BS 6534-1984 Method for quantitative determination of lead in tin coatings《锡涂料的铅定量测定方法》.pdf

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1、BRITISH STANDARD BS6534:1984 Method for Quantitative determination of lead in tin coatings UDC669.68:543.422.062:546.815BS6534:1984 This BritishStandard, having been prepared under the directionof the Furniture and Household Equipment StandardsCommittee, was published under the authority ofthe Board

2、 of BSI and comesintoeffect on 28 September1984 BSI12-1999 The following BSI references relate to the work on this standard: Committee reference FHM/12 Draft for comment83/38300DC ISBN 0 580 14007 5 Committees responsible for this BritishStandard The preparation of this BritishStandard was entrusted

3、 by the Furniture and Household Equipment Standards Committee (FHM/-) to Technical Committee FHM/12 upon which the following bodies were represented: Association of Public Analysts Consumer Standards Advisory Committee of BSI Department of Education and Science Department of Trade and Industry (Cons

4、umer Safety Unit, CCS Division) Department of Trade and Industry (Laboratory of the Government Chemist) Department of Trade and Industry (National Weights and Measures Laboratory) International Tin Research Institute Metal Finishing Association National Hardware Alliance Amendments issued since publ

5、ication Amd. No. Date of issue CommentsBS6534:1984 BSI 12-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Preparation of test pieces 2 7 Procedure 2 8 Expression of results and reproducibility of the meth

6、od 3 9 Test report 3 Publications referred to Inside back coverBS6534:1984 ii BSI 12-1999 Foreword This BritishStandard has been prepared under the direction of the Furniture and Household Equipment Standards Committee and was primarily developed for use in conjunction with BS3788 to provide a quant

7、itative method for the determination of lead in the coating on these utensils. The method may be used to determine the proportion of lead in tin coatings for the purposes of The Cooking Utensils (Safety) Regulations1972 (SI1972 No.1957). A British Standard does not purport to include all the necessa

8、ry provisions of a contract. Users of British Standards are responsible for their 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, pagesi andii, pages1 to4

9、, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS6534:1984 BSI 12-1999 1 1 Scope This BritishStandard describes a method for the quantitativ

10、e determination of lead in tin coatings on ferrous or copper base articles, typically culinary utensils. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this BritishStandard the following definitions apply. 2.1 cu

11、linary utensil an article used in the preparation and/or cooking of food 2.2 tin coated ware an article manufactured from tinplate or having a tin coating applied to a substrate metal by electrodeposition, hot dipping or other process after manufacture of the article 3 Principle The coating is selec

12、tively stripped from test pieces of the tin coated ware by means of an appropriate acid or acid mixture. The lead and tin contents of the resulting solution are measured by means of atomic absorption spectroscopy. A concentration step may be performed to aid the determination of low amounts of lead.

13、 Lead in the coating is calculated as a percentage of tin found. 4 Reagents All reagents shall be of recognized analytical quality unless otherwise specified. 4.1 Water, complying with the requirements of BS3978. 4.2 Acetone 4.3 Tin metal 4.4 Lead metal 4.5 Copper sulphate, CuSO 45H 2 O. 4.6 Tartari

14、c acid 4.7 Hydrochloric acid (density1.18g/mL), low in lead for foodstuffs analysis. 4.8 Nitric acid solution (50% V/V). To500mL of water add500mL of nitric acid (density1.42g/mL). (Smaller quantities may be prepared.) 4.9 Copper sulphate solution (0.5% M/V). Dissolve5g of copper sulphate(4.5) in1L

15、of hydrochloric acid(4.7). (Smaller quantities may be prepared.) 4.10 Acid mixture. To350mL of water add250mL of hydrochloric acid(4.7),400mL of nitric acid solution(4.8) and50g of tartaric acid(4.6). (Smaller quantities may be prepared.) 4.11 Standard metal solutions 4.11.1 General. These may be pr

16、epared as described in4.11.2 and4.11.3; alternatively, appropriate commercially available standardized atomic absorption spectrometric stock solutions may be used. 4.11.2 Tin solution1mL=10mg Sn. Dissolve1.00g of tin metal(4.3) in60mL of hydrochloric acid(4.7) (a few drops of nitric acid solution(4.

17、8) may be required to facilitate dissolution). Transfer quantitatively to a100mL volumetric flask and make up to the mark with water. 4.11.3 Lead solution 1mL=1mg Pb. Dissolve0.100g of lead metal(4.4) in a mixture of5mL of nitric acid solution(4.8) and15mL of water. Transfer quantitatively to a100mL

18、 volumetric flask and make up to the mark with water. This solution is diluted with water to give the following solutions: a) 1mL=0.1mg Pb; b) 1mL=0.01mg Pb. Prepare solutions a) and b) immediately before use. 5 Apparatus 5.1 Balance, with a capacity of100g and to an accuracy of0.001g. 5.2 Flame ato

19、mic absorption spectrometer, set up according to the manufacturers operating instructions; an air-acetylene flame is satisfactory for the determination of tin by this method. 5.3 Laboratory glassware, of borosilicate or other equivalent lead-free glass. Volumetric glassware shall be of class A accur

20、acy according to BS700, BS846 or BS1792 as appropriate. 5.4 Burette, graduated in0.02mL or appropriate pipettes (see7.3.1 and7.6.1).BS6534:1984 2 BSI 12-1999 6 Preparation of test pieces Cut, stamp or punch pieces from the selected article, without damaging or contaminating the surface, to give test

21、 pieces with a tin coated surface area of approximately1000mm 2 . Prepare sufficient of these pieces to give approximately0.1g of tin coating(see7.1.6 and7.2.6) for the test. In the case of small articles, or those with very thin coatings, it may be necessary to use the whole article. For large arti

22、cles take replicate samples from representative areas of the article such that not less than20% of the surface has been tested. Do not take test pieces from areas which include a solder seam. If the test piece from a culinary utensil possesses an area of its surface which is not intended to come int

23、o contact with foodstuffs, cover this area by a protective coating after the initial degreasing(see7.1.1 or7.2.1). NOTECertain paints and varnishes have been found suitable to provide this protection but prior testing of any material should be carried out to ensure that adhesion properties are adequ

24、ate and that no lead contamination can occur during the stripping procedure. 7 Procedure 7.1 Removal of the coating from ferrous base articles 7.1.1 Degrease the test pieces with hot acetone(4.2). NOTESome articles may be lacquered in manufacture. This lacquer film may not necessarily be soluble in

25、hot acetone and, if required, other solvent systems shown not to attack the tin coating may be used to remove the lacquer film. 7.1.2 When completely dry, weigh the test pieces. 7.1.3 Place the test pieces in20mL of copper sulphate solution(4.9) and leave until effervescence has almost ceased, then

26、rub the surfaces of the test pieces with a “rubber policeman” to remove precipitated copper. 7.1.4 Return the test pieces to the solution and leave for5min. 7.1.5 Remove the test pieces from the solution and rinse with distilled water, collecting the rinsings in the same beaker as the solution. 7.1.

27、6 Dry and weigh the test pieces and calculate the approximate mass of tin coating removed. This mass is not sufficiently accurate for the calculation of the percentage of lead because of the deposition of copper and the dissolution of trace amounts of the substrate, but provides guidance to ensure t

28、hat approximately0.1g of tin coating has been obtained. 7.1.7 Add5mL of nitric acid solution(4.8) to the solution and heat to dissolve the precipitated copper metal. 7.1.8 Cool and transfer quantitatively to a50mL volumetric flask; make up to the mark with water. Use this solution to determine lead

29、as described in7.4. 7.1.9 Transfer10.0mL of the solution(see7.1.8) to a50mL volumetric flask, add16mL of copper sulphate solution(4.9),4mL of nitric acid solution(4.8) and make up to the mark with water. Use this solution to determine tin as described in7.4. 7.1.10 Repeat the test procedure omitting

30、 the test pieces to provide a blank determination. 7.2 Removal of the coating from copper base articles 7.2.1 Degrease the test pieces with hot acetone(4.2)(see note to7.1.1). 7.2.2 When completely dry, weigh the test pieces. 7.2.3 Place the test pieces in20mL of hydrochloric acid(4.7). 7.2.4 Heat t

31、o near boiling until all the coating has been removed as denoted by the appearance of the copper substrate. 7.2.5 Cool, remove the test pieces from the solution and rinse with distilled water, collecting the rinsings in the same beaker as the solution. NOTEThe amount of copper in the stripping solut

32、ion may be relatively high because some of the tin is present in the coating as copper-tin compounds and these have to be removed to obtain the total tin in the coating. 7.2.6 Dry and weigh the test pieces and calculate the approximate mass of tin coating removed. This mass is not sufficiently accur

33、ate for the calculation of the percentage of lead because of the dissolution of trace amounts of the substrate, but provides guidance to ensure that approximately0.1g of tin coating has been obtained. 7.2.7 Add5mL of nitric acid solution(4.8) to the solution, transfer to a50mL volumetric flask and m

34、ake up to the mark with water. Use this solution to determine lead as described in7.4. 7.2.8 Transfer10.0mL of the solution(see7.2.7) to a50mL volumetric flask, add16mL of copper sulphate solution(4.9),4mL of nitric acid solution(4.8) and make up to the mark with water. Use this solution to determin

35、e tin as described in7.4. 7.2.9 Repeat the test procedure omitting the test pieces to provide a blank determination. 7.3 Calibration for tin and lead 7.3.1 Prepare a calibration curve as described in7.3.2 to7.3.4; alternatively, any method of calibration shown to be of equivalent accuracy and precis

36、ion may be used.BS6534:1984 BSI 12-1999 3 7.3.2 Measure the following amounts of solution into50mL volumetric flasks using a burette or suitable pipettes(5.4): 0,0.5,1.0,2.0 and4.0mL of tin solution 1mL=10mg Sn(4.11.2) 0,0.5,1.0,2.0 and4.0mL of lead solution 1mL=0.1mg Pb4.11.3 a) Add20mL of copper s

37、ulphate solution(4.9),5mL of nitric acid solution(4.8) and make up to the mark with water. 7.3.3 Aspirate these standard solutions into the flame using the appropriate conditions(5.2) and determine the absorbance of each solution. 7.3.4 Deduct the blank value and prepare a calibration curve for each

38、 metal by plotting absorbance against mass (in mg) of metal. Use these curves to determine the mass of lead and tin (in mg) in the test solutions. 7.4 Determination of tin and lead in the test solutions 7.4.1 Aspirate the test solution obtained in either7.1.8 or7.2.7 (lead) and7.1.9 or7.2.8 (tin) in

39、to the flame using the appropriate conditions(5.2) and determine the absorbance of each solution. 7.4.2 Deduct the blank value and determine the mass of lead and tin (in mg) in the test solution by reference to the calibration curves(see7.3.4). If the lead content of a solution under examination is

40、below the first standard on the curve, proceed as in7.5. 7.5 Concentration step for determination of low amounts of lead 7.5.1 Transfer a25.0mL aliquot of the test solution obtained in either7.1.8 or7.2.7 to a100mL beaker and evaporate just to dryness on a water bath. 7.5.2 Cool, add2mL of the acid

41、mixture(4.10), warm to dissolve, cool, transfer to a10mL volumetric flask and make up to the mark with water. 7.5.3 Determine the lead as described in7.4 using a new calibration curve, prepared for low amounts of lead, according to7.6. 7.6 Calibration for low amounts of lead 7.6.1 Prepare a calibrat

42、ion curve as described in7.6.2 to7.6.5; alternatively, any method of calibration shown to be of equivalent accuracy and precision may be used. 7.6.2 Measure the following amounts of solution into100mL beakers using a burette or suitable pipettes(5.4): 0,1.0,2.0,4.0 and6.0mL of lead solution 1mL=0.01

43、mg Pb4.11.3 b) Add10mL of copper sulphate solution(4.9) to each beaker and evaporate just to dryness on a water bath. 7.6.3 Cool, add2mL of the acid mixture(4.10), warm to dissolve, cool, transfer to a10mL volumetric flask and make up to the mark with water. 7.6.4 Aspirate these standard solutions i

44、nto the flame using the appropriate conditions(5.2) and determine the absorbance of each solution. 7.6.5 Deduct the blank value and prepare a calibration curve by plotting absorbance against mass (in mg) of lead. Use this curve to determine the mass of lead (in mg) in the concentrated test solution

45、obtained in7.5.2. 8 Expression of results and reproducibility of the method 8.1 The lead content of the coating is expressed as a percentage by mass of the tin, calculated according to8.1.1 and8.1.2. 8.1.1 For determinations without a concentration step: 8.1.2 For determinations using a concentratio

46、n step: 8.2 The method is capable of a reproducibility of 10% at the0.2% Pb level. 8.3 The coating stripped from the article will consist of tin plus any intermetallic compounds of tin with the substrate metal(s). For this reason the analysis of a coating may not accord precisely with that of the ti

47、n used to provide the coating. 9 Test report The test report shall include the following: a) the type of article under test; b) identification of the substrate metal; c) the number of test pieces taken from the article; d) the position(s) within the article from which the test pieces were taken; e)

48、the amount of lead in the tin coating expressed as a percentage of the tin extracted; % Pb mass of Pb (mg) in the test solution from 7.1.8 or 7.2.7 5mass of Sn (mg) in the test solution from 7.1.9 or 7.2.8 - =100 % Pb 2mass of Pb (mg) in the concentrated solution from 7.5.2 mass of Sn (mg) in the te

49、st solution from 7.1.9 or 7.2.8 -100 =BS6534:1984 4 BSI 12-1999 f) whether or not a concentration step(see 7.5) was used; g) reference to this BritishStandard, i.e.BS6534.BS6534:1984 BSI 12-1999 Publications referred to BS700, Graduated pipettes. BS846, Specification for burettes. BS1792, Specification for one-mark volumetric flasks. BS3788, Specification for tin coated finish on culinary utens