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1、BRITISH STANDARD BS 6200-3.16.3: 1991 Sampling and analysis of iron, steel and other ferrous metals Part 3: Methods of analysis Section 3.16 Determination of lead Subsection 3.16.3 Steel: spectrophotometric method for trace amounts Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:03:18 GMT+
2、00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.16.3:1991 This British Standard, having been prepared under the direction of the Iron and Steel Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 29 November 1991 BSI 09-1999 The following BS
3、I references relate to the work on this standard: Committee reference ISM/18 Draft for comment 91/35214 DC ISBN 0 580 19945 2 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Iron and Steel Standards Policy Committee (ISM/-) to Technical
4、Committee ISM/18, upon which the following bodies were represented: BCIRA British Steel Industry Department of Trade and Industry (Laboratory of the Government Chemist) Ferro Alloys and Metals Producers Association Ministry of Defence Amendments issued since publication Amd. No.DateComments Licensed
5、 Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:03:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.16.3:1991 BSI 09-1999i Contents Page Committees responsibleInside front cover Forewordii 1Scope1 2Principle1 3Reagents1 4Apparatus1 5Sampling1 6Procedure2 7Calculation and expression of resul
6、ts3 8Test report4 Table 1 Precision data4 Table 2 Predicted valves of r and R4 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:03:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.16.3:1991 ii BSI 09-1999 Foreword This Subsection of BS 6200 h
7、as been prepared under the direction of the Iron and Steel Standards Policy Committee and supersedes method 3 for the determination of lead in BSI Handbook No. 19, to which it is technically equivalent. BS 6200 is a multipart British Standard, covering all aspects of the sampling and analysis of iro
8、n, steel and other ferrous metals. A list of contents, together with general information, is given in Part 1. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British
9、 Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments inc
10、orporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:03:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.16.3:1991 BSI 09-19991 1 Scope This Subsection of BS 6200 describes a spectrophotometric method for
11、 the determination of trace amounts of lead in steel. The method is applicable to lead contents from 0.0005 % (m/m) to 0.05 % (m/m). NOTEThe titles of publications referred to in this Subsection of BS 6200 are listed on the inside back cover. 2 Principle From an oxidized hydrochloric acid solution o
12、f the steel, iron is removed by extraction into amyl acetate. Lead is extracted into chloroform as its diethyldithiocarbamate complex from a citrate-cyanide solution. The lead complex is selectively extracted in hydrochloric acid solution to separate it from bismuth. It is then converted to its dith
13、izone complex in ammoniacal citrate-cyanide solution and extracted in chloroform. The determination is completed spectrophotometrically. 3 Reagents NOTEWhere available lead-free reagents should be used. During the analysis use only reagents of recognized analytical grade and which are known to give
14、a very low lead blank. Use only grade 3 water as specified in BS 3978. 3.1 Ammonia solution, density = 0.91 g/mL. 3.2 Ammonia solution, = 0.91 g/mL, diluted 1 + 1. 3.3 Ammonia solution, = 0.91 g/mL, diluted 1 + 3. 3.4 Ammonium citrate. Dissolve 25 g of citric acid, H8C6O7H2O, in the minimum amount o
15、f water. Neutralize with ammonia solution (3.1), dilute to 100 mL and mix. 3.5 Amyl acetate NOTEThis solvent is NOT pentyl acetate, (n-amyl acetate), but consists principally of 3-methylbutyl acetate with a small proportion of 2-methylbutyl acetate. 3.6 Chloroform 3.7 Citric acid, 250 g/L solution.
16、Dissolve 25 g of citric acid, H8C6O7.H2O), in water, dilute to 100 mL and mix. 3.8 Dithizone, 0.05 g/L solution. Dissolve 0.005 g of dithizone in chloroform, dilute to 100 mL with chloroform and mix. 3.9 Hydrochloric acid, = 1.16 g/mL to 1.18 g/mL. 3.10 Hydrochloric acid, = 1.16 g/mL to 1.18 g/mL, d
17、iluted 1 + 19. 3.11 Hydroxylammonium chloride, 10 g/L solution. Dissolve 1 g of hydroxylammonium chloride in water, dilute to 100 mL and mix. 3.12 Lead, standard solution, 0.01 mg lead per millilitre. Wash approximately 1 g of lead, of purity at least 99.9 % (m/m), in boiling hydrochloric acid (3.9)
18、 diluted 1 + 7 (V/V). Wash with water, rinse in acetone and dry in a vacuum desiccator. Weigh, to the nearest 0.001 g, 0.5 g of the clean lead and dissolve in 20 mL of nitric acid (3.14). Boil to remove nitrous fumes, and cool. Transfer to a 1 L volumetric flask, dilute to the mark and mix. Transfer
19、 20 mL of this lead solution (0.5 mg of lead per millilitre) by means of a pipette to a 1 L volumetric flask and mix. 3.13 Nitric acid, = 1.42 g/mL. 3.14 Nitric acid, = 1.42 g/mL, diluted 1 + 4. 3.15 Perchloric acid, = 1.54 g/mL. 3.16 Potassium cyanide, 100 g/L solution. Dissolve 25 g of potassium c
20、yanide in water, dilute to 250 mL, and mix. 3.17 Potassium cyanide, 5 g/L solution. Dissolve 2.5 g of potassium cyanide in water, dilute to 500 mL, and mix. 3.18 Sodium diethyldithiocarbamate, 2 g/L solution. Dissolve 0.2 g sodium diethyldithiocarbamate in water, dilute to 100 mL and mix. 3.19 Sodiu
21、m hydroxide, 2 g/L solution. Dissolve 0.2 g of sodium hydroxide in water, dilute to 100 mL and mix. Prepare and store this solution in a polyethylene container. 3.20 Sulfuric acid, = 1.84 g/mL, diluted 1 + 1. To 100 mL of water add cautiously 125 mL of sulfuric acid = 1.84 g/mL, stirring constantly.
22、 Cool, dilute to 250 mL and mix. 3.21 Thymol blue, 0.4 g/L solution. Dissolve 0.1 g of thymol blue by warming with 4 mL of sodium hydroxide solution (3.19) and 5 mL of ethanol. Add 50 mL of ethanol, dilute to 250 mL with water and mix. 4 Apparatus 4.1 Ordinary laboratory apparatus 4.2 Volumetric gla
23、ssware, in accordance with class A of BS 846, BS 1583 or BS 1792, as appropriate. 4.3 Spectrophotometer 4.4 Cells, having an optical path length of 1 cm. 5 Sampling Carry out sampling in accordance with BS 1837. NOTEBS 6200-2, which will supersede BS 1837, is currently in preparation. On its publica
24、tion, this Subsection will be amended to include sampling in accordance with BS 6200-2. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:03:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.16.3:1991 2 BSI 09-1999 6 Procedure 6.1 Test portion Weigh, to the nearest 0.001 g, a test port
25、ion of 0.5 g. 6.2 Blank test In parallel with the determination and following the same procedure, carry out a blank test using the same quantities of all reagents. NOTEA typical blank value for this method in the range 0.0005 % (m/m) to 0.010 % (m/m) lead is equivalent to approximately 0.0005 % (m/m
26、) lead. 6.3 Determination 6.3.1 Preparation of the test solution 6.3.1.1 Place the test portion in a 250 mL conical beaker. Add 5 mL of hydrochloric acid (3.9) and 1 mL of nitric acid (3.13), and heat gently until solvent action ceases. Add 0.5 mL of perchloric acid (3.15), evaporate to dryness and
27、bake for 10 min. For samples containing niobium or titanium use 8 mL of sulfuric acid (3.20) instead of the perchloric acid, evaporate until slight fumes of sulfur trioxide appear, and cool. NOTEThese and all subsequent reagent additions should be made by means of a safety pipette or burette. 6.3.1.
28、2 Redissolve the residue in 10 mL of hydrochloric acid (3.9), cool and transfer to a 150 mL separating funnel. Rinse the beaker three times with 3 mL portions of hydrochloric acid (3.9) and combine with the solution in the separating funnel. Add 25 mL of amyl acetate (3.5) and shake vigorously for 2
29、 min. Allow the layers to separate and run off the lower (acid) layer into a 250 mL conical beaker. Wash the amyl acetate layer twice by shaking with 2 mL portions of hydrochloric acid (3.9), allowing the layers to separate, and combining the acid layers with the first acid extract. 6.3.2 Removal of
30、 bismuth NOTEFor unalloyed and low-alloy steels where bismuth is known to be absent the directions given in 6.3.2 may be omitted. Add 0.5 mL of perchloric acid (3.15) and a few drops of nitric acid (3.13) to the acid extract, cover the beaker and evaporate until fumes appear. Cool, add 2 mL of hydro
31、chloric acid (3.9) and 10 mL of hydroxylammonium chloride solution (3.11). Warm to redissolve any salts, then boil for 2 min. Add 20 mL of ammonium citrate solution (3.4), heat to incipient boiling and simmer for 3 min. Cool, neutralize with ammonia solution (3.2) to pH 7.5 to pH 9.0, testing the so
32、lution with a narrow-range pH testpaper, then transfer to a 200 mL separating funnel marked at 100 mL and dilute to the mark. Add 20 mL of potassium cyanide solution (3.16). For samples containing more than 30 % (m/m) of nickel add an extra 5 mL of potassium cyanide solution (3.16) for every additio
33、nal 10 % of nickel. Add 10 mL of sodium diethyldithiocarbamate solution (3.18), mix and allow to stand for 2 min. Extract the lead complex three times by shaking with successive additions of 15 mL, 10 mL, and 10 mL of chloroform (3.6), each time allowing the layers to separate and combining the chlo
34、roform extracts in a 250 mL conical beaker. Transfer the combined chloroform extracts to a 100 mL separating funnel and shake with 25 mL of hydrochloric acid (3.10). Allow the layers to separate and run off the lower (chloroform) layer into a second 100 mL separating funnel. Repeat the extraction fr
35、om the chloroform by shaking with a second portion of 25 mL of hydrochloric acid (3.10). Allow the layers to separate, run off and discard the lower (chloroform) layer. Combine the two aqueous layers in a 250 mL conical beaker. 6.3.3 Treatment of the lead solution Add 1 mL of nitric acid (3.13), 2 m
36、L of perchloric acid (3.15) and 4 mL of sulfuric acid (3.20), cover the beaker, then evaporate to fumes of sulfur trioxide. Cool, add 10 mL of hydroxylammonium chloride solution (3.11) and 2.5 mL of hydrochloric acid (3.9), heat gently for 5 min and cool. Rinse the cover and walls of the beaker with
37、 5 mL of water, add 1 mL of citric acid solution (3.7), three drops of thymol blue indicator (3.21), then add ammonia solution (3.1) until the colour of the indicator changes to blue. Add 5 mL of ammonia solution (3.2) and cool. If the sample contains more than 0.01 % (m/m) lead, dilute the solution
38、 to 50 mL in a volumetric flask and take a suitable aliquot for the test. It is essential that the blank test is fractionated in the same way. 6.3.4 Development of the colour Transfer the solution or aliquot to a 150 mL separating funnel marked at 50 mL and rinse with water. Add 5 mL of potassium cy
39、anide solution (3.16) and dilute to the mark. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 15:03:18 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.16.3:1991 BSI 09-19993 From a burette, add 8.0 mL of chloroform (3.6) and then add dithizone solution (3.8) (also from a burette) 1.0 mL
40、at a time, shaking between each addition, until an excess of dithizone is indicated by the colour of the chloroform layer changing to a purple-blue. Add 2.0 mL of dithizone solution (3.8) in excess, then sufficient chloroform (3.6) to bring the total amount of chloroform and dithizone solution to 15
41、.0 mL. Shake vigorously for 2 min, allow the two layers to separate, then run the chloroform layer into another separating funnel containing 40 mL of potassium cyanide solution (3.17) and 10 mL of ammonia solution (3.3). Shake for 1 min and allow the layers to separate. Filter the chloroform layer t
42、hrough a 5.5 cm rapid filter paper into a clean dry 1 cm cell, discarding the initial few drops. 6.3.5 Spectrophotometric measurement Set the spectrophotometer (4.3) to zero absorbance in relation to water. Measure the absorbance of the test solution and the blank at a wavelength of 510 nm. Convert
43、the readings obtained to milligrams of lead by reference to the calibration graph (6.4). 6.4 Establishment of the calibration graph To a series of six 250 mL conical beakers, add 0.0 mL, 1.0 mL, 2.0 mL, 3.0 mL, 4.0 mL, and 5.0 mL of lead solution (3.12). Add 5 mL of hydrochloric acid (3.9) and 1 mL
44、of nitric acid (3.13). Add 5 mL of perchloric acid (3.15) and evaporate the solutions to dryness. Continue by following the procedure given in 6.3.1.2 to 6.3.5, and prepare a calibration graph by plotting the absorbance readings obtained against the equivalent milligrams of lead. 7 Calculation and e
45、xpression of results 7.1 Calculation Calculate the lead content, expressed as percentage by mass, from the equation: where If an aliquot of volume V (in mL) was taken from 50 mL in 6.3.3, multiply the lead content calculated from the equation by the factor F, where F = 50/V. 7.2 Precision 7.2.1 Prec
46、ision data A planned trial of this method was carried out by five analysts, each from a different laboratory; six tests were carried out by each analyst on each of six samples. From the results obtained, the 95 % confidence limits (2s) have been calculated in accordance with BS 5497-1 and are given
47、in Table 1. The difference between two single results found on identical material by one analyst using the same apparatus within a short time interval will exceed the repeatability r not more than once in 20 cases, on average, in the normal and correct operation of the method. The difference between
48、 two single and independent results found by two operators working in different laboratories on identical test material will exceed the reproducibility R on average, not more than once in 20 cases in the normal and correct operation of the method. 7.2.2 Regression data Statistical analysis of the re
49、sults shows a logarithmic relationship between lead content and the values of repeatability, r, and reproducibility, R, summarized by the following logarithmic equations: log r = 0.5385 log Pb 2.0810 correlation coefficient = 0.990 log R = 0.4642 log Pb 2.0817 correlation coefficient = 0.940 with concentration of lead content Pb, r and R expressed as % (m/m). lead content m1m0 10 m - -= m1is the mass of lead found in the test solution (in mg); m0is the mass of lead found in the blank solution (6.2) (in mg); mis the mass of
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