BS PD CEN TS 16731-2014 Foodstuffs Determination of hydride-reactive arsenic compounds in rice by atomic absorption spectrometry (Hydride-AAS) following acid extraction《食品.pdf

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1、BSI Standards Publication Foodstuffs Determination of hydride-reactive arsenic compounds in rice by atomic absorption spectrometry (Hydride-AAS) following acid extraction PD CEN/TS 16731:2014National foreword This Published Document is the UK implementation of CEN/TS 16731:2014. The UK participation

2、 in its preparation was entrusted to Technical Committee AW/275, Food analysis - Horizontal methods. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are r

3、esponsible for its correct application. The British Standards Institution 2014. Published by BSI Standards Limited 2014 ISBN 978 0 580 83731 9 ICS 67.060 Compliance with a British Standard cannot confer immunity from legal obligations. This Published Document was published under the authority of the

4、 Standards Policy and Strategy Committee on 30 November 2014. Amendments/corrigenda issued since publication Date Text affected PUBLISHED DOCUMENT PD CEN/TS 16731:2014 TECHNICAL SPECIFICATION SPCIFICATION TECHNIQUE TECHNISCHE SPEZIFIKATION CEN/TS 16731 October 2014 ICS 67.060 English Version Foodstu

5、ffs - Determination of hydride-reactive arsenic compounds in rice by atomic absorption spectrometry (Hydride- AAS) following acid extraction Dtermination de composs arsnis ractifs aux hydrures dans le riz par spectromtrie dabsorption atomique (SAA- Gnration dHydrures) aprs extraction acide Lebensmit

6、tel - Bestimmung von Hydrid-bildenden Arsen- Verbindungen in Reis nach Sureextraktion mit Atomabsorptionsspektrometrie (Hydrid-AAS) This Technical Specification (CEN/TS) was approved by CEN on 9 September 2014 for provisional application. The period of validity of this CEN/TS is limited initially to

7、 three years. After two years the members of CEN will be requested to submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard. CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/T

8、S available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached. CEN members are the national standards bodies of Au

9、stria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Swe

10、den, Switzerland, Turkey and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels 2014 CEN All rights of exploitation in any form and by any means reserved worldwide for C

11、EN national Members. Ref. No. CEN/TS 16731:2014 E PD CEN/TS 16731:2014CEN/TS 16731:2014 (E) 2 Contents Page Foreword 3 1 Scope 4 2 Normative references 4 3 Principle 4 4 Reagents .4 5 Apparatus .5 6 Procedure .6 6.1 Sample preparation .6 6.1.1 General 6 6.1.2 Extraction .6 6.1.3 Pre-reduction of ref

12、erence, blank and sample solution 7 6.2 Atomic absorption spectrometry (Hydride generation AAS) 8 6.2.1 Operating conditions for the hydride generation AAS 8 6.2.2 AAS measurement .9 7 Evaluation .9 8 Precision .9 8.1 General 9 8.2 Repeatability .9 8.3 Reproducibility 10 9 Test report . 10 Bibliogra

13、phy . 12 PD CEN/TS 16731:2014CEN/TS 16731:2014 (E) 3 Foreword This document (CEN/TS 16731:2014) has been prepared by Technical Committee CEN/TC 275 “Food analysis - Horizontal methods”, the secretariat of which is held by DIN. Attention is drawn to the possibility that some of the elements of this d

14、ocument may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to announce this Technical Specifi

15、cation: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia,

16、Spain, Sweden, Switzerland, Turkey and the United Kingdom. PD CEN/TS 16731:2014CEN/TS 16731:2014 (E) 4 1 Scope This Technical Specification describes a screening procedure for the determination of nitric-acid extractable inorganic arsenic in rice with hydride generation-AAS. The method has been deve

17、loped and validated for the application of analysis in rice. It has been validated in an interlaboratory study according to ISO 5725 2 on parboiled rice and brown rice having an inorganic arsenic content of 0,092 mg/kg and 0,191 mg/kg. 2 Normative references The following documents, in whole or in p

18、art, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 13804, Foodstuffs Determination of elements a

19、nd their chemical species General considerations and specific requirements 3 Principle Organic and inorganic arsenic compounds are extracted from the rice using diluted nitric acid. When determining the arsenic by hydride generation technique, only reducible forms of arsenic react. Of the organic ar

20、senic compounds only a low proportion of dimethylarsinic acid reacts to form a hydride and methylarsonic acid is typically not present in rice. The gaseous hydride is transferred into a heated measuring cell (quartz cuvettes or coated graphite tube), by a stream of carrier gas, and decomposed. The a

21、bsorption line of arsenic at 193,7 nm serves as a measure of the arsenic concentration 3, 4. The procedure is exclusively applicable to rice 5. The determination of the inorganic fraction of arsenic requires a determination of arsenic with hydride generation AAS; direct measurement of the extract by

22、 graphite furnace AAS, using ICP-MS or ICP-OES provides incorrect results. 4 Reagents Unless stated otherwise, chemicals of analytical grade shall be used and “solution” means aqueous solution. The water shall be of the corresponding purity. The arsenic concentration of reagents and water shall be s

23、o low that it does not influence the result of the determination. 4.1 Hydrochloric acid, w = 30 % 1) , = 1,15 g/ml 2) . 4.2 Nitric acid, concentrated, w = 65 %. 4.3 Diluted nitric acid, c = 0,28 mol/l 3) . Dilute 3,7 ml of nitric acid (4.2) to 200 ml with water. 4.4 Sodium borohydride, w 96 %. 1) w

24、= mass fraction. 2) = mass concentration. 3) c = substance concentration. PD CEN/TS 16731:2014CEN/TS 16731:2014 (E) 5 4.5 Sodium hydroxide, w 98 %. 4.6 Sodium borohydride solution, e.g. = 3 g/l. Dissolve 1 g of sodium hydroxide pellets (4.5) in water, add 3 g of sodium borohydride (4.4) and dilute t

25、o 1 000 ml with water. Prepare the solution freshly every day of analysis. If the solution contains undissolved fractions, filter before use. The mass concentration of the sodium borohydride solution can vary depending on the system being used. Therefore, follow the manufacturers instructions. 4.7 C

26、arrier solution, diluted hydrochloric acid, e.g. w = 1,5 %. Dilute 50 ml of hydrochloric acid (4.1) to 1 000 ml with water. The mass concentration of the carrier solution can vary slightly depending on the system being used. Therefore, follow the manufacturers instructions. 4.8 L-ascorbic acid, w 99

27、,7 %. 4.9 Potassium iodide, w 99,5 %. 4.10 Solution of potassium iodide and ascorbic acid: Dilute 5 g of potassium iodide (4.9) and 5 g of ascorbic acid (4.8) in water and make up to 100 ml. Prepare the solution freshly daily. The mass concentrations of the potassium iodide and the ascorbic acid can

28、 slightly vary depending on the system being used. Therefore, follow the manufacturers instructions. 4.11 Arsenic stock solution, = 1 000 mg/l. The use of a commercial, certified stock solution is recommended. 4.12 Arsenic standard solutions: Prepare arsenic standard solutions by diluting the arseni

29、c stock solution (4.11) in several steps. The arsenic standard solutions shall contain sufficient amounts of hydrochloric acid (at least 3 ml of hydrochloric acid (4.1) per 100 ml, w = 0,9 %). Example of a dilution series: 1 000 mg/l 10 mg/l 0,1 mg/l An arsenic standard solution with a mass concentr

30、ation of = 10 mg/l of arsenic in hydrochloric acid (w = 6 %) is stable for at least one month. 4.13 Antifoaming agent, based on polydimethylsiloxane or silicone oil. 5 Apparatus In order to minimize any contaminations, pre-treat carefully all apparatus and auxiliary equipment coming into direct cont

31、act with the sample and the solutions being used, in accordance with EN 13804. If the extraction vessels are used for several times, they should be cleaned by heating to 95 C for 1 h, using nitric acid (w = 13 %). PD CEN/TS 16731:2014CEN/TS 16731:2014 (E) 6 When using glassware (e.g. Erlenmeyer flas

32、ks, beakers, graduated flasks, pipettes), ensure that it does not release any arsenic to the solutions which come into contact with the glassware. 5.1 Atomic absorption spectrometer, comprising a measurement data acquisition system and the required accessories for the hydride generation technique. 5

33、.2 Element-specific lamp for arsenic, (hollow-cathode lamp or electrode-less discharge lamp). 5.3 Centrifuge, with an acceleration of at least 1 000 g 4) . 5.4 Syringe filter (unit), pore size of 0,45 m, diameter of 25 mm, compatible for use with diluted nitric acid (4.3). 5.5 Extraction vessels, e.

34、g. 30 ml or 50 ml tubes of polypropylene, with gas-tight screw closures and sufficient pressure stability. Centrifuge tubes with screw closures are suitable. 5.6 Temperature controlled heating apparatus, for an extraction temperature of 95 C, e.g. heating block or water bath; the heating block shoul

35、d be provided with an accurately fitting insert for the vessels used. The vessels should have contact with the wall in order to ensure good heat transfer. In order to achieve an extraction temperature of 95 C, the heating block shall be adjustable to a temperature of at least 120 C. 5.7 Temperature

36、measuring device, for controlling the temperature in the extraction vessel. 6 Procedure 6.1 Sample preparation 6.1.1 General Prior to the extraction, the rice shall be finely ground, while avoiding the generation of excess heat. The particle size should be less than 500 m. The measurement should be

37、performed as soon as possible after extraction. If this is not possible, store extracts in a refrigerator but for not longer than 2 d. 6.1.2 Extraction Weigh 1 g 0,01 g of rice flour into a closable extraction vessel (5.5) and add 10 ml of diluted nitric acid (4.3). The ratio of 1:10 (test portion/e

38、xtracting agent) shall be adhered to. Close the extraction vessels tightly and mix the content intensely using a test tube shaker. There shall be no remaining lumps. Afterwards, place the vessels in a pre-heated heating block and extract for 90 min at 95 C (4 C). Alternatively, a boiling water bath

39、can be used for the extraction. The extraction time starts as soon as the temperature in the vessel reaches 95 C. Shake the vessel occasionally (one to two times during extraction) without opening. A constant stirring with a magnetic stirrer can be helpful. Additionally, prepare a blank value with 1

40、0 ml of diluted nitric acid (4.3) and treat in the same manner as the samples. The extraction temperature of 95 C (4 C) shall be reached in the extraction vessels; the measurement time starts when this temperature has been reached. It is recommended to fill a reference vessel with the same 4)g = 9,8

41、1 m/s 2 . PD CEN/TS 16731:2014CEN/TS 16731:2014 (E) 7 amount of water and to measure the temperature in the vessel by a temperature sensor (hole in the fitted lid). Experience has shown that there are differences in the temperature measured in the heating block and that measured in the solution. Alt

42、ernatively, the extraction can also be performed in a microwave-heated apparatus, using gas-tight vessels. In this case, ensure that the temperature is measured inside a reference vessel and that the sensor is calibrated for a temperature of 95 C. Measuring the temperature with infrared sensors is n

43、ot suitable for this type of extraction. Seal the vessels gas-tight in order to avoid evaporation losses and to keep the extraction volume constant. Therefore, it is no longer necessary to make the volume up to a final volume after cooling down. It shall be kept in mind that the vessels are pressuri

44、zed and that only plastics vessels shall be used which are correspondent to temperature and pressure stability. In general, polyethylene or polypropylene vessels are suitable. After the extraction, cool down the vessel and open only afterwards, if applicable. Separate the solids from the solution as

45、 soon as possible. Firstly, centrifuge the sample for 10 min, and filter through a syringe filter (5.4). The application of an ultracentrifuge (20 000 g to 25 000 g) is recommended as, in that case, filtration is no longer necessary, or considerably facilitated. It is recommended to filter just an a

46、liquot, as filtration can be very difficult due to proteins and carbohydrates in the sample. The extract shall be free of particles. The solution should be measured immediately by hydride generation AAS. If this is not possible, store the extraction solution in a suitable vessel in the refrigerator.

47、 Since new particles can be regenerated after only one day, check the extract before starting the measurement, and filter if necessary. When stored in the refrigerator (5 C to 8 C), the extract is stable for 2 d. 6.1.3 Pre-reduction of reference, blank and sample solution Depending on the hydride sy

48、stem being used, it can become necessary to use larger or smaller volumes than described as follows. The ratios stated, however, shall be adhered to. For the purpose of preparing a 1 g As/l reference solution, pipette the following solutions into the hydride generation systems analysis vessel: 200 l

49、 of the standard solution with 0,1 mg of As/l (4.12); 13,8 ml of diluted nitric acid (4.3); 2,0 ml of the potassium iodide/ascorbic acid solution (4.10); 4,0 ml of hydrochloric acid (4.1). Mix the solution after each addition. Finally, leave the vessel open or loosely covered with lintless paper, at room temperature. When preparing a 3 g As/l reference solution, take 600 l of the standard solution with 0,1 mg of As/l (4.12) and 13,4 ml of diluted nitric acid (4.3); the quantities of the other