EN 15517-2008 en Foodstuffs - Determination of trace elements - Determination of inorganic arsenic in seaweed by hydride generation atomic absorption spectrometry (HGAAS) after aci.pdf

1、BRITISH STANDARDBS EN 15517:2008Foodstuffs Determination of trace elements Determination of inorganic arsenic in seaweed by hydride generation atomic absorption spectrometry (HGAAS) after acid extractionICS 67.050g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g

2、44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN 15517:2008This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 March 2008 BSI 2008ISBN 978 0 580 56950 0National forewordThis

3、 British Standard is the UK implementation of EN 15517:2008.The UK participation in its preparation was entrusted to Technical Committee AW/-/3, Food analysis Horizontal methods.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does no

4、t purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.Amendments/corrigenda issued since publicationDate CommentsEUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NO

5、RMEN 15517March 2008ICS 67.050English VersionFoodstuffs - Determination of trace elements - Determination ofinorganic arsenic in seaweed by hydride generation atomicabsorption spectrometry (HGAAS) after acid extractionProduits alimentaires - Dosage des lments traces -Dosage de larsenic inorganique d

6、ans les algues marinespar spectromtrie dabsorption atomique par gnrationdhydrures (SAAGH) aprs extraction acideLebensmittel - Bestimmung von Elementspuren -Bestimmung von anorganischem Arsen in Meeresalgen mitAtomabsorptionsspektrometrie-Hydridtechnik (HGAAS)nach SureextraktionThis European Standard

7、 was approved by CEN on 7 February 2008.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such

8、nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and

9、 notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg,

10、Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels 2008 CEN All rights of expl

11、oitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 15517:2008: EEN 15517:2008 (E) 2 Contents Page Foreword3 1 Scope 4 2 Normative references 4 3 Principle4 4 Reagents.5 5 Apparatus and equipment 6 6 Procedure .7 7 Calculation9 8 Precision.9 9 Test report 10

12、Annex A (informative) Results of the inter-laboratory tests .11 Bibliography 14 BS EN 15517:2008EN 15517:2008 (E) 3 Foreword This document (EN 15517:2008) has been prepared by Technical Committee CEN/TC 275 “Food analysis - Horizontal methods”, the secretariat of which is held by DIN. This European

13、Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by September 2008, and conflicting national standards shall be withdrawn at the latest by September 2008. Attention is drawn to the possibility that some of the elem

14、ents of this document 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 implement this Eu

15、ropean Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the Unit

16、ed Kingdom. BS EN 15517:2008EN 15517:2008 (E) 4 1 Scope This document specifies a procedure for the determination of hydrochloric acid (gastric acid concentration) extractable inorganic arsenic in seaweed. Collaborative studies have been carried out (Annex A). The method is suitable for the determin

17、ation of inorganic arsenic not less than 1 mg/kg and below 100 mg/kg on a dry weight basis. The amount of inorganic arsenic is considered to be that part determined by the procedure described in this document. 2 Normative references The following referenced documents are indispensable for the applic

18、ation of this document. 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 trace elements Performance criteria, general considerations and sample prepara

19、tion 3 Principle Arsenic compounds are extracted from the sample by diluted hydrochloric acid (in accordance with EN 71-3 5) and the arsenic in the extract is determined by hydride generation AAS. In acidic media inorganic compounds of arsenic(III) and arsenic(V) as well as the monomethylarsonic aci

20、d (MMA) and dimethylarsinic (cacodylic) acid (DMA) form a volatile hydride with sodium borohydride. There is no reaction of the stable organic arsenic compounds like arsenosugar, arseno-betaine and arseno-choline under these conditions. The gaseous hydride is transferred into a heated measuring cell

21、 (cuvette) by means of a carrier gas stream and decomposed. The absorption at 193,7 nm (arsenic line) serves as a measure of arsenic concentration. The hydride signal sensitivity of DMA reaches generally low rates as compared to As(III). The contribution of MMA in the hydride signal can be neglected

22、, since MMA occurs in seaweed only in small amounts. The hydride generation AAS in combination with this hydrochloric acid extraction may be used as nearly selective method of determination for inorganic arsenic. Generation of arsine from As(III) is much faster and gives greater sensitivity than gen

23、eration from As(V) and is also less subject to interference. Arsenic(V) shall be reduced to arsenic(III) (pre-reduction) in order to avoid incorrect measurements. BS EN 15517:2008EN 15517:2008 (E) 5 4 Reagents 4.1 General The concentration of arsenic in the reagents and water used shall be low enoug

24、h not to affect the results of the determination. 4.2 Hydrochloric acid, mass fraction w = 30 %, mass concentration (HCl) = 1,15 g/ml. 4.3 Hydrochloric acid solution, substance concentration c = (0,07 0,005) mol/l. 4.4 Hydrochloric acid, approximately c = 2 mol/l. 4.5 Sodium borohydride, w 96 % 4.6

25、Sodium hydroxide, w 98 % 4.7 Sodium borohydride solution, e.g. substance concentration c = 2 g/l (example for using the flow injection procedure described under 6.2.1 (b). Dissolve 2 g of sodium hydroxide pellets in water, add 2 g of sodium borohydride and dilute to 1 000 ml with water. A fresh solu

26、tion shall be prepared daily and filtered before use. The concentration by mass of the sodium borohydride solution may vary with the system and the instructions of the relevant manufacturer shall therefore be observed. 4.8 Diluted hydrochloric acid, e.g. mass fraction w 3 % (carrier solution, only f

27、or use in the flow injection procedure). Dilute approximately 90 ml of hydrochloric acid (4.2) to 1 000 ml with water. The concentration by mass of the carrier solution may vary with the system and the instructions of the relevant manufacturer shall therefore be observed. 4.9 L-Ascorbic acid, w(C6H8

28、O6) 99,7 % 4.10 Potassium iodide, w(KI) 99,5 % 4.11 Potassium iodide/ascorbic acid solution Dissolve 3 g of potassium iodide and 5 g of ascorbic acid in water and dilute to 100 ml. Prepare a fresh solution daily. The concentrations of the potassium iodide and ascorbic acid may vary slightly with the

29、 system and the instructions of the relevant manufacturer shall therefore be observed. 4.12 Diarsenic trioxide (As2O3), w(As2O3) 99,5 % 4.13 Arsenic stock solution, with an arsenic mass concentration of 1000 mg/l. If commercial stock solutions are not available, proceed as follows: dissolve 1,320 g

30、of diarsenic trioxide BS EN 15517:2008EN 15517:2008 (E) 6 (4.12) in 25 ml of potassium hydroxide solution ( = 20 g/100 ml), neutralize with 20 % (mass fraction) sulfuric acid with phenolphthalein as indicator and dilute to 1 000 ml with 1 % (mass fraction) sulfuric acid. 4.14 Arsenic standard soluti

31、ons Dilute the arsenic stock solution (4.13) in several steps. The arsenic standard solutions shall contain an adequate amount of hydrochloric acid, e.g. 2 ml of hydrochloric acid (4.2) per 100 ml. Example of a dilution series: 1000 mg/l 100/550 mg/l 50/55 mg/l 50/10,1 mg/l A standard solution of 5

32、mg/l arsenic in 0,6 % (mass fraction) hydrochloric acid is stable for at least one week. 4.15 Arsenic calibration solutions Prepare five calibration solutions in the required calibration range from the standard solution of 0,1 mg/l (4.14), ensuring that the concentrations of the calibration solution

33、s are not outside the linear range of the calibration function and are also in the expected sample content range. The concentration of acid in the calibration solutions shall be equal to that in the sample solution. Example for the 1 g/l to 10 g/l range: 0,1 mg/l 100/11 g/l 100/33 g/l 100/55 g/l 100

34、/88 g/l 100/1010 g/l The calibration solutions may also be prepared from the appropriately diluted standard solution in the measurement vessel itself by adding the reagents for the pre-reduction (see 6.1.3). Prepare fresh calibration solutions daily. The following procedure is recommended for the pr

35、eparation of standard and calibration solutions: pour some water into the volumetric flask and add the requisite amount of acid. After cooling to room temperature, add the stock or standard solution using a pipette and dilute to the mark with water. 4.16 Zero member compensation solution, containing

36、 water and acid in a concentration equal to that in the sample solution. 5 Apparatus and equipment 5.1 General To minimise the contamination, all apparatus that come into direct contact with the sample and the solutions shall be carefully pre-treated according to EN 13804. BS EN 15517:2008EN 15517:2

37、008 (E) 7 5.2 Atomic absorption spectrometer, with measurement recording system and accessories for the hydride generation method. 5.3 Element-specific lamp (hollow-cathode or electrodeless discharge lamp) for arsenic. 5.4 Centrifuge 5.5 Syringe filter (unit), pore size 0,45 m, diameter 25 mm, resis

38、tant to hydrochloric acid (4.4). Membranes of polyester or nylon have been proven suitable. 5.6 Indicator paper 5.7 Device for thermostating, at approximately 37 C. 5.8 Stirrer or shaking machine 6 Procedure 6.1 Sample preparation 6.1.1 General It is possible that extracted arsenic compounds are dec

39、omposed to inorganic arsenic, even when stored in a refrigerator. Therefore, determination by hydride generation AAS should be conducted as soon as possible, latest within one week. 6.1.2 Hydrochloric acid extraction In imitation of EN 71-3 the well homogenized sample is weighed (minimum weighed por

40、tion 0,2 g) into a vessel, which is suitable for the extraction and allows sufficient agitation motion. The ratio of weighed portion to extracting agent (extractant) shall be 1:50 (1 part + 49 parts). Add the appropriate amount of hydrochloric acid solution (4.3) of approximately 37 C to the sample

41、and mix for 1 min. Transfer one drop of this mixture onto indicator paper. If the pH is more than 1,5, add dropwise hydrochloric acid (4.4) while stirring until the pH value lies between 1,0 and 1,5. Continuously agitate (by stirring or shaking) the suspension at a temperature of approximately 37 C

42、for 1 h and then allow it to stand for 1 h at approximately 37 C. Immediately afterwards solids shall be separated from the solution. First centrifuge for 10 min and then filter through a syringe filter (5.5). The extract shall be free of particles. The concentration of arsenic in the solution shoul

43、d be measured by hydride generation AAS as soon as possible. The extraction solution is stored in a suitable vessel in a refrigerator until measurement. 6.1.3 Pre-reduction Depending on the hydride system used, it may be necessary to use larger or smaller volumes than described below. The ratios spe

44、cified shall, however, be maintained. Introduce and thoroughly mix 2 ml of calibration solution (4.15) and 2 ml of hydrochloric acid (4.2) into the measurement vessel of the hydride system. Then add 1 ml of potassium iodide/ascorbic acid solution (4.11) and again mix thoroughly. After leaving for 45

45、 min at room temperature in an open vessel, dilute to 10 ml with water and mix thoroughly to obtain a solution ready for measuring. If the calibration solution is prepared in the measurement vessel itself, use the appropriate quantity of standard solution and dilute to 2 ml with the zero member comp

46、ensation solution (4.16), then proceed as described above. Treat the zero member compensation and the sample solutions in the same way. Up to 2 ml hydrochloric acid extract according to 6.1.2 are used for the pre-reduction. If necessary, the dilutions are made with zero member compensation solution

47、(4.16) prior to the pre-reduction. Compensate using less than 2 ml of sample solution by adding the appropriate amount of zero member compensation solution (4.16). BS EN 15517:2008EN 15517:2008 (E) 8 The acid and reducing-agent concentrations shall be the same in all the test solutions. Only seal th

48、e measurement vessels after diluting with water for the final mixing. Do not analyse yellow-coloured solutions as they give incorrect results (too low or too high). To avoid problems in the pre-reduction, do not pipette more than 20 solutions in one series. IMPORTANT The proportion of the inorganic

49、arsenic can be up to 90 % of the total arsenic content in the sample. It has been proven convenient to determine first the total arsenic content of the sample in order to use an appropriate dilution of the hydrochloric acid extract for the pre-reduction. Since the measurement solution may foam in the hydride system, take care when using non-diluted hydrochloric acid extracts for pre-reduction! 6.2 Atomic absorption spectrometry (hydride generation AAS) 6.2.1 Working conditions for AAS