1、BRITISH STANDARD BS6392-4: 1983 Incorporating Amendment No.1 Testing of ethanol for industrial use Part4: Method for determination of aldehydes content NOTEIt is recommended that this Part be read in conjunction with the information given in the“General introduction” published separately as BS6392-0
2、. UDC661.722:543.432.062:547.281BS6392-4:1983 This British Standard, having been prepared under the directionof the Chemicals Standards Committee, was published under the authority ofthe Board of BSI and comes intoeffect on 31August1983 The Committees responsible forthis British Standard are shown i
3、n part 0 BSI10-1999 The following BSI references relate to the work on this standard: Committee reference CIC/4 Draft for comment80/51209 DC ISBN0 580 13370 2 Foreword This Part of BS6392 is technically equivalent to ISO1388“Ethanol for industrial useMethods of test” Part5 “Determination of aldehyde
4、s content Visual colorimetric method”, published in1981 by the International Organization for Standardization (ISO). For ease of production, the text of ISO1388-5:1981, with the omission of the Annex, has been used for this British Standard. Some terminology and certain conventions are not identical
5、 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 on the baseline as the decimal marker. This standard describes a method only and should not be used as a
6、 specification defining limits of purity. Reference to the standard should indicate that the method of test used is in accordance with BS6392-4. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct app
7、lication. 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 and ii, pages1 and2, an inside back cover and a back cover. This standard has been updated (see copyright date
8、) 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 4940 March1986 Indicated by a sideline in the marginBS6392-4:1983 BSI 10-1999 i Contents Page Foreword Inside front
9、 cover 1 Scope and field of application 1 2 Principle 1 3 Reagents 1 4 Apparatus 2 5 Procedure 2 6 Expression of results 2 Publication referred to Inside back coverii blankBS6392-4:1983 BSI 10-1999 1 1 Scope and field of application This Part of BS6392 describes a visual colorimetric method for the
10、determination of the aldehydes content of ethanol for industrial use. The method is applicable to products having aldehyde contents, expressed as acetaldehyde, in the range0,00025 to0,00125%(m/m). NOTEThe title of the publication referred to in this standard is given on inside back cover. 2 Principl
11、e Reaction of the aldehydes present in a test portion with Schiff reagent. Visual comparison of the colour obtained with the colours of standard colorimetric solutions containing known quantities of acetaldehyde. 3 Reagents During the analysis, use only reagents of recognized analytical grade, and d
12、istilled water or water of equivalent purity. 3.1 Ethanol, 95%(V/V), aldehydes-free, purified as follows. Boil1500ml of absolute ethanol, under reflux, for2h, with15g of m-phenylenediamine. Distil the mixture, rejecting the first and last50ml fractions of the distillate. Adjust the concentration to9
13、5%(V/V) by adding an appropriate volume of water and mix. Use the procedure specified in clause5 to verify that the purified ethanol is free from aldehydes. NOTEIndustrial methylated spirits95%(V/V) is not suitable for use in place of the absolute ethanol used in the preparation of this reagent. WAR
14、NINGm-Phenylenediamine is toxic by inhalation, in contact with the skin and if swallowed. Avoid contact with skin and eyes, and inhalation of the dust. 3.2 Schiff reagent WARNINGBasic fuchsin is carcinogenic. Avoid skin contact with basic fuchsin and its solutions and inhalation of its dust. 3.2.1 P
15、reparation Place1500ml of water in a3000ml conical flask, add4,500 0,005g of p-rosaniline hydrochloride (basic fuchsin), and swirl to dissolve. Add9,60 0,05g of disodium disulphite sodium metabisulphite (Na 2 S 2 O 5 ), mix and allow to stand for5 to10min. Add40ml of approximately295g/l sulphuric ac
16、id solution, mix thoroughly, stopper the flask and allow to stand for about12h. Decolorize the solution if necessary, by treatment with activated carbon. 3.2.2 Determination and adjustment of free sulphur dioxide content Transfer10ml of the colourless reagent(3.2.1) to a250ml conical flask. Add20ml
17、of water and5ml of freshly prepared starch solution, and titrate the solution with standard volumetric iodine solution, c(1/2l 2 )=0,1mol/l, until the characteristic dark blue colour is just obtained. NOTE1ml of iodine solution, c(1/2l 2 )=0,1mol/l, corresponds to0,0032g ofSO 2 . If the free sulphur
18、 dioxide content does not fall within the optimum range (0,18 to0,31g per100ml of reagent), adjust it as appropriate, increasing the level by adding a calculated quantity of disodium disulphite or decreasing it by bubbling air through the reagent solution. 3.3 Acetaldehyde, standard solution corresp
19、onding to1g of acetaldehyde per litre. Weigh, to the nearest0,0001g,0,6930g of acetaldehyde ammonia CH 3 CH(NH 2 )OH and dissolve it in the ethanol(3.1). Transfer the solution quantitatively to a500ml one-mark volumetric flask, dilute to the mark with ethanol of the same quality and mix. 1ml of this
20、 standard solution contains0,001g of acetaldehyde. NOTE 1If acetaldehyde ammonia of analytical grade is not available, purify the commercial product as follows. Dissolve about5g of acetaldehyde ammonia in a small quantity of absolute ethanol and precipitate it by adding twice the volume of dry dieth
21、yl ether (C 2 H 5 OC 2 H 5 ). Using a Buchner funnel, filter the precipitate and, after washing it with more of the diethyl ether, transfer it immediately to a vacuum desiccator containing sulphuric acid,A approximately1,84g/ml,98%(m/m) solution, as desiccant, and allow to dry for3 to4h. Repeat the
22、purification if necessary, until the product is colourless. NOTE 2Industrial methylated spirits95%(V/V) is not suitable for use in place of the absolute ethanol used in purifying the acetaldehyde ammonia. WARNINGDiethyl ether is highly flammable and its vapour is harmful. Avoid breathing vapour. 3.4
23、 Acetaldehyde, standard solution corresponding to0,1g of acetaldehyde per litre. Transfer25,0ml of the standard acetaldehyde solution(3.3) to a250ml one-mark volumetric flask, dilute to the mark with the ethanol(3.1) and mix. 1ml of this standard solution contains0,0001g of acetaldehyde.BS6392-4:198
24、3 2 BSI 10-1999 4 Apparatus Ordinary laboratory apparatus, and 4.1 Colorimetric tubes, fitted with ground glass stoppers, of capacity about20ml, and graduated at10 and14ml. 4.2 Graduated pipettes, of capacity5ml, graduated in0,02ml divisions. 5 Procedure 5.1 Test portion Using one of the graduated p
25、ipettes(4.2), measure3,0ml of the laboratory sample into one of the colorimetric tubes(4.1). 5.2 Preparation of the test solution and standard colorimetric solutions Into a series of six100ml one-mark volumetric flasks, place the volumes of the standard acetaldehyde solution(3.4) indicated in the fo
26、llowing table, dilute to the mark with the ethanol(3.1) and mix. Using the graduated pipettes(4.2), measure, into a series of six of the colorimetric tubes(4.1),3,0ml of each of these diluted standard acetaldehyde solutions. Treat the contents of each tube, including those of the tube containing the
27、 test portion(5.1), as follows. Dilute to10ml with water and add sufficient of the Schiff reagent(3.2) to bring the volume to14ml. Stopper the tubes, mix the solutions (preferably simultaneously) and allow to stand in a rack for25min. 5.3 Determination Compare the colour of the test solution with th
28、e colours of the standard colorimetric solutions, in dispersed daylight. NOTEIf the colour of the test solution is deeper than that of the most concentrated standard colorimetric solution, repeat the test using more of the laboratory sample suitably diluted with the ethanol(3.1), and take this into
29、account in the calculation of results. 6 Expression of results The aldehydes content, expressed as acetaldehyde (CH 3 CHO) as a percentage by mass, is given by the formula where m is the mass, in grams (seethe table), of acetaldehyde used to prepare the diluted standard solution giving a colour matc
30、hing most closely that developed in the test solution. is the density, in grams per millilitre, of the sample at20 C (seeBS4522); Standard acetaldehyde solution(3.4) Corresponding mass of acetaldehyde ml g 2,0 3,0 5,0 7,0 9,0 10,0 0,0002 0,0003 0,0005 0,0007 0,0009 0,0010m -BS6392-4:1983 BSI 10-1999
31、 Publication referred to BS4522, Method for the determination of density of liquids at20 C. BS6392-4: 1983 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in
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