BS 684-2 17-1976 Methods of analysis of fats and fatty oils - Other methods - Determination of iron - Colorimetric method《脂肪和油脂的分析方法 其他方法 铁的测定 比色法》.pdf

1、BRITISH STANDARD CONFIRMED APRIL1993 BS 684-2.17: 1976 Methods of analysis of Fats and fatty oils Part 2: Other methods Section 2.17: Determination of iron colorimetric method IMPORTANT NOTE. It is essential that this Section be read in conjunction with the information in the “General introduction”

2、to BS684, which is published separately. UDC 665.1.014:543:543.432:546.72BS684-2.17:1976 This British Standard, having been prepared under the directionof the Oils and FatsStandards Committee, waspublished under the authorityofthe Executive Boardon 29October1976 BSI 12-1999 The following BSI referen

3、ces relate to the work on this standard: Committee reference OFC/24 Draft for comment74/54405DC ISBN 0 580 09445 6 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 Br

4、itish 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 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will

5、 be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date of issue CommentsBS684-2.17:1976 BSI 12-1999 i Contents Page 1 Scope 1 2 References 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Sampling and preparation of sample for analysis 1 7 Proce

6、dure 1 8 Expression of results 2 9 Test report 2ii blankBS684-2.17:1976 BSI 12-1999 1 1 Scope This Section describes a method for the colorimetric determination of iron and is applicable to animal and vegetable fats. Methods for the determination of trace metals in fats using the atomic absorption s

7、pectrophotometric procedure are described in BS684-2.18 (in course of preparation). 2 References The following standards publications are referred to in this Section: BS 1792, One-mark volumetric flasks. BS 2734, Boiling flasks (narrow-necked), conical, flat bottom and round bottom. 3 Principle The

8、fat is digested with nitric acid and extracted with light petroleum. The aqueous layer is diluted, sulphur dioxide solution is added and the diluted aqueous layer is titrated with congo red paper as indicator until the colour changes from blue to pink.1-10 phenanthroline solution is then added and t

9、he optical density of the solution is determined. A reference curve is prepared using a standard iron solution. 4 Reagents The following reagents are required (seealsoBS684: General introduction). 4.1 Light petroleum, boiling range between40 C and60 C. 4.2 Hydrogen peroxide, solution,300g/l(100 vols

10、). 4.3 Nitric acid, concentrated,70%(m/m)(16N). 4.4 Sulphuric acid, concentrated, 98%(m/m)(36N). 4.5 Sulphur dioxide, solution,2%(m/m). 4.6 Sodium acetate buffer solution, 340g of sodium acetate trihydrate,160g of sodium hydroxide in1litre of water. 4.7 1-10 Phenanthroline solution. Dissolve0.25g of

11、1-10 phenanthroline hydrate in20ml of hot water containing two to three drops of sulphuric acid(4.4) and make up to100ml with water. Use a freshly prepared solution. 4.8 Iron, standard solution. Dissolve8.635g of ammonium ferric sulphate (NH 4 Fe(SO 4 ) 2 .12H 2 O) in water containing5ml of sulphuri

12、c acid solution(1vol of sulphuric acid(4.4) and3 vol of water) and dilute to1litre. Before use, dilute this stock solution100 times by successive dilutions.(1ml of the resulting solutionN 104g ofFe.) 4.9 Congo red paper 5 Apparatus The following items of apparatus are required (seealso BS684: Genera

13、l introduction). 5.1 Flasks, 250ml, round bottom, narrow-necked, complying with the requirements of BS2734. 5.2 Volumetric flasks, 25ml, complying with the requirements of BS1792. 5.3 Spectrophotometer, or other suitable instrument with a filter giving a maximum transmission over the range490nm to52

14、0nm. Wash all glass apparatus with warm nitric acid solution5%(v/v) and rinse several times with water before use. 6 Sampling and preparation of sample for analysis See BS684: General introduction. 7 Procedure 7.1 Test portion. Weigh, to the nearest10mg,25g of the fat into the flask(5.1). 7.2 Digest

15、ion. Add to the test portion in the flask1ml of water and4ml of nitric acid(4.3). Place the flask in a boiling water bath for15min to20min, swirling frequently. Cool the flask to a temperature of about40 C and extract with three successive portions of light petroleum(4.1) drawing off the petroleum l

16、ayer by suction or siphon. Warm cautiously to expel the light petroleum from the aqueous layer and heat the aqueous layer until the volume is reduced to about0.5ml. Add0.5ml of sulphuric acid(4.4) and a few drops of nitric acid(4.3) and heat until the mixture is almost colourless. Complete the diges

17、tion and destroy any nitrosyl sulphuric acid by adding two successive amounts of0.3ml of hydrogen peroxide(4.2), heating until white fumes appear after each addition.BS684-2.17:1976 2 BSI 12-1999 7.3 Determination. Transfer the acid digest 1)to a25ml volumetric flask(5.2), dilute to10ml to15ml with

18、water, add1ml to2ml of sulphur dioxide solution(4.5) and a small square of congo red paper(4.9). Titrate the mixture dropwise with the sodium acetate buffer solution(4.6) until the colour of the paper changes from blue to pink. Add2ml of1-10 phenanthroline solution(4.7), make up to volume, mix, and

19、stand in the dark for1h. Measure the optical density of the solution with the spectrophotometer(5.3) at a wavelength of510nm. Carry out a blank determination as described in7.2 and7.3, omitting the test portion. 7.4 Preparation of reference curve. Dilute the standard solution of iron(4.8) to a conce

20、ntration of54g of iron per millilitre. Transfer suitable portions of this solution respectively to the appropriate number of volumetric flasks(5.2) to give a range of04g to504g of iron. Treat each portion of the standard solution as follows. Add1ml to2ml of sulphur dioxide solution(4.5) and a small

21、square of congo red paper(4.9). Titrate the mixture, dropwise, with the sodium acetate buffer solution(4.6) until the colour of the paper changes from blue to pink. Add2ml of1-10 phenanthroline solution(4.7). Make up to volume, mix, and stand in the dark for1h. Measure the optical densities of the s

22、olutions. Prepare a reference curve by plotting the optical density as ordinate and iron content as abscissa. 8 Expression of results 8.1 Method of calculation. Express the iron content of the fat, read from the reference curve, taking into account the result of the blank determination, in milligram

23、s per kilogram of fat. 9 Test report See the general instructions and recommendations given in BS684: General introduction. 1) The iron content of the acid digest should be within the range54g to404g. If the iron content is greater than404g, dilute the acid digest a measured volume with water and ta

24、ke an aliquot containing up to404g of iron.blankBS 684-2.17: 1976 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 Europe and at the international level. It

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