1、Non-fatty foods - Determination of dithiocarbamate and thiuram disulfide residues - Part 3: UV spectrometric xanthogenate method The European Standard EN 123963:2 has the status of a British Standard ICs 67.060 BS EN 12396-3:ZOOO NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGET LAW
2、 STD-BSI BS EN 1239b-3-ENGL 2000 M Lb24bb9 OBb24bL 541 W BS EN 12396-3:2000 been prepared under the direction of the Consumer AmdNo. Date Products and SeMces Sector Committee, was published under the authority of the standards Committee and comes inta effect on 15 August 2000 O ES1 082000 ISBN O 580
3、 34878 4 National foreword Comments This British Standard is the official English ianguage version of EN 1239632000. The UK participation in its preparation was entrusted to Technical Committee AW/-/3, Food anaiysii - Horizontal methods, which has the responsibility to: - aid enquirers to understand
4、 the text; - present to the responsible European committee any enquiries on the - monitor related international and European developments and promulgate interpretation, or proposals for change, and keep the UK interests informed; them in the UK. A list of organizations represented on this committee
5、can be obtained on request to its secrem. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled Intedonal Standards Correspondence Index“, or by using the “Find
6、“ facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to hclude all the necessary provisions of a contmct. Users of British standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal ob
7、ligations. Summary of pages This document comprises a front cover, an inside front cover, the EN title page, pages 2 to 11 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. STD.BS1 BS EN 1239b-3-ENGL 2000 M Lh24hb 08b2462 Lia Part 2: G
8、as chromatographic method; Part 3: UV spectrometric xanthogenate method. Annex A is informative. According to the CENKENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark,
9、 Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. O BSI 08-2000 Page 3 EN 12396-312000 1 Scope This European Standard specifies a UV spectrometric method for the determination of low-level residue
10、s of dithiocarbamate and thiuram disulfide fungicides as xanthogenates. Dithiocarbamate and thiuram disulfide fungicides release carbon disulfide under specified conditions (e.g. mancozeb, maneb, propineb, thiram, zineb). It is applicable to such compounds especially in and on those foodstuffs of pl
11、ant origin for which low maximum residue levels have been set. Only the quantification of the whole group is possible using this method and not the identification of individual compounds. Generally the maximum residue levels (MRLs) are expressed in terms of carbon disulfide. 2 Normative references T
12、his European Standard incorporates, by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these pub
13、lications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. IS0 1750 EN 12393-1 :1998 EN 12396-1 :I 998 EN 12396-2:1998 Pesticides and other agrochemicals - Common names. Non-fatty
14、foods - Multiresidue methods for the gas chromatographic determination of pesticide residues - Part 1 : General considerations. Non-fatty foods - Determination of dithiocarbamate and thiuram disulfide residues - Part 1 : Spectrometric method. Non-fatty foods - Determination of dithiocarbamate and th
15、iuram disulfide residues - Part 2: Gas chromatographic method. 3 Principle The sample is heated with hydrochloric acid and tin(ll)chloride to release carbon disulfide from any dithiocarbamates and/or thiuram disulfides present. The carbon disulfide is separated and purified by distillation and colle
16、cted in a methanolic potassium hydroxide solution. Under these conditions, carbon disulfide forms potassium xanthogenate. The absorption of this reaction product is measured spectrometrically at a wavelength of 302 nm with base line correction at wavelengths of 272 nm and 332 nm. The mass fraction o
17、f dithiocarbamate and/or thiuram disulfide residues is calculated and expressed in terms of milligrams of carbon disulfide per kilogram of foodstuff. For further information on this method, see l, 2, 3. 4 Reagents 4.1 General Unless otherwise specified, use reagents of recognized analytical grade, p
18、referably for pesticide residue analysis, and distilled or demineralized water. Label all standard containers with the name and purity of all pesticides. For the full chemical names and structures, see IS0 1750. Take every precaution to avoid possible contamination of water, solvents, inorganic salt
19、s etc. by plastics and rubber materials. Use only glass containers for storage and handling of all water and reagents. 4.2 Carbon disulfide, colouriess, mass fraction of at least 99%. If stored at -20 OC it is stable for 2 years to 3 years. 4.3 Methanol. 4.4 Hydrochloric acid, concentrated, mo(HCI)
20、= 1,16 glml. 4.5 Sulfuric acid, concentrated, no(HzS04) = 1,84 g/ml. 0 BSI 08-2000 Page 4 EN 12396-3:2000 4.6 Sodium hydroxide solution, p(Na0H) = 1 O0 gil). 4.7 Potassium hydroxide methanolic solution I, p(K0H) = 28 g/l in methanol (4.3). 4.8 Potassium hydroxide methanolic solution II, p(K0H) = 56
21、gll in methanol (4.3). 4.9 Tin(ll) chloride solution, p(SnCI2.2H20) = 40 g/lOO ml in concentrated hydrochloric acid (4.4). 4.10 Tin(ll) chloride - hydrochloric acid solution, p(SnCI2.2H20) = 3,3 g/100 ml. Mix 20 ml of tin(ll) chloride solution (4.9) with 20 ml of concentrated hydrochloric acid (4.4)
22、 and carefully add 200 ml of water. 4.1 1 Carbon disulfide stock solution Weigh to the nearest 10 mg a stoppered 50 ml volumetric flask with a ground glass neck containing 40 ml of methanol (4.3). Add approximately 1 ml of carbon disulfide (4.2) (equivalent to approximately 1,25 g) using a pipette,
23、close the flask at once and re-weigh to the nearest 10 mg to obtain the exact mass of carbon disulfide by difference. Dilute to the mark with methanol and mix well. Prepare freshly for each calibration curve. 4.12 Carbon disulfide standard solution Dilute I ml of carbon disulfide stock solution (4.1
24、 I) with methanol (4.3) to 25 ml in a volumetric flask. Dilute 1 ml of this solution with methanol to 100 ml in a volumetric flask. I ml of this standard solution is equivalent to approximately 10 pg of carbon disulfide. Prepare freshly for each calibration curve. 5 Apparatus 5.1 General Thoroughly
25、clean glassware shall be used. See 5.1 of EN 12393-1:1998 for the cleaning of glassware. 5.2 Decomposition and distillation apparatus, consisting of a 1 I or a 2 I round bottomed three necked flask or cylindrical flask with a three necked adapter, a dropping funnel, a gas inlet tube, an ascending Li
26、ebig condenser, four absorption tubes, the last two preferably fitted with a Widmer helix, connected by spherical socket joints, the first being attached to the Liebig condenser (see Figure I). _ 1) pis the mass concentration. l i Q BSI 08-2000 Page 5 EN 12396-312000 1 = Liebig condenser 2 = droppin
27、g funnel 3 = gas inlet tube 4 = cylindrical flask or round bottomed flask 5 = absorption tubes 6 = Widmer helix Figure 1 : Decomposition and distillation apparatus 5.3 Flowmeter. 5.4 Heating mantle, electrically operated, at least 450 W; or gas burner fitted with a Babo funnel and flask holder. 5.5
28、Spectrometer, suitable for measurements at wavelengths from 270 nm to 350 nm, with 1 cm quartz cells. A double beam spectrometer should preferably be used. 5.6 Low vacuum pump, attached to the last absorption tube, or a source of nitrogen under pressure, attached to the gas inlet tube. 6 Sampling Pr
29、epare the laboratory sample according to a generally recommended method of sampling to achieve a representative part of the product to be analyzed. NOTE: Sampling procedures for the official control of pesticide residues in and on fruits and vegetables are given in EEC Directive 79/700/EEC 4. 7 Prep
30、aration of the samples 7.1 Test sample If the sample reaches the laboratory frozen, store it at -20 OC before analysis. Where possible, carry out the analysis of fresh samples immediately after their arrival in the laboratory. Do not analyze a laboratory sample which is wholly or extensively spoiled
31、. Q BSI 08-2000 STDmBSI BS EN L239b-3-ENGL 2000 = Lb24bbS OBb24b7 TbT Page 6 EN 12396-3:2000 For analysis take only the portion of the laboratory sample to which the maximum residue limit applies. No further plant-parts may be removed. A record of the plant-parts which have been removed shall be kep
32、t. The sample thus prepared is the analytical sample. If the sample cannot be analyzed immediately, store it at O OC to 5 OC for no longer than 2 days before analysis. The reduction of the analytical sample shall be carried out in such a way that representative portions are obtained (e.g. by divisio
33、n into four and selection of opposite quadrants). When the samples are in small units (e.g. small fruits, vegetables, cereals), the analytical sample shall be thoroughly mixed before weighing out the test portion. When the samples are in larger units, take wedge-shaped sections (e.g. large fruits an
34、d vegetables) or cross- sections (e.9. cucumbers) which include the outer surface from each unit. NOTE: The residues of dithiocarbamates and thiuram disulfides, which are on the surface of the plant-parts and are not systemic, decompose rapidly especially in chopped samples. Therefore precautions sh
35、ould be taken to avoid decomposition. If samples have to be stored for more than 2 days, they shall be deep-frozen at -20 “C. To ensure that even after thawing representative samples can be taken, prepare portions of the product which are each sufficient for one analysis. 7.2 Test portion Weigh out
36、test portions of masses up to 200 g to an accuracy of I1 %. After weighing out the test portion, remove certain parts which would interfere with the analytical procedure. In the case of stone fruits, the stones may be removed after weighing out. The basis for the calculation of the residue mass frac
37、tion is the mass of the original test portion (with stones). The test portion shall not be cut or reduced to smaller pieces than can just pass through the neck of the reaction flask, as the residues of dithiocarbamates and thiuram disulfides fall the more the test portion is cut. Analyze the test po
38、rtion immediately after cutting. 8 Procedure 8.1 Safety aspects WARNING: Many dithiocarbamates, thiuram disulfides and carbon disulfide are toxic by various routes of exposure, especially in concentrated form. When working with dithiocarbamates, thiuram disulfides and carbon disulfide consult safety
39、 data sheets of the manufacturer for information. Vapours from some volatile solvents are toxic. Several of these solvents are readily absorbed through skin. Use effective fume hoods to remove vapours of these solvents as they are set free. 8.2 Preparation of blanks Prepare reagent and matrix blanks
40、. Spiked recovery tests at levels appropriate to the maximum residue levels shall be carried out and shall lead to satisfying results. The absorption for the reagent blanks measured at a wavelength of 302 nm against the methanolic potassium hydroxide solution I (4.7) shall be zero or near zero. NOTE
41、 1 : Analysts should thoroughly familiarize themselves with the method before starting the analysis. NOTE 2: Some vegetables (e.g. of the family Cruciferae) contain naturally occurring compounds which release carbon disulfide under the conditions described in this European Standard. Therefore the an
42、alysis of such vegetables can lead to false positive results. Q BSI 08-2000 Page 7 EN 12396-3:2000 8.3 Preparation of the calibration curve Add 5 ml of methanolic potassium hydroxide solution II (4.8) to each of sixteen 10 ml volumetric flasks. Then add 0,l ml, 0,2 ml, 0,4 ml, 0,8 ml, 1,2 ml, 1,6 ml
43、, 2 ml and 4 ml of the carbon disulfide standard solution (4.12) (equivalent to 1 pg, 2 pg, 4 pg, 8 pg, 12 , 16 ,ug, 20 pg and 40 ,ug of CS2) from a graduated pipette or a burette to each of two volumetric flasks. Dilute to the mark with methanol, mix well, and let the 16 mixtures stand for 45 min.
44、Perform the spectrometric measurement as described in 8.4.3. Plot the values obtained for the corrected absorption on the ordinate (y axis) against the mass of carbon disulfide in each mixture on the abscissa (x axis) to obtain a calibration curve. The calibration curve shall be linear over the rang
45、e 1 pg to 40 pg carbon disulfide. If these requirements are not fulfilled, prepare a new calibration curve using a freshly prepared set of reaction mixtu res. Alternatively carry out a regression analysis on the 16 values and plot the regression line as the calibration curve. 8.4 Measurement of the
46、sample 8.4.1 Preparation of the apparatus Add 20 ml of sodium hydroxide solution (4.6) to the first absorption tube in the decomposition and distillation apparatus (see Figure 1) and 20 ml of sulfuric acid (4.5) to the second. To the third and the fourth absorption tubes, fitted with a Widmer helix,
47、 add 8 mi each of methanolic potassium hydroxide solution I (4.7). These tubes shall be cooled with ice water, to avoid losses of methanol. NOTE: The fourth absorption tube containing methanolic potassium hydroxide solution is attached to check the complete absorption of the evolved carbon disulfide
48、. Turn on the water flow through the reflux condenser and adjust the nitrogen flow or the low vacuum pump (5.6) to give approximately 150 ml of nitrogen or air per minute passing through the absorption tubes. 8.4.2 Decomposition and distillation Add a test portion of up to 200 g to the three necked
49、flask (400 g in case of baby food). Close the apparatus. Take care to avoid any losses of carbon disulfide from the apparatus. Then add 240 ml of tin(ll) chloride-hydrochloric acid solution (4.10) through the dropping funnel. If the amount of liquid is not enough for a sample of bulky crop material (e.g. lettuce) to be fully immersed, add more tin(ll) chloride-hydrochloric acid solution. Then immediately heat flask contents rapidly to boiling. To reach this rapidly, especially if the material to be analyzed is deep frozen, heat the tin(ll) chloride-hydrochloric acid soluti
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