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1、BRITISH STANDARD CONFIRMED APRIL 1993 BS 684-2.16: 1976 Methods of analysis of Fats and fatty oils Part 2: Other methods Section 2.16: Determination of copper colorimetric method IMPORTANT NOTE. It is essential that this Section be read in conjunction with the information in the “General introductio
2、n” to BS 684, which is published separately. UDC 665.1.014:543:543.432:546.56 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:34 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.16:1976 The British Standard, having been prepared under the direction of the Oils and Fats Standards Comm
3、ittee, 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 09405 7 A British Standard does not purport to include all the necessar
4、y 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 a
5、nd 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,
6、Wed Dec 06 13:16:34 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.16:1976 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 sheffieldu
7、n, na, Wed Dec 06 13:16:34 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:34 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.16:1976 BSI 12-19991 1 Scope This Section describes a method for the colorimetric determination of copper
8、 and 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 publications are referred to in this Section: BS 2021, S
9、eparating and dropping funnels. BS 2734, Boiling flasks (narrow-necked), conical, flat bottom and round bottom. 3 Principle The fat is digested with nitric acid, extracted with light petroleum and the aqueous layer is diluted. A solution of zinc dibenzyldithiocarbamate is added to the diluted aqueou
10、s layer and the mixture is filtered. The optical density of the filtrate is then determined. A reference curve is prepared using a standard copper solution. 4 Reagents The following reagents are required (see also BS 684: General introduction). 4.1 Light petroleum, boiling range between 40 C and 60
11、C. 4.2 Carbon tetrachloride 4.3 Hydrogen peroxide, solution, 300 g/l (100 vols). 4.4 Nitric acid, concentrated, 70 % (m/m) (16N). 4.5 Sulphuric acid, concentrated, 98 % (m/m) (36N). 4.6 Sulphuric acid, solution, 5 % (v/v). 4.7 Zinc dibenzyldithiocarbamate, solution, 5 g/l in carbon tetrachloride. 4.
12、8 Copper, standard solution, prepared by dissolving 0.157 g of copper sulphate pentahydrate (CuSO4.5H2O) in water containing 5 ml of sulphuric acid (4.6) and diluting to 200 ml (1 ml of the resulting solution N 200 4g of Cu). 5 Apparatus The following items of apparatus are required (see also BS 684
13、: General introduction). 5.1 Flasks, 250 ml capacity, round bottom, narrow-necked, complying with the requirements of BS 2734. 5.2 Separating funnels, 100 ml, complying with the requirements of BS 2021. 5.3 Spectrophotometer, capable of being operated in the region of 435 nm. Wash all glass apparatu
14、s with warm nitric acid solution, 5 % (v/v), and rinse several times with water before use. 6 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 t
15、est portion in the flask, 1 ml of water and 4 ml of nitric acid (4.4). Place the flask in a boiling 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
16、 by suction or siphon. Carefully warm the flask to expel the light petroleum from the aqueous layer, and heat the aqueous layer until the volume is reduced to about 0.5 ml. Add 0.5 ml of sulphuric acid (4.5) and a few drops of nitric acid (4.4). Heat until the mixture is nearly colourless. Complete
17、the digestion and destroy any nitrosyl sulphuric acid by adding two successive amounts of 0.3 ml of hydrogen peroxide (4.3), heating until white fumes are evolved after each addition. 7.3 Determination. Transfer the acid digest1) to a separating funnel (5.2) with 10 ml of water and make up to about
18、50 ml with sulphuric acid solution (4.6). Add 10 ml of the zinc dibenzyldithiocarbamate solution (4.7). Stopper the funnel and shake. Filter the lower layer through a plug of cotton wool introduced into the stem of the separating funnel. Measure the optical density of the extract with the spectropho
19、tometer (5.3) at a wavelength of 435 nm. Carry out a blank determination as described in 7.2 and 7.3, omitting the test portion. 1) The copper content of the acid digest should be within the range 5 4g to 15 4g. If it is greater than this, dilute the acid digest to a measured volume with water and t
20、ake an aliquot containing up to 15 4g of copper. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:34 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.16:1976 2 BSI 12-1999 7.4 Preparation of reference curve. Take exactly 2 ml of the standard copper solution (4.8) and make up to 200 ml
21、 with sulphuric acid solution (4.6) (1 ml of the resulting solution N 2 4g of Cu). Transfer suitable portions of this solution respectively to the appropriate number of separating funnels (5.2) to give a range of 0 4g to 20 4g of copper. Treat each portion of the standard solution as follows. Make u
22、p the volume to 50 ml with the sulphuric acid solution (4.6). Add 10 ml of zinc dibenzyldithiocarbamate solution (4.7). Stopper the funnel and shake. Filter the lower layer through a plug of cotton wool introduced into the stem of the separating funnel. Measure the optical density of the filtrate wi
23、th the spectrophotometer (5.3) at a wavelength of 435 nm. Prepare a reference curve by plotting the optical density as ordinate and copper content as abscissa. 8 Expression of results 8.1 Method of calculation. Express the copper content of the fat, read from the reference curve and taking into acco
24、unt 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. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:16:34 GMT+00:00 2006, Uncontrolled Copy, (c) BSI blank License
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