BS EN ISO 11212-4-1997 Starch and derived products - Heavy metals content - Determination of cadmium content by atomic absorption spectrometry with electrothermal atomization《淀粉和淀粉.pdf

1、BRITISH STANDARD BS EN ISO 11212-4:1997 Incorporating Amendment No.1 Starch and derived products Heavy metals content Part 4: Determination of cadmium content by atomic absorption spectrometry with electrothermal atomization The European Standard EN ISO11212-4:1997 has the status of a British Standa

2、rd ICS 67.180.20BSENISO11212-4:1997 This British Standard, having been prepared under the directionof the Consumer Products and Services Sector Board, was published under theauthority of the StandardsBoard and comesintoeffect on 15 May1997 BSI 06-1999 ISBN 0 580 27459 4 National foreword This Britis

3、h Standard is the English language version of EN ISO11212-4:1997. It is identical with ISO11212-4:1997 and Technical Corrigendum1:1997 and implements it as the UK national standard. This British Standard has been produced to fulfil BSIs obligation to implement all European Standards but, because of

4、the absence of interest in the UK in the subject concerned, there has been no UK participation in the preparation of ENISO11212-4. Any queries relating to the EN should be directed to BSI, quoting the reference AW/100. Cross-references The British Standards which implement international or European

5、publications referred to in this document may be found in the BSI Standards catalogue under the section entitled “International Standards Correspondence Index”, or using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary pr

6、ovisions 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 cover, pages i and ii, theEN ISO tit

7、le page, page 2, the ISO title page, page ii, pages1 to4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication

8、Amd. No. Date Comments 9841 January 1998 Indicated by a sideline in the marginBSENISO11212-4:1997 BSI 06-1999 i Contents Page National foreword Inside front cover Foreword 2 Foreword ii Text of ISO11212-4 1ii blankEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 11212-4 March 1997 ICS 67.180

9、 Incorporates corrigendum September1997 Descriptors: See ISO document English version Starch and derived products Heavy metals content Part4: Determination of cadmium content by atomic absorption spectrometry with electrothermal atomization (ISO11212-4:1997) Amidons, fcules et produits drivs Teneur

10、en mtaux lourds Partie4: Dtermination de la teneur en cadmium par spectromtrie dabsorption atomique avec atomisation lectrothermique (ISO11212-4:1997) Strke und Strkederivate Schwermetallgehalt Bestimmung des Cadmiumgehaltes durch Atomabsorptionsspektrometrie mit elektrothermischer Atomisierung (ISO

11、/DIS11212-4:1997) This European Standard was approved by CEN on1997-02-28. 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 standard without any alteration. Up-to-date lists and bibliog

12、raphical 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 language made by translation under the responsibility of a

13、 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, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Sp

14、ain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr 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 n

15、ational Members Ref. No. EN ISO11212-4:1997 EENISO11212-4:1997 BSI 06-1999 2 Foreword The text of the International Standard ISO11212-4:1997 has been prepared by Technical Committee ISO/TC93, Starch (including derivatives and by-products, in collaboration with CEN/CS. This European Standard shall be

16、 given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by September1997, and conflicting national standards shall be withdrawn at the latest by September1997. According to CEN/CENELEC Internal Regulations, the national standards organiza

17、tions of 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 and the United Kingdom. Endorsement notice The text of the Inter

18、national Standard ISO11212-4:1997 was approved by CEN as a European Standard without any modification. Contents Page Foreword 2 1 Scope 1 2 Definition 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Procedure 3 7 Expression of results 3 8 Precision 3 9 Test report 4 Annex A (informative) Results of int

19、erlaboratory test Inside back cover Figure 1 Digestion apparatus 2 Table A.1 Interlaboratory test on corn starch Inside back coverENISO11212-4:1997 ii BSI 06-1999 Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodi

20、es). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and

21、non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodi

22、es for voting. Publication as an International Standard requires approval by at least75% of the member bodies casting a vote. International Standard ISO11212-4 was prepared by Technical Committee ISO/TC93, Starch (including derivatives and by-products). ISO11212 consists of the following parts, unde

23、r the general title Starch and derived products Heavy metals content. Part 1: Determination of arsenic content by atomic absorption spectrometry; Part 2: Determination of mercury content by atomic absorption spectrometry; Part 3: Determination of lead content by atomic absorption spectrometry with e

24、lectrothermal atomization; Part 4: Determination of cadmium content by atomic absorption spectrometry with electrothermal atomization. Annex A of this part of ISO11212 is for information only. Descriptors: Starches, food starch, chemical analysis, determination of content, heavy metals, cadmium, ato

25、mic absorption spectrometric method.ENISO11212-4:1997 BSI 06-1999 1 1 Scope This part of ISO11212 specifies a method for the determination of the cadmium content of starch, including derivatives and by-products, by atomic absorption spectrometry with electrothermal atomization. The number of paramet

26、ers for the procedure involved in the electrothermal atomization is far larger than in flame atomization; it is thus impossible to propose a comprehensive method likely to ensure the attainment of satisfactory results on all types of apparatus currently available. Each analyst should therefore optim

27、ize the conditions of use of his/her own apparatus on the basis of general or particular instructions. 2 Definition For the purposes of this part of ISO11212, the following definition applies. 2.1 cadmium content quantity of cadmium determined in accordance with the conditions specified in this meth

28、od and expressed as cadmium (Cd), in micrograms per kilogram of the product as received 3 Principle Wet digestion of the organic matrix. Injection of an aliquot portion of digested sample, in the presence of a matrix modifier, into the furnace of an electrothermal atomization atomic absorption spect

29、rometer. Measurement of the absorbance at a wavelength of228,8nm. Determination of the concentration of cadmium in the sample by means of a calibration curve. 4 Reagents Use only reagents of recognized analytical grade and distilled water or water of equivalent purity. 4.1 Nitric acid ( 20= 1,38g/ml

30、). 4.2 Hydrogen peroxide, 30% (V/V) solution. 4.3 Matrix modifier, consisting of a1g/l solution of palladium nitrate. 4.4 Cadmium standard solution,1 g/l. Standard solutions are commercially available at this concentration. These solutions may also be prepared by weighing and dissolving the salt or

31、metal of known purity. 4.5 Calibration solutions Before each series of measurements, prepare from the standard cadmium solution(4.4) at least five calibration solutions covering the range of concentrations to be determined. 100ml of each calibration solution shall contain7,5ml of nitric acid(4.1) an

32、d20ml of the matrix modifier solution(4.3) if the latter is not distributed by the automatic injection device. 5 Apparatus All the glassware used shall be previously washed by means of suitable products (such as nitric acid) and rinsed with distilled water to eliminate any trace of cadmium. Use ordi

33、nary laboratory apparatus and, in particular, the following. 5.1 Digestion apparatus (see Figure 1), made of borosilicate glass and consisting of three elements terminating with conical ground joints(5.1.1 to5.1.3). 5.1.1 Soxhlet extraction tube, of capacity200ml, equipped with a stopcock and a late

34、ral tube connected directly to the flask(5.1.3). 5.1.2 Cooling apparatus, 35 cm long, connected to the top, of the Soxhlet extraction tube(5.1.1). 5.1.3 Round-bottom flask, of capacity250ml, connected to the lower part of the Soxhlet extraction tube(5.1.1). When the stopcock is open, the device is u

35、nder reflux; when it is closed, the Soxhlet extraction tube(5.1.1) retains the condensed water and acid vapours. 5.2 Atomic absorption spectrometer, consisting of five elements(5.2.1 to5.2.5). 5.2.1 High-resolution monochromator, allowing a0,2nm bandwidth slit. 5.2.2 Correcting device for non-specif

36、ic absorption. 5.2.3 Measuring and photoelectric reception device, with a response time not exceeding about10ms. 5.2.4 Detector and signal processing system, allowing recording of the maximum and/or integrated absorbance signal. 5.2.5 Cadmium discharge lamp or cadmium hollow cathode lamp.ENISO11212-

37、4:1997 2 BSI 06-1999 5.3 Electrothermic atomizer The most widely used atomizer, for which the general conditions of use are suggested, is a graphite tubular furnace placed in the optical axis of the spectrometer, heated by the Joule effect. The furnace shall be maintained in an inert atmosphere to a

38、void its destruction by oxidation when heated at a high temperature, and shall be equipped with an automatic injection device which is necessary to obtain good repeatability and to reduce the risk of contamination. 5.4 Pyrocoated graphite tube, with Lvov platform. 5.5 Pipettes and micropipettes, of

39、suitable capacity. 5.6 Analytical balance. Figure 1 Digestion apparatusENISO11212-4:1997 BSI 06-1999 3 6 Procedure 6.1 Preparation of test sample Thoroughly homogenize the sample. 6.2 Digestion Use the digestion apparatus described in5.1. Weigh, to the nearest1mg, about5g of the test sample into the

40、 flask(5.1.3). Add27,5ml of nitric acid(4.1) and1ml of hydrogen peroxide(4.2). Distil under reflux for4h leaving the stopcock open. Turn the stopcock off, continue heating and distil until about20ml 1ml of liquid are recovered in the extraction tube(5.1.1). Stop heating and allow the flask to cool.

41、Separate the flask from the extraction tube. Add20ml of water to the digested residue in the flask, bring to the boil for a few minutes, stop heating and allow to cool. Transfer the solution to a100ml volumetric flask, add20ml of the matrix modifier(4.3) (if not distributed by the automatic injectio

42、n device), dilute to the mark with distilled water and stir. 6.3 Blank test Perform digestion under the same conditions as in6.2, replacing the test portion by5ml of water. 6.4 Electrothermal atomization programme The heating programme of the furnace mainly depends on the chemical properties of the

43、substance to be analysed, on the matrix and on the method for approaching the isothermal conditions chosen. It is composed of four stages(6.4.1 to6.4.4) which shall be optimized by each laboratory. 6.4.1 Drying It is advisable to increase the temperature slowly up to a final temperature slightly hig

44、her than the boiling temperature of the solvent and to maintain this for at least5s. 6.4.2 Thermal pretreatment The temperature for this stage, during which the organic matrix is eliminated and the mineral matrix is modified, shall be adapted by adding a matrix modifier (palladium nitrate)(4.3) capa

45、ble of stabilizing the substance by heat. 6.4.3 Atomization This stage is generally performed with a quick increase in temperature together with no or a reduced flow of gas to ensure a maximum concentration of atoms in the optical path length. 6.4.4 Cleaning of the furnace Memory effects are possibl

46、e, therefore the furnace(5.3) shall be cleaned after each injection. Cleaning is generally performed for a few seconds at maximum temperature and gas flow rate. 6.5 Determination of the calibration curve Inject to the programmed furnace(5.3), 104l of the calibration solutions (4.5) and24l of the mat

47、rix modifier(4.3) if the latter is not distributed by the automatic injection device. Measure the absorbance of each calibration solution at a wavelength of228,8nm using the spectrometer(5.2). Draw the calibration curve by plotting the cadmium concentrations of the calibration solutions, expressed i

48、n micrograms per litre, as the abscissa against the corresponding values of the signal, read either in maximum absorbance or in integrated absorbance, as the ordinate. The calibration curve shall be periodically checked depending on the length of the series of analyses. 6.6 Determination Measure the

49、 absorbance of the test samples under the same conditions as the calibration solutions and compare the results with the previously plotted calibration curve. 7 Expression of results With reference to the calibration curve, determine the concentrations corresponding to the signals of the test portion and the blank. The cadmium concentration of the sample, w, expressed in micrograms per kilogram of the product as received, is given by the equation: where NOTEWhen strictly following this method, the quantification limit can rea