BS 684-1 6-1988 Methods of analysis of fats and fatty oils - Physical methods - Determination of titre《脂肪和油脂的分析方法 物理法 滴定度的测定》.pdf

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1、BRITISH STANDARD CONFIRMED APRIL1993 BS684-1.6: 1988 ISO935:1988 Methods of analysis of Fats and fatty oils Part1: Physical methods Section 1.6 Determination of titre ISO title: Animal and vegetable fats and oils Determination of titre IMPORTANT NOTE. It is essential that BS684-0, which is published

2、 separately, be read inconjunction with this Section. UDC665.1.014:665.2/.3:665.7:620.171.32:620.1:(083.71)BS684-1.6:1988 This British Standard, having been prepared under the directionof the Food and Agriculture Standards Committee,was published underthe authority of the BoardofBSI and comes into e

3、ffect on 30 November1988 BSI10-1999 First published October1976 First revision November 1988 The following BSI references relate to the work on this standard: Committee reference FAC/18 Draft for comment86/53151DC ISBN 0 580 16972 3 National foreword This Section of BS684 has been prepared under the

4、 direction of the Food and Agriculture Standards Committee and supersedes BS684-1.6:1976 which is withdrawn. It is identical with ISO935:1988 “Animal and vegetable fats and oils Determination of titre” published by the International Organization for Standardization (ISO) and in the preparation of wh

5、ich the UnitedKingdom played a full part. The principal differences from the1976 edition are that saponification is carried out in glycerol and not ethanol solution and stirring is continuous during the determination of titre. Terminology and conventions. The text of the International Standard has b

6、een approved as suitable 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 c

7、urrent practice to use a full point on the baseline as the decimal marker. The symbol “l” has been used to denote litre (and in its submultiples). InBritish Standards it is current practice to use the symbol “L”. In BritishStandards it is current practice to use the spelling “sulphur”, etc., instead

8、 of “sulfur”, etc. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Section of BS684”. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct applic

9、ation. 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, an inside back cover and a back cover. This standard has been updated (see copyright date) and

10、 may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Cross-references International Standard Corresponding British Standard ISO661:1980 BS684 Methods of analysis of fats and fatty oils Part0:1982 General introduction Appendix B (Identical) I

11、SO5555:1983 BS627:1982 Methods for sampling animal and vegetable fats and oils (Technically equivalent) Amendments issued since publication Amd. No. Date of issue CommentsBS684-1.6:1988 BSI 10-1999 i Contents Page National foreword Inside front cover 1 Scope and field of application 1 2 References 1

12、 3 Definition 1 4 Principle 1 5 Reagents 1 6 Apparatus 1 7 Sampling 1 8 Preparation of test sample 1 9 Procedure 1 10 Expression of results 2 11 Test report 2 Figure Cooling apparatus 3 Publications referred to Inside back coverii blankBS684-1.6:1988 BSI 10-1999 1 1 Scope and field of application Th

13、is International Standard specifies a method for the preparation of the water-insoluble fatty acids of animal and vegetable fats and oils and the determination of their solidification temperature, called conventionally the titre of the fat or oil. The method is not applicable to fats and oils the ti

14、tre of which is below30 C. 2 References ISO661, Animal and vegetable fats and oils Preparation of test sample. ISO5555, Animal and vegetable fats and oils Sampling. 3 Definition For the purposes of this International Standard, the following definition applies. titre constant temperature observed whe

15、n there is a temporary halt in the fall in temperature or, if there is an increase in temperature, the maximum temperature reached during the cooling, with continuous stirring, of liquid fatty acids 4 Principle Saponification of a test portion with potassium hydroxide solution in glycerol, dissoluti

16、on of the soap in water and neutralization. Washing of the separated insoluble fatty acids with hot sodium chloride solution, drying and filtering. Melting of the prepared fatty acids, cooling them, with continuous stirring, and observation of the solidification temperature as shown by a halt in the

17、 fall of temperature, possibly accompanied by a temporary rise in temperature. 5 Reagents All reagents shall be of recognized analytical quality and the water used shall be distilled water or water of at least equivalent purity. 5.1 Potassium hydroxide, solution in glycerol, prepared by dissolving10

18、0g of potassium hydroxide in500g of glycerol by heating to not more than130 C. Foaming may occur at higher temperatures. 5.2 Sulfuric acid, solution prepared by carefully adding1 volume of concentrated sulfuric acid ( =1,84g/ml) to4 volumes of water, while stirring. 5.3 Sodium chloride,100g/l soluti

19、on. 5.4 Sodium sulfate, anhydrous. 5.5 Methyl orange,5g/l indicator solution. 6 Apparatus Usual laboratory apparatus and in particular 6.1 Flat-bottomed flask or beaker, of1 litre capacity, made of borosilicate glass. 6.2 Electric hotplate, capable of being controlled at approximately130 and at140 1

20、0 C, preferably having a magnetic stirrer. 6.3 Separating funnel, of500ml capacity. 6.4 Cooling apparatus, fitted with an apparatus suitable for continuous stirring(seetheFigure). 6.4.1 Wide-necked jar, of height130mm and external diameter100mm. 6.4.2 Test tube,100mm 25mm, fitted with a stirrer that

21、 can be operated continuously and move through a vertical distance of about40mm. The test tube may be marked at a height of55mm. The stirrer shall be made of glass or inert metal2 to3mm in diameter, with the bottom end bent to form a complete circle19mm in diameter in the horizontal plane. 6.4.3 Fla

22、t cork, to fit the jar(6.4.1) and with a central hole to support the test tube(6.4.2). 6.4.4 Thermometer, graduated in0,1 C divisions, calibrated for the temperature range within which the titre falls and suitable to be suspended so that the bulb is about10mm from the bottom of the test tube(6.4.2).

23、 6.5 Water (or other liquid) bath, capable of being maintained at a temperature20 to25 C below the expected titre. 7 Sampling See ISO5555. 8 Preparation of test sample Prepare the test sample in accordance with ISO661. 9 Procedure 9.1 Preparation of fatty acids insoluble in water Weigh about110g of

24、the potassium hydroxide solution(5.1) into the1 litre flask or beaker(6.1). Stir and heat on the hot plate(6.2) to about130 C. Add about45g of the test sample (clause8) heated to about60 C. Stir the mixture on the hotplate, controlled at140 10 C, until the saponification is complete, as indicated by

25、 the mixture becoming transparent and homogeneous with the formation of a foam persisting for a few minutes when stirring and heating are stopped.BS684-1.6:1988 2 BSI 10-1999 Allow the temperature to drop to about105 C. Add300ml of hot water, with stirring. Stir and heat (to boiling if necessary) un

26、til the soap is completely dissolved. Add the sulfuric acid solution(5.2), usually about50ml, with stirring, until the mixture is neutral to methyl orange(5.5). Continue heating and stirring until the fatty acids form a clear liquid surface layer. NOTEIf short-chain fatty acids are present, heat the

27、 acidified mixture under reflux. Transfer the hot mixture to the separating funnel(6.3). Draw off and reject the aqueous layer. Wash the fatty acids with three150ml portions of the sodium chloride solution(5.3) which is hot enough to maintain the fatty acids in a liquid state. After each washing, dr

28、aw off the aqueous layer as completely as possible and reject it. Transfer the fatty acids to a100ml beaker, add approximately5g of the anhydrous sodium sulfate(5.4) and stir. Filter through a dry filter paper, ensuring that the fatty acids remain liquid. 9.2 Determination of titre Heat the fatty ac

29、ids(9.1) to about10 C above the expected titre. Pour into the test tube(6.4.2) to a height of55mm, assemble the cooling apparatus(6.4) and place it in the bath(6.5). Immediately operate the stirrer at a rate of80 to100 complete up-and-down motions per minute. Observe the temperature which, after a r

30、apid initial decrease, falls slowly as crystallization starts and then becomes constant or rises within30s. Stop the stirring. Record to the nearest0,1 C either the constant temperature or the maximum temperature reached in any rise as the titre. 9.3 Number of determinations Carry out a two determin

31、ations(9.2) on the same prepared fatty acids(9.1). 10 Expression of results 10.1 Method of calculation Take as the result the arithmetic mean of the two determinations(9.3), provided that the requirements for repeatability(10.2) are met. Otherwise carry out two more determinations on the same prepar

32、ed fatty acids(9.1). Express the result to the nearest0,1 C. 10.2 Repeatability The difference between the values of two determinations carried out in rapid succession by the same analyst on the same prepared fatty acids shall not exceed0,2 C. NOTEThe figure of0,2 C has been accepted historically in

33、 several countries. Recent tests have not shown any reason to disagree with this Figure. 11 Test report The test report shall show the method used and the result obtained. It shall also mention any operating conditions not specified in this International Standard or regarded as optional, as well as

34、any circumstances that may have influenced the result. The test report shall include all details required for the complete identification of the sample. BS684-1.6:1988 BSI 10-1999 3 Figure Cooling apparatus4 blankBS684-1.6:1988 BSI 10-1999 Publications referred to See national foreword.BS684-1.6: 19

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