A thin film of stopcock grease on sealing surfaces of all joints except the joint between the cylindrical dropping funnel and the flask is helpful. Joints which are clamped together help to ensure a complete seal throughout the analysis. 5.2 Burette, of capac
38、ity 10 ml with overflow tube and hose connections for sodium hydroxide adsorbed on silicon dioxide, or an equivalent air-scrubbing apparatus to permit the maintenance of a carbon dioxide-free atmosphere over the sodium hydroxide standard solution (4.2). 5.3 Condenser coolant. Chill condenser with co
39、olant, such as a circulating mixture of 1 part (volume fraction) of methanol and 2 parts of water, or continuous water flow, maintained at not more than 158C. 5.4 Heating mantle, capable of being controlled between 208C and 1208C. 5.5 Food processor or blender. 5.6 Oxygen absorber, to guard against
40、oxygen in nitrogen gas (4.7). Dimensions in millimetres Figure 2 Enlarged diagram of bubbler for the distillation apparatusPage 5 EN 1988-1:1998 BSI 1998 6 Procedure 6.1 General Carry out sample preparation and analysis as quickly as possible to avoid loss of labile forms of sulfite. NOTE To become
41、familiar and proficient with the method before routine use, it is recommended that food test portions containing known amounts of sulfite are analysed. The analysis should be performed in a manner that precludes any loss of sulfite by oxidation or reaction with components in food. Since sulfites are
42、 reactive with air and food matrices and often lack stability, portions are fortified with a stable source of sulfite, not sodium sulfite or similar salts. Sodium hydroxymethylsulfonate (HMS), which is a bisulfite addition product of formaldehyde and which is structurally similar to some combined fo
43、rms of sulfite in foods, is useful for preparing stable fortified test materials. For analysis, 50 g of prepared sample of sulfite-free food are transferred to the flask (Figure 1; item 3). An aliquot portion of aqueous solution of HMS sodium salt is added. The solution is analysed immediately. HMS
44、recoveries of more than 80 % from food matrices fortified at 10 mg/kg are recommended to ensure accurate analytical data. 6.2 Sample preparation 6.2.1 Solid samples Transfer 50 g of food, or a quantity that contains 500mg to 1500mg of sulfur dioxide, to a food processor or blender. Add 100 ml of the
45、 ethanol/water mixture (4.6) and briefly grind the mixture. Continue the grinding or blending only until the food is chopped into pieces small enough to pass through the ground glass joint of the flask (Figure 1; item 3). 6.2.2 Liquid samples Mix 50 g of test sample, or quantity that contains 500mg
46、to 1500mg of sulfur dioxide, with 100 ml of the ethanol/water mixture (4.6). 6.3 System preparation Use the distillation apparatus (5.1) assembled as shown in Figure 1, put the flask (Figure 1; item 3) in the heating mantle (5.4) and add 400 ml of water to the flask. Close the stopcock of the funnel
47、 (Figure 1; item 2) and add 90 ml of hydrochloric acid solution (4.1) to the funnel. Begin nitrogen flow at 200 ml/min 10 ml/min and initiate the condenser coolant (5.3) flow. Add 30 ml of 3 % hydrogen peroxide solution (4.4) to the vessel (Figure 1; item 7). After 15 min, the apparatus and water wi
48、ll be thoroughly deoxygenated and the prepared test portion may be introduced into the apparatus. 6.4 Sample introduction and distillation Remove the dropping funnel (Figure 1; item 2) and quantitatively transfer the test portion in aqueous ethanol to the flask (Figure 1; item 3). Wipe the tapered j
49、oint clean with a laboratory tissue, quickly apply stopcock grease to the outer joint of the funnel, and return the funnel to the flask. Examine each joint to be sure that it is sealed. Use a rubber bulb equipped with a valve to apply head pressure above the hydrochloric acid solution in the funnel. Open the stopcock of the funnel and let hydrochloric acid solution flow into the flask. Continue to maintain sufficient pressure above the hydrochloric acid solution to force the solution into the flask. The stopco
