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1、BRITISH STANDARD CONFIRMED APRIL 1993 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 BS 684, which is published separately. UDC 665.1.014:543:543.432:546.72 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.17:1976 This British Standard, having been prepared under the direction of the Oils and Fats Standards Commi
3、ttee, was published under the authority of the Executive Board on 29 October 1976 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference OFC/24 Draft for comment 74/54405 DC ISBN 0 580 09445 6 A British Standard does not purport to include all the necessary
4、 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 from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 an
5、d 2 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. Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, W
6、ed Dec 06 13:16:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.17:1976 BSI 12-1999i Contents Page 1Scope1 2References1 3Principle1 4Reagents1 5Apparatus1 6Sampling and preparation of sample for analysis1 7Procedure1 8Expression of results2 9Test report2 Licensed Copy: sheffieldun sheffieldun
7、, na, Wed Dec 06 13:16:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.17:1976 BSI 12-19991 1 Scope This Section describes a method for the colorimetric determination of iron an
8、d is applicable to animal and vegetable fats. Methods for the determination of trace metals in fats using the atomic absorption spectrophotometric procedure are described in BS 684-2.18 (in course of preparation). 2 References The following standards publications are referred to in this Section: BS
9、1792, One-mark volumetric flasks. BS 2734, Boiling flasks (narrow-necked), conical, flat bottom and round bottom. 3 Principle The 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 titr
10、ated with congo red paper as indicator until the colour changes from blue to pink. 1-10 phenanthroline solution is then added and the optical density of the solution is determined. A reference curve is prepared using a standard iron solution. 4 Reagents The following reagents are required (see also
11、BS 684: General introduction). 4.1 Light petroleum, boiling range between 40 C and 60 C. 4.2 Hydrogen peroxide, solution, 300 g/l (100 vols). 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 acet
12、ate buffer solution, 340 g of sodium acetate trihydrate, 160 g of sodium hydroxide in 1 litre of water. 4.7 1-10 Phenanthroline solution. Dissolve 0.25 g of 1-10 phenanthroline hydrate in 20 ml of hot water containing two to three drops of sulphuric acid (4.4) and make up to 100 ml with water. Use a
13、 freshly prepared solution. 4.8 Iron, standard solution. Dissolve 8.635 g of ammonium ferric sulphate (NH4Fe(SO4)2.12H2O) in water containing 5 ml of sulphuric acid solution (1 vol of sulphuric acid (4.4) and 3 vol of water) and dilute to 1 litre. Before use, dilute this stock solution 100 times by
14、successive dilutions. (1 ml of the resulting solution N 10 4g of Fe.) 4.9 Congo red paper 5 Apparatus The following items of apparatus are required (see also BS 684: General introduction). 5.1 Flasks, 250 ml, round bottom, narrow-necked, complying with the requirements of BS 2734. 5.2 Volumetric fla
15、sks, 25 ml, complying with the requirements of BS 1792. 5.3 Spectrophotometer, or other suitable instrument with a filter giving a maximum transmission over the range 490 nm to 520 nm. Wash all glass apparatus with warm nitric acid solution 5 % (v/v) and rinse several times with water before use. 6
16、Sampling and preparation of sample for analysis See BS 684: General introduction. 7 Procedure 7.1 Test portion. Weigh, to the nearest 10 mg, 25 g of the fat into the flask (5.1). 7.2 Digestion. Add to the test portion in the flask 1 ml of water and 4 ml of nitric acid (4.3). Place the flask in a boi
17、ling water bath for 15 min to 20 min, swirling frequently. Cool the flask to a temperature of about 40 C and extract with three successive portions of light petroleum (4.1) drawing off the petroleum layer by suction or siphon. Warm cautiously to expel the light petroleum from the aqueous layer and h
18、eat the aqueous layer until the volume is reduced to about 0.5 ml. Add 0.5 ml of sulphuric acid (4.4) and a few drops of nitric acid (4.3) and heat until the mixture is almost colourless. Complete the digestion and destroy any nitrosyl sulphuric acid by adding two successive amounts of 0.3 ml of hyd
19、rogen peroxide (4.2), heating until white fumes appear after each addition. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.17:1976 2 BSI 12-1999 7.3 Determination. Transfer the acid digest1) to a 25 ml volumetric flask (5.2), dilut
20、e to 10 ml to 15 ml with water, add 1 ml to 2 ml 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. Add 2 ml of 1-10 phenanthroline solution
21、 (4.7), make up to volume, mix, and stand in the dark for 1 h. Measure the optical density of the solution with the spectrophotometer (5.3) at a wavelength of 510 nm. Carry out a blank determination as described in 7.2 and 7.3, omitting the test portion. 7.4 Preparation of reference curve. Dilute th
22、e standard solution of iron (4.8) to a concentration of 5 4g of iron per millilitre. Transfer suitable portions of this solution respectively to the appropriate number of volumetric flasks (5.2) to give a range of 0 4g to 50 4g of iron. Treat each portion of the standard solution as follows. Add 1 m
23、l to 2 ml 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. Add 2 ml of 1-10 phenanthroline solution (4.7). Make up to volume, mix, and s
24、tand in the dark for 1 h. Measure the optical densities of the solutions. 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
25、into account the result of the blank determination, in milligrams per kilogram of fat. 9 Test report See the general instructions and recommendations given in BS 684: General introduction. 1) The iron content of the acid digest should be within the range 5 4g to 40 4g. If the iron content is greater
26、 than 40 4g, dilute the acid digest a measured volume with water and take an aliquot containing up to 40 4g of iron. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:36 GMT+00
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