1、BRITISH STANDARD BS 6783-6: 1986 ISO 7525: 1985 Sampling and analysis of nickel, ferronickel and nickel alloys Part 6: Method for determination of sulphur in nickel by methylene blue molecular absorption spectrometry after generation of hydrogen sulphide ISO title: Nickel Determination of sulfur con
2、tent Methylene blue molecular absorption spectrometric method after generation of hydrogen sulfide UDC 669.24 + 669.1524-198:546.22:543.422.062BS6783-6:1986 This British Standard, having been prepared under the directionof the Non-ferrous Metals Standards Committee, waspublished under the authorityo
3、f the Board of BSI andcomes intoeffect on 31 December 1986 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference NFM/10 Draft for comment 84/39888 DC ISBN 0 580 15525 0 Committees responsible for this British Standard The preparation of this British Standa
4、rd was entrusted by the Non-ferrous Metals Standards Committee (NFM/-) to Technical Committee NFM/10, upon which the following bodies were represented: British Non-ferrous Metals Federation British Steel Industry Engineering Equipment and Materials Users Association Ministry of Defence Process Plant
5、 Association Stainless Steel Fabricators Association of Great Britain Coopted members Amendments issued since publication Amd. No. Date of issue CommentsBS6783-6:1986 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope and field of application 1 2 Refer
6、ence 1 3 Principle 1 4 Reagents and materials 1 5 Apparatus 2 6 Sampling and samples 2 7 Procedure 2 8 Expression of results 3 9 Notes on procedure 3 10 Test report 4 Figure 1 Apparatus for purification of acids 4 Figure 2 Apparatus for purification of the reducing mixture 5 Figure 3 Apparatus for d
7、istillation of hydrogen sulfide 6 Table 3 Publications referred to Inside back coverBS6783-6:1986 ii BSI 10-1999 National foreword This Part of BS 6783 has been prepared under the direction of the Non-ferrous Metals Standards Committee. It is identical with ISO 7525:1985 “Nickel Determination of sul
8、fur content Methylene blue molecular absorption spectrometric method after generation of hydrogen sulfide” published by the International Organization for Standardization (ISO). At present this British Standard consists of nine Parts all concerned with analysis of nickel, ferronickel and nickel allo
9、ys. Further International Standards are in preparation on sampling and analysis of nickel, ferronickel and nickel alloys and, when available, these will be published as further Parts of this British Standard. Terminology and conventions. The text of the International Standard has been approved as su
10、itable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to
11、 use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Part of BS 6783”. In British Standards it is current practice to use the symbol “L” for litre (and in its submultiples) rather than “l” and
12、 to use the spelling “sulphur”, etc., instead of sulfur, etc. 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 Standard does not of itself confer immunity fro
13、m legal obligations. Cross-references International Standards Corresponding British Standards ISO 5725:1981 BS 5497 Precision of test methods Part 1:1979 Guide for the determination of repeatability and reproducibility for a standard test method (Technically equivalent) ISO 7526:1986 BS 6783 Samplin
14、g and analysis of nickel, ferronickel and nickel alloys Part 7:1986 Method for determination of sulphur in nickel, ferronickel and nickel alloys by infra-red absorption after induction furnace combustion (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages
15、 i and ii, pages1 to 6, 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.BS6783-6:1986 BSI 10-1999 1 1 Scope and field of application This Inter
16、national Standard specifies a molecular absorption spectrometric method after generation of hydrogen sulfide for the determination of the sulfur content of refined nickel in the range 0,000 1 to0,002% (m/m). 2 Reference ISO 5725, Precision of test methods Determination of repeatability and reproduci
17、bility by inter-laboratory tests. 3 Principle Dissolution of a test portion in a nitric acid-chloric acid mixture and oxidation of total sulfur to sulfate ion. Removal of nitrates by evaporation with hydrochloric and formic acids. Reduction of sulfate to hydrogen sulfide by hydroiodic and hypophosph
18、orous acids in an argon atmosphere. Absorption of the hydrogen sulfide by a zinc amminecomplex solution. Conversion of absorbed sulfide sulfur to methylene blue and measurement of absorbance of the solution at 665 nm. Determination of the mass of sulfur from a calibration graph. 4 Reagents and mater
19、ials During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. All acids used in the dissolution of the test portion and the nitrate removal step shall be purified by distillation to eliminate sulfur-contain
20、ing species, such as sulfur dioxide and sulfuric acid. Impurity levels of 1 mg of sulfur per litre are not sufficiently low. To keep the blank test sulfur content low, hydrochloric acid, in particular, should contain less than 0,05 mg of sulfur per litre. 4.1 Hydrochloric acid, 20= 1,18 g/ml, dilute
21、d 1 + 4. 4.2 Purified hydrochloric acid, 20= 1,098 g/ml. Distil hydrochloric acid ( 20= 1,18 g/ml) diluted 3 + 2 with water using the apparatus shown in Figure 1 and discard the first 10% (V/V) of the distillate. Collect the remaining distillate (except for the last few millilitres) in a thoroughly
22、cleaned glass bottle. 4.3 Purified formic acid, 20= 1,20 g/ml. Distil formic acid using the apparatus shown in Figure 1 and discard the first 10% (V/V) of the distillate. Collect the remaining distillate (except for the last few millilitres) in a thoroughly cleaned glass bottle. 4.4 Nitric acid-chlo
23、ric acid mixture 4.4.1 Distil nitric acid ( 20= 1,41 g/ml) using the apparatus shown in Figure 1 and discard the first10% (V/V) of the distillate. Collect the remaining distillate (except for the last few millilitres) in a thoroughly cleaned brown glass bottle. 4.4.2 Dissolve 3 g of potassium chlora
24、te (KClO 3 ) in30 ml of water and add 100 ml of purified nitric acid (4.4.1). Prepare fresh as needed. 4.5 Zinc acetate, absorbing solution. Dissolve 5 g of zinc acetate dihydrate Zn(CH 3 COO) 2 2H 2 O and 70 g of ammonium chloride (NH 4 Cl) in about 350 ml of water. Add 7,5g of sodium hydroxide (Na
25、OH), stir to dissolve, and dilute to 500 ml with water. Store in a glass bottle. 4.6 Reducing mixture Transfer 420 ml of hydroiodic acid 20= 1,7 g/ml, 55% (m/m) HI minimum, 80 ml of hypophosphorous acid 20= 1,21 g/ml, 50% (m/m) H 3 PO 2minimum and 70 g of sodium iodide to the purifying apparatus (se
26、e Figure 2). Attach the hydrogen sulfide trap containing 50 ml of the absorbing solution (4.5). Purge with argon at a flow rate of 200 to 300 ml/min for 10 min to expel air from the system. Switch on the electric heating mantle and heat the mixture at 113 to 115 C for 4 h in a continuous flow of arg
27、on. Allow the mixture to cool while maintaining the argon flow. Transfer the cold reducing mixture, without delay, to a brown glass bottle. Stopper and store in a cool dark place. (See clause 9.) 4.7 Diamine salt, solution. Dissolve 0,1 g of N, N-dimethyl-p-phenylenediamine hydrochloride or sulfate
28、in 26 ml of hydrochloric acid ( 20= 1,18 g/ml) and dilute to 100 ml with water. Store in a cool dark place. Prepare fresh weekly. 4.8 Iron(III) chloride, solution. Dissolve 1,0 g of iron(III) chloride hexahydrate (FeCl 3 6H 2 O) in 10 ml of hydrochloric acid ( 20= 1,18 g/ml) and 40 ml of water. Dilu
29、te to100 ml with water. Store in a glass bottle. 4.9 Sulfur, standard solution, corresponding to100mg of S per litre. Dissolve exactly 0,543 5 g of potassium sulfate, previously dried at 105 C for 1 h, in water in a1000ml one-mark volumetric flask. Make up to the mark with water and mix.BS6783-6:198
30、6 2 BSI 10-1999 1 ml of this standard solution contains 0,100 mg ofS. 4.10 Argon 99,998% (m/m) Ar minimum. 5 Apparatus Ordinary laboratory glassware, and 5.1 Distillation apparatus, for the generation and volatilization of hydrogen sulfide from the test solution, as shown in Figure 3. The double sur
31、face condenser is preferred because of its superior cooling efficiency. 5.2 Heating mantle. The optimum temperature for a rapid reduction of sulfate to hydrogen sulfide is around 114 C. The solution would then reflux very gently. The required power setting for the mantle shall be established by prel
32、iminary blank tests with a thermometer dipped in the heated solution. 5.3 Molecular absorption spectrometer, suitable for measuring absorbance at 665 nm. 5.4 Micropipettes, of capacities 10; 20; 50; and1004l. 6 Sampling and samples 6.1 Sampling and preparation of the laboratory sample shall be carri
33、ed out by normal agreed procedures or, in case of dispute, by the relevant International Standard. 6.2 The laboratory sample normally is in the form of a powder, granules, millings or drillings and no further preparation of the sample is necessary. 6.3 If it is suspected that the laboratory sample i
34、s contaminated with oil or grease from the milling or drilling process, it shall be cleaned by washing with high purity acetone and drying in air. 6.4 If the laboratory sample contains particles or pieces of widely varying sizes, the test portion should be obtained by riffling. 7 Procedure WARNING T
35、here are toxicity risks related to the chemicals used in the procedure and reasonable precautions shall be taken. The glassware used in the distillation apparatus shall be examined carefully and its performance and tightness of joints checked. 7.1 Test portion and preparation of test solution 7.1.1
36、Weigh, to the nearest 0,01 g, 1,0 g of the test sample and transfer to a 100 or 250 ml three neck round bottom flask. Add 10 ml of nitric acid-chloric acid mixture (4.4) and allow the reaction to subside. Carefully evaporate the solution to a viscous syrup. 7.1.2 Add 10 ml of purified hydrochloric a
37、cid (4.2) and heat to dissolve the residue. Add 2 ml of formic acid(4.3) and evaporate to dryness. Dissolve the dryresidue in 10 ml of purified hydrochloric acid and0,5ml of formic acid. Heat and mineralize for a few minutes on the hotplate to complete dissolution and cool. NOTE 1It is essential tha
38、t all sample treatment be carried out in a scrupulously clean laboratory atmosphere, i.e. free from sulfuric acid fumes and any vapours or dust containing sulfur species. Dissolution of the test portion in the three neck flask, rather than a beaker, reduces the chance of contamination. NOTE 2The thr
39、ee neck flask may be held in a cylindrical metal holder for heating on a hotplate. A sand-bath on a hotplate may also be used. Alternatively the flask may be suspended in a low-form beaker of suitable size. NOTE 3If brown fumes appear during the final dissolution, evaporate to dryness again and diss
40、olve the residue in hydrochloric and formic acids as indicated in 7.1.2. 7.2 Hydrogen sulfide evolution 7.2.1 Attach the three neck flask to the distillation apparatus (5.1). Place 3 ml of hydrochloric acid diluted 1 + 4 into the acid trap, and 5,0 ml of absorbing solution (4.5) into the hydrogen su
41、lfide trap. Add 30 ml of the reducing mixture (4.6) to the sample solution via the side arm. Replace the stopper. 7.2.2 Ensure that all joints are secure and pass a flow of argon (4.10) through the apparatus at a rate of 30 ml/min. After approximately 2 min switch on the heating mantle and continue
42、heating for 30 min. Remove the sulfide trap and switch off the heating mantle. 7.3 Methylene blue development 7.3.1 Introduce 3,0 ml of the diamine salt solution(4.7) into the sulfide trap via the gas inlet tube. Immediately follow with addition of 0,5 ml of iron(III) chloride solution (4.8) and mix
43、 gently. 7.3.2 Rinse the inside and outside of the gas inlet tube with a small quantity of water. Mix the solution and transfer it to a 25 ml one-mark volumetric flask. Wash the test-tube with water. Make up to the mark with water, mix, and allow the solution to stand for at least 30 min before meas
44、urement. NOTEOnce fully developed, the methylene blue coloration is stable for at least 24 h. 7.4 Spectrometric measurement Measure the absorbance of the solution using 1 or 2 cm cells against water as the reference at a wavelength of 665 nm with the molecular absorption spectrometer (5.3).BS6783-6:
45、1986 BSI 10-1999 3 7.5 Blank test 7.5.1 Carry out a blank test in the same apparatus, by the same procedure, using the same quantities of all the reagents as in the determination, but omitting the test portion. 7.5.2 Having finished the volatilization of hydrogen sulfide from the blank test as in 7.
46、2.2, allow the now sulfur-free reducing solution to cool in a flow of argon and use it in the calibration (7.6). 7.6 Calibration 7.6.1 To the cold ( 50 C) sulfur-free reducing mixture (7.5.2) in the three neck flask add, from a micropipette, 10 4l (1 4g S) of sulfur standard solution (4.9). Proceed
47、as directed in 7.2 to 7.4. 7.6.2 Continue with additions, in order of 20; 50; and 100 4l (2; 5; and 10 4g S) of sulfur standard solution (4.9), to the same cold sulfur-free reducing mixture as in 7.6.1. 7.6.3 Plot the absorbance readings of solutions obtained in 7.6.1 and 7.6.2 against the mass, in
48、micrograms, of sulfur present in the solutions. The graph does not have to pass through the origin as the absorbing solution (4.5) usually shows a slight background absorption upon addition of the diamine salt and iron(III) chloride. 8 Expression of results 8.1 Calculation The sulfur content, expres
49、sed as a percentage by mass, of the test portion, is given by the formula where For a meaningful result, the following condition shall apply: m 1W 2m 2 . If m1 2m 2 , the reagent blank shall be improved by additional purification of the reagents used. Another possible source for high blanks can be the laboratory environment. NOTEA blank value of 0,5 4g sulfur has been found attainable and acceptable. 8.2 Precision This International Standard was subjected to a limited inter-laboratory test programme involving only three labor
