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1、 Reference number ISO 6561-2:2005(E) ISO 2005 INTERNATIONAL STANDARD ISO 6561-2 First edition 2005-02-01 Fruits, vegetables 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 ca
2、dmium Partie 2: Mthode par spectromtrie dabsorption atomique avec flamme Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 02:37:44 MDTNo reproduction or networking permitted without license from I
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6、 address given below. ISO 2005 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
7、 ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2005 All rights reserved Copyright International Organization for Standardiza
8、tion Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 02:37:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6561-2:2005(E) ISO 2005 All rights reserved iii Foreword ISO (the International Organization for Standardization
9、) 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. Each member body interested in a subject for which a technical committee has been established has the right to be repr
10、esented on that committee. International organizations, governmental and 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. International Standards ar
11、e 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 Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an Internation
12、al 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 subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 6561-2 was pr
13、epared 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 and replaces ISO 6561:1983, which has been technically revised. ISO 6561 consists of the following parts, under the genera
14、l title Fruits, vegetables and derived products Determination of cadmium content: Part 1: Method using graphite furnace atomic absorption spectrometry Part 2: Method using flame atomic absorption spectrometry Copyright International Organization for Standardization Provided by IHS under license with
15、 ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 02:37:44 MDTNo reproduction or networking permitted without license from IHS -,-,- Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 02
16、:37:44 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISO 6561-2:2005(E) ISO 2005 All rights reserved 1 Fruits, vegetables and derived products Determination of cadmium content Part 2: Method using flame atomic absorption spectrometry 1 Scope This pa
17、rt of ISO 6561 specifies an atomic absorption spectrometric method 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
18、This method is based on the decomposition of organic matter with HNO3, H2SO4 and H2O2, extraction of cadmium by dithizone-CHCl3 at pH 9, and determination of cadmium by flame atomic absorption spectrometry. 3 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and
19、water which has been distilled twice in borosilicate glass 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 (2
20、0 = 1,19 g/ml) into a 1 000 ml one-mark volumetric flask 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
21、with 4,3 ml of sodium hydroxide solution (3.6). Dilute to 200 ml in a flask with water. 3.8 Ammonia solution, 28 % to 30 % solution. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 02:37:44 MDTNo
22、 reproduction or networking permitted without license from IHS -,-,- ISO 6561-2:2005(E) 2 ISO 2005 All rights reserved 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
23、dithizone solution (3.10) 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 gl
24、asses during all operations. 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
25、 flasks, of capacities 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 mant
26、le. 4.9 Hot plate. 4.10 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
27、 Standard dealing with the product concerned, it is recommended that the parties concerned come to an agreement on the subject. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 02:37:44 MDTNo repr
28、oduction or networking permitted without license from IHS -,-,- ISO 6561-2:2005(E) ISO 2005 All rights reserved 3 6 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 mechanical grind
29、er (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). 6.3 De
30、composition 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 nitric a
31、cid (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 cooling
32、 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 (3.4), 1
33、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 SO3 fumes, adding more hydrogen peroxide (3.4) as required, to remove char. Heat v
34、igorously 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 taken for an
35、alysis (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 chlorofo
36、rm 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 changes f
37、rom 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 portions
38、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 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Res
39、ale, 04/23/2007 02:37:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6561-2:2005(E) 4 ISO 2005 All rights reserved 50 ml water, and transfer solvent to another 125 ml separator. Extract wash-water with 5 ml of chloroform (3.9) and add to the dithizone extracts. Add
40、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 transfer the aqueous solution to a 400 ml
41、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). 6.6 Determination 6.6.1 Preparation of
42、 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 spectrometer (4.7) using 4 times to 10 t
43、imes 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 solution. Flush burner with water after each
44、 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 conditions, using air-acetylene oxidizing flame
45、 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. If the absorbance of the test solutio
46、n 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 milligrams per kilogram, is equal to Blank ()
47、5cc F m (1) where c is the cadmium concentration, expressed in micrograms per millilitre, of the test solution, as read from the calibration graph; cBlank is the cadmium concentration, expressed in micrograms per millilitre, of the blank test solution, as read from the calibration graph; Copyright I
48、nternational Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 02:37:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6561-2:2005(E) ISO 2005 All rights reserved 5 m 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 determination