1、BRITISH STANDARD BS ISO 6561-2:2005 Fruits, vegetables and derived products Determination of cadmium content Part 2: Method using flame atomic absorption spectrometry ICS 67.080.01 BS ISO 6561-2:2005 This British Standard was published under the authority of the Standards Policy and Strategy Committ
2、ee on 24 January 2005 BSI 24 January 2005 ISBN 0 580 45352 9 National foreword This British Standard reproduces verbatim ISO 6561-2:2005 and implements it as the UK national standard. Any enquiries on this text should be forwarded to Head of International Content, Standards Development, BSI, 389 Chi
3、swick High Road, London W4 4AL who will present to the responsible international/European committee any such enquiries on the interpretation, or proposals for change, and keep UK interests informed. Cross-references The British Standards which implement international publications referred to in this
4、 document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a cont
5、ract. Users are responsible for its 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, the ISO title page, pages ii and iii, a blank page, pages 1 to 6, an i
6、nside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments Reference number ISO 6561-2:2005(E)INTERNATIONAL ADNATSDR ISO 6-1652 tide tsriFino -500210-20 Fruits, vegetab
7、les and derived products Determination of cadmium content Part 2: Method using flame atomic absorption spectrometry Fruits, lgumes et produits drivs Dtermination de la teneur en cadmium Partie 2: Mthode par spectromtrie dabsorption atomique avec flamme Referecne unbmer OSI 2-1656002:)E(5INTERNATIONA
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9、muqiva ece malfem BSISO65612:2005 ii BSISO65612:2005 iiiForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees
10、. 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 non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the Intern
11、ational Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Sta
12、ndards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subj
13、ect of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 6561-2 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 3, Fruit and vegetable products. This first edition of ISO 6561-2, together with ISO 6561-1:2004, cancels an
14、d replaces ISO 6561:1983, which has been technically revised. ISO 6561 consists of the following parts, under the general title Fruits, vegetables and derived products Determination of cadmium content: Part 1: Method using graphite furnace atomic absorption spectrometry Part 2: Method using flame at
15、omic absorption spectrometry BSISO65612:2005blankINTENRATIONAL TSANDADR IS-1656 O2:(5002E)1Fruits, vegetables and derived products Determination of cadmium content Part 2: Method using flame atomic absorption spectrometry 1 Scope This part of ISO 6561 specifies an atomic absorption spectrometric met
16、hod for the determination of the cadmium content of fruits, vegetables and derived products. NOTE The method of cadmium determination in fruit, vegetables and derived products is based on AOAC Official Methods of Analysis 1 . 2 Principle This method is based on the decomposition of organic matter wi
17、th HNO 3 , H 2 SO 4and H 2 O 2 , extraction of cadmium by dithizone-CHCl 3at pH 9, and determination of cadmium by flame atomic absorption spectrometry. 3 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and water which has been distilled twice in borosilicate g
18、lass apparatus, or water of at least equivalent purity. 3.1 Nitric acid, concentrated ( 20= 1,38 g/ml). 3.2 Sulfuric acid, concentrated ( 20= 1,84 g/ml). 3.3 Hydrochloric acid, dilute, 0,2 mol/l. Place 16,5 ml of concentrated hydrochloric acid ( 20= 1,19 g/ml) into a 1 000 ml one-mark volumetric fla
19、sk and dilute to the mark with water. Mix. 3.4 Hydrogen peroxide, concentrated (50 %). 3.5 Citric acid monohydrate. 3.6 Sodium hydroxide, 0,05 mol/l solution. 3.7 Thymol blue indicator. Triturate 0,1 g of thymol blue indicator in an agate mortar with 4,3 ml of sodium hydroxide solution (3.6). Dilute
20、 to 200 ml in a flask with water. 3.8 Ammonia solution, 28 % to 30 % solution. BSISO65612:20052 3.9 Chloroform. 3.10 Dithizone, 1,0 mg/ml solution. Place 0,2 g of dithizone in a 200 ml volumetric flask and add chloroform to the mark. 3.11 Dithizone, 0,2 mg/ml solution. Dilute dithizone solution (3.1
21、0) 1 + 4 with chloroform (3.9). Prepare fresh daily. 3.12 Cadmium standard solution, corresponding to a cadmium concentration of 1,0 mg/ml. 4 Apparatus Before use, wash all glassware with 8 mol/l nitric acid, followed by a thorough rinse with water. Cover beakers with watch glasses during all operat
22、ions. Usual laboratory apparatus and, in particular, the following. 4.1 Mechanical grinder, the inside and the blades of which are coated with polytetrafluoroethylene (PTFE). 4.2 Round-bottom flasks, of 1 500 ml capacity. 4.3 Beaker, of 400 ml capacity. 4.4 One-mark volumetric flasks, of capacities
23、50 ml, 100 ml and 1 000 ml. 4.5 Pipettes, of appropriate capacity. 4.6 Separators, 125 ml and 250 ml capacities. 4.7 Atomic absorption spectrometer, provided with an air/acetylene burner (10 cm), suitable for measurements at a wavelength of 228,8 nm. 4.8 Burner or heating mantle. 4.9 Hot plate. 4.10
24、 Analytical balance. 5 Sampling A representative sample should have been sent to the laboratory. It should not have been damaged or changed during transport or storage. Sampling is not part of the method specified in this part of ISO 6561. If there is no specific International Standard dealing with
25、the product concerned, it is recommended that the parties concerned come to an agreement on the subject. BSISO65612:2005 36 Procedure 6.1 Preparation of test sample Mix well the laboratory sample, if necessary, first remove any seeds, stalks and hard seed-cavity walls, and then grind in the mechanic
26、al grinder (4.1). Frozen or deep-frozen products shall be previously thawed in a closed vessel, and the liquid formed during this process shall be added to the product before mixing. 6.2 Test portion Weigh, to the nearest 0,01 g, 50 g of the test sample (6.1) into a 1 500 ml round-bottom flask (4.2)
27、. 6.3 Decomposition If the test portion contains ethanol, first remove the ethanol by evaporation. Add several boiling chips or beads and carefully add 25 ml of nitric acid (3.1). Cover and warm gently using a burner or heating mantle (4.8) to initiate reaction. When reaction subsides, add 25 ml of
28、nitric acid (3.1), warm again and continue until 100 ml of nitric acid (3.1) has been added. Alternatively, add carefully 100 ml of nitric acid (3.1) to the test portion at once, and allow it to stand at room temperature overnight. Heat until most NO fumes have evolved; control excessive frothing by
29、 cooling or quenching with water from a washbottle. Add 20 ml of concentrated sulfuric acid (3.2) to the solution. Dilute to approximately 300 ml with water and evaporate using a burner or heating mantle (4.8) until charring begins. When charring becomes extensive, cautiously add hydrogen peroxide (
30、3.4), 1 ml at a time. Let the reaction subside before adding the next portion of oxidant, and never add more than 1 ml at a time. Continue the addition of hydrogen peroxide until the solution is colourless. Heat vigorously to SO 3fumes, adding more hydrogen peroxide (3.4) as required, to remove char
31、. Heat vigorously to expel excess of hydrogen peroxide. Cool colourless digest to room temperature. 6.4 Blank test Carry out a blank test, using the same decomposition procedure as in 6.3, but replacing the test portion with a suitable amount of water corresponding to the amount of test portion take
32、n for analysis (6.2). 6.5 Extraction WARNING The method described in this subclause requires the use of chloroform, a toxic and ozone-depleting substance. Avoid inhalation of and exposure to this solvent. Work in a fume cupboard when handling this solvent and solutions thereof. Dispose of the waste
33、chloroform and solutions properly. Add 2 g of citric acid (3.5) to cooled digest of a sample or blank and cautiously dilute to about 25 ml with water. Add 1 ml of thymol blue indicator (3.7) and adjust to pH 8,8 by slowly adding ammonia solution (3.8), while cooling in ice bath, until the solution c
34、hanges from yellowish green to greenish blue. Transfer quantitatively to a 250 ml separator (4.6) with water, and dilute to about 150 ml. Cool the solution, and extract with two 5-ml portions of concentrated dithizone solution (3.10), shaking 1 min to 2 min each time. Continue extraction with 5-ml p
35、ortions of dilute dithizone solution (3.11) until the dithizone extract shows no change in colour. Combine the dithizone extracts in the 125 ml separator (4.6); wash with BSISO65612:20054 50 ml water, and transfer solvent to another 125 ml separator. Extract wash-water with 5 ml of chloroform (3.9)
36、and add to the dithizone extracts. Add 50 ml of dilute hydrochloric acid (3.3) to combined dithizone extracts, shake vigorously 1 min, and allow the layers to separate; discard the dithizone layer. Wash the aqueous solution with 5 ml of chloroform (3.9) and discard the chloroform. Quantitatively tra
37、nsfer the aqueous solution to a 400 ml beaker (4.3), add boiling chips, and evaporate carefully to dryness on the hot plate (4.9). Carefully rinse down sides of beaker with 10 ml to 20 ml of water and again evaporate to dryness. Dissolve the dry residue in 5,0 ml of hydrochloric acid solution (3.3).
38、 6.6 Determination 6.6.1 Preparation of the calibration graph Dilute the cadmium standard solution (3.12) with hydrochloric acid (3.3) to obtain four solutions with cadmium concentrations of 0,1 g/ml, 0,5 g/ml, 1,0 g/ml and 2,0 g/ml. Aspirate each of these solutions, in turn, into the flame of the s
39、pectrometer (4.7) using 4 times to 10 times expansion scale to obtain the maximum absorbance value for the solution having the cadmium concentration of 2,0 g/ml. Use hydrochloric acid (3.3) as a blank. Take care to keep the aspiration rate constant throughout the aspiration of each calibration solut
40、ion. Flush burner with water after each measurement. Record the corresponding values of absorbance and plot the calibration graph (absorbance against cadmium concentration in micrograms per millilitre). 6.6.2 Spectrometric measurement Set the instrument to the previously established optimum conditio
41、ns, using air-acetylene oxidizing flame and 228,8 nm resonant wavelength. Aspirate into the flame of the spectrometer (4.7) the test solution (6.5) and the blank solution (6.4), at the same aspiration rate as used for preparation of the calibration graph (6.6.1). Record the corresponding absorbances
42、. If the absorbance of the test solution is greater than for the highest standard solution used for preparation of the calibration graph (6.6.1), dilute the test solution with the hydrochloric acid (3.3) and measure the absorbance. 7 Calculation The cadmium content of the sample, expressed in millig
43、rams per kilogram, is equal to Blank () 5 cc F m (1) where c is the cadmium concentration, expressed in micrograms per millilitre, of the test solution, as read from the calibration graph; c Blankis the cadmium concentration, expressed in micrograms per millilitre, of the blank test solution, as rea
44、d from the calibration graph; BSISO65612:2005 5m is the mass, in grams, of the test portion; F is the dilution factor, if necessary. 8 Precision The precision of the method has been checked by collaborative studies of cadmium determinations in lettuce and potatoes; see Reference 2. Statistical param
45、eters have been calculated in accordance with ISO 5725; see Reference 3. Table 1 Repeatability results Type of sample Cadmium content mg/kg r amg/kg s rbmg/kg 0,1 0,04 0,01 0,5 0,17 0,06 Lettuce 1,5 0,26 0,09 0,05 0,009 0,003 0,2 0,05 0,02 Potatoes 1,0 0,09 0,03 ar is the repeatability limit. bs ris
46、 the standard deviation of repeatability. Table 2 Reproducibility results Type of sample Cadmium content mg/kg R amg/kg s Rbmg/kg 0,1 0,05 0,02 0,5 0,17 0,06 Lettuce 1,5 0,29 0,10 0,05 0,025 0,09 0,2 0,07 0,02 Potatoes 1,0 0,19 0,07 aR is the reproducibility limit. bs Ris the standard deviation of r
47、eproducibility. 9 Test report The test report shall specify: a) all information necessary for the complete identification of the sample; b) the sampling method used, if known; c) the test method used, with reference to this part of ISO 6561; d) all operating details not specified in this part of ISO
48、 6561, or regarded as optional, together with details of any incidents which may have influenced the test result(s); e) the test result(s) obtained; or, if the repeatability has been checked, the final quoted result obtained. BSISO65612:20056 Bibliography 1 AOAC Official Methods of Analysis (1995).
49、AOAC 973.34, Cadmium in Food 2 Gajan R.J., Gould J.H., Watts J.O., Fiorino J.A. Collaborative study of a method for the atomic absorption spectrophotometric and polarographic determination of cadmium in food. J. Assoc. Off. Anal. Chem., 56, No. 4, 1973, pp. 876-881 3 ISO 5725:1986, Precision of test methods Determination of repeatability and reproducibility for a standard test method by interlaboratory tests now withdrawn 4
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