1、BRITISH STANDARD CONFIRMED AUGUST 1993 BS 6392-6: 1983 Incorporating Amendment No.1 Testing of ethanol for industrial use Part6: Method for determination ofmethanol content0.01% (V/V) to0.20% (V/V) (photometric method) NOTEIt is recommended that this Part be read in conjunction with the information
2、given in the “General introduction” published separately asBS6392-0. UDC 661.722:543.42.062:547.261BS6392-6:1983 This British Standard, having been prepared under the directionof the Chemicals Standards Committee, was published under the authority ofthe Board of BSI and comesintoeffect on 31August19
3、83 BSI 12-1999 The Committees responsible for this British Standard are shown inPart0. The following BSI references relate to the work on this standard: Committee reference CIC/4 Draft for comment80/51209 DC ISBN 0 580 13372 9 Foreword This Part ofBS6392 is technically equivalent toISO1388 “Ethanol
4、for industrial use Methods of test” Part7 “Determination of methanol content methanol contents between0,01 and0,20% (V/V) Photometric method”, published in1981 by the International Organization for Standardization (ISO). For ease of production, the text ofISO1388-7:1981, with the omission of the Ann
5、ex, has been used for this British Standard. 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 use a full point o
6、n the baseline as the decimal marker. In3.3.2 reference is made to a sintered glass filter funnel grade number4A complying withBS1752. WhenBS1752 is revised it is expected that it will be identical withISO4793 in which the equivalent to grade4A ofBS1752:1963 is porosity gradeP10. This standard descr
7、ibes a method only and should not be used as a specification defining limits of purity. Reference to the standard should indicate that the method of test used is in accordance withBS6392-6. A British Standard does not purport to include all the necessary provisions of a contract. Users of British St
8、andards 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 and2, an inside back cover and a back cover. This s
9、tandard 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. Amendments issued since publication Amd. No. Date of issue Comments 4942 March 1986 Indicated by a sideline in the marginBS6392-6:1983 BSI
10、12-1999 i Contents Page Foreword Inside front cover 1 Scope and field of application 1 2 Principle 1 3 Reagents 1 4 Apparatus 1 5 Procedure 1 6 Expression of results 2 Publications referred to Inside back coverii blankBS6392-6:1983 BSI 12-1999 1 1 Scope and field of application This Part ofBS6392 de
11、scribes a photometric method for the determination of the methanol content of ethanol for industrial use. The method is applicable to products having methanol contents between0,01 and0,20% (V/V). NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 P
12、rinciple Conversion of the methanol present in a test portion to formaldehyde by oxidation with a solution of potassium permanganate in phosphoric acid. Reaction of the formaldehyde formed with chromotropic acid. Photometric measurement of the violet coloration obtained at a wavelength of about570nm
13、. 3 Reagents During the analysis, use only reagents of recognized analytical grade, and distilled water or water of equivalent purity. 3.1 Potassium permanganate,30g/l solution in phosphoric acid. Dissolve3g of potassium permanganate in a little water, add15,5ml of orthophosphoric acid solution, 1,6
14、9g/ml, dilute to100ml with water and mix. 3.2 Disodium disulphite sodium metabisulphite (Na 2 S 2 O 5 ),100g/l solution. Dissolve10g of sodium metabisulphite in water and dilute to100ml. 3.3 4,5-Dihydroxynaphthalene-2,7-disulphonic acid (chromotropic acid), solution in sulphuric acid. 3.3.1 Preparat
15、ion of the solution Dissolve0,1g of chromotropic acid, or its disodium salt, in10ml of water. Add, while cooling,90ml of sulphuric acid, approximately1,81g/ml, about90% (m/m) solution, and mix. Prepare this solution at the time of use. If the solution causes significant coloration during colour deve
16、lopment of the compensation solution(5.3.1) or the blank test solution(5.2), purify the chromotropic acid, or its disodium salt, in accordance with the procedure specified in3.3.2. 3.3.2 Purification of the chromotropic acid Dissolve about10g of chromotropic acid, or its disodium salt, in25ml of wat
17、er. If the disodium saltis used, add, while cooling,2ml of sulphuric acid, approximately1,84g/ml, to convert it to the free acid. Add50ml of methanol, heat just to boiling and filter through a sintered glass filter funnel, grade number4A complying withBS1752. Add100ml of propan-2-ol to the solution
18、to precipitate the chromotropic acid. Collect the precipitate on a sintered glass filter funnel, grade number4A complying withBS1752 and wash it with small portions of propan-2-ol. Allow to dry, initially in air, and finally in a desiccator over sulphuric acid, approximately1,84g/ml, about98%(m/m) s
19、olution, as desiccant. If, after purification, the blank test solution is still coloured, reject the chromotropic acid. 3.4 Methanol, standard solution corresponding to0,05% (V/V) of methanol. Place1,00ml of absolute methanol in a250ml one-mark volumetric flask, add a quantity of methanol-free ethan
20、ol corresponding to99ml of anhydrous ethanol, dilute to the mark with water and mix. Place25,0ml of this solution in a200ml one-mark volumetric flask, dilute to the mark with water and mix. 1ml of this standard solution contains0,0005ml of methanol. NOTEIndustrial methylated spirits95% (V/V) is not
21、suitable for use in place of the methanol-free ethanol used in the preparation of this reagent. 4 Apparatus Ordinary laboratory apparatus, and 4.1 Water bath, capable of being controlled at70 2 C. 4.2 Spectrophotometer, or 4.3 Photoelectric absorptiometer, fitted with filters ensuring maximum transm
22、ission in the region of570nm. 5 Procedure NOTEIndustrial methylated spirits95% (V/V) is not suitable for use in place of the ethanol specified in5.2, 5.3.1, 5.3.4 and5.4.2. 5.1 Test portion and preparation of the test solution Take as the test portion a volume (V 2 ) of the laboratory sample corresp
23、onding to5,0ml of anhydrous ethanol and place it in a100ml one-mark volumetric flask. Prepare the test solution by diluting to the mark with water and mixing. 5.2 Blank test Carry out a blank test at the same time as the determination, following the same procedure and using the same quantities of al
24、l the reagents used for the determination, but replacing the test portion by a volume of methanol-free ethanol corresponding to5,0ml of anhydrous ethanol.BS6392-6:1983 2 BSI 12-1999 5.3 Preparation of the calibration graph 5.3.1 Preparation of standard solutions, used for the preparation of standard
25、 colorimetric solutions Into a series of six100ml one-mark volumetric flasks, place the volumes of the standard methanol solution(3.4) indicated in the following table, diluteto the mark with a5% (V/V) solution of methanol-free ethanol in water, and mix. 5.3.2 Preparation of standard colorimetric so
26、lutions, for photometric measurements carried out in cells of optical path length1cm Into a series of six test tubes, place2,0ml of each of the dilute standard methanol solutions(5.3.1). 5.3.3 Colour development Add, to each tube,1,0ml of the potassium permanganate solution(3.1), and, after15min,0,6
27、ml of the disodium disulphite solution(3.2). To these solutions, which shall be colourless, add, while cooling with ice,10,0ml of the chromotropic acid solution(3.3), and heat on the water bath(4.1), controlled at70 2 C, for20min. Remove the tubes from the water bath and allow to cool. NOTE 1If the
28、colour of the compensation solution is more intense than that of the most dilute standard colorimetric solution, purify the chromotropic acid, or its disodium salt, as specified in3.3.2. NOTE 2Prepare a new calibration graph each time a new bottle of chromotropic acid is used. 5.3.4 Photometric meas
29、urements Carry out photometric measurements on each standard colorimetric solution(5.3.2) using either the spectrophotometer(4.2), set at a wavelength of about570nm, or the photoelectric absorptiometer(4.3) fitted with appropriate filters, after having adjusted the instrument to zero absorbance agai
30、nst a5% (V/V) solution of ethanol in water. 5.3.5 Plotting the graph Deduct the absorbance of the compensation solution from those of the standard colorimetric solutions(5.3.2). Plot a graph having, for example, the volumes, in millilitres, of methanol in the standard solutions(5.3.1) as abscissae a
31、nd the corresponding corrected values of absorbance as ordinates. 5.4 Determination 5.4.1 Colour development Take2,0ml of the test solution(5.1), place it in a test tube and proceed as specified in5.3.3. 5.4.2 Photometric measurements Carry out photometric measurements on the test solution and on th
32、e blank test solution, proceeding as specified in5.3.4, after having adjusted the instrument to zero absorbance against a5% (V/V) solution of ethanol in water. 6 Expression of results By means of the calibration graph(5.3.5), determine the volumes of methanol corresponding to the values of the photo
33、metric measurements. The methanol content, expressed as methanol as a percentage by volume, is given by the formula where Standard methanol solution(3.4) Corresponding volume of methanol ml ml 0 a 1,00 2,50 5,00 10,00 20,00 0 0,0005 0,00125 0,0025 0,005 0,010 a Compensation solution. V 0 is the volu
34、me, in millilitres, of methanol found in the blank test solution; V 1 is the volume, in millilitres, of methanol found in the test solution; V 2 is the volume, in millilitres, of the test portion. V 1 V 0 ()100 V 2 -BS6392-6:1983 BSI 12-1999 Publications referred to BS 1752, Laboratory sintered or f
35、ritted filters. ISO 4793, Laboratory sintered (fritted) filters Porosity grading, classification and designation 1) . 1) Referred to in the foreword only.BS 6392-6: 1983 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for prepa
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