1、BRITISH STANDARD CONFIRMED APRIL1993 BS684-2.16: 1976 Methods of analysis of Fats and fatty oils Part2: Other methods Section2.16: Determination of coppercolorimetric method IMPORTANT NOTE. It is essential that this Section be read in conjunction with the information inthe “General introduction” to
2、BS684, which is published separately. UDC 665.1.014:543:543.432:546.56BS684-2.16:1976 The BritishStandard, having beenprepared under the directionof the Oils and Fats Standards Committee, was published under the authority ofthe Executive Board on 29October1976 BSI12-1999 The following BSI references
3、 relate to the work on this standard: Committee reference OFC/24 Draft for comment74/54405 DC ISBN 0 580 09405 7 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 Brit
4、ish 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 b
5、e indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date of issue CommentsBS684-2.16:1976 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 Procedu
6、re 1 8 Expression of results 2 9 Test report 2ii blankBS684-2.16:1976 BSI 12-1999 1 1 Scope This Section describes a method for the colorimetric determination of copper 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 publications are referred to in this Section: BS2021, Separating and dropping funnels. BS2734, Boiling flasks (narrow-necked), conical, flat bottom and round bottom. 3 Principle The fat is
8、digested with nitric acid, extracted with light petroleum and the aqueous layer is diluted. A solution of zinc dibenzyldithiocarbamate is added to the diluted aqueous layer and the mixture is filtered. The optical density of the filtrate is then determined. A reference curve is prepared using a stan
9、dard copper solution. 4 Reagents The following reagents are required (seealsoBS684: General introduction). 4.1 Light petroleum, boiling range between40 C and60 C. 4.2 Carbon tetrachloride 4.3 Hydrogen peroxide, solution,300g/l(100vols). 4.4 Nitric acid, concentrated,70%(m/m)(16N). 4.5 Sulphuric acid
10、, concentrated,98%(m/m)(36N). 4.6 Sulphuric acid, solution,5%(v/v). 4.7 Zinc dibenzyldithiocarbamate, solution,5g/l in carbon tetrachloride. 4.8 Copper, standard solution, prepared by dissolving0.157g of copper sulphate pentahydrate (CuSO 4 .5H 2 O) in water containing5ml of sulphuric acid(4.6) and
11、diluting to200ml(1ml of the resulting solutionN 2004g of Cu). 5 Apparatus The following items of apparatus are required (seealso BS684: General introduction). 5.1 Flasks,250ml capacity, round bottom, narrow-necked, complying with the requirements of BS2734. 5.2 Separating funnels,100ml, complying wi
12、th the requirements of BS2021. 5.3 Spectrophotometer, capable of being operated in the region of435nm. Wash all glass apparatus 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 BS684: General introduction. 7
13、Procedure 7.1 Test portion. Weigh, to the nearest10mg,25g of the fat into the flask(5.1). 7.2 Digestion. Add to the test portion in the flask,1ml of water and4ml of nitric acid(4.4). Place the flask in a boiling water bath for15min to20min, swirling frequently. Cool the flask to a temperature of abo
14、ut40 C and extract with three successive portions of light petroleum(4.1), drawing off the petroleum layer 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 about0.5ml. Add0.5ml of sulphuric a
15、cid(4.5) and a few drops of nitric acid(4.4). Heat until the mixture is nearly colourless. Complete the digestion and destroy any nitrosyl sulphuric acid by adding two successive amounts of0.3ml of hydrogen peroxide(4.3), heating until white fumes are evolved after each addition. 7.3 Determination.
16、Transfer the acid digest 1)to a separating funnel(5.2) with10ml of water and make up to about50ml with sulphuric acid solution(4.6). Add10ml 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
17、of the separating funnel. Measure the optical density of the extract with the spectrophotometer(5.3) at a wavelength of435nm. Carry out a blank determination as described in7.2 and7.3, omitting the test portion. 1) The copper content of the acid digest should be within the range54g to154g. If it is
18、greater than this, dilute the acid digest to a measured volume with water and take an aliquot containing up to154g of copper.BS684-2.16:1976 2 BSI 12-1999 7.4 Preparation of reference curve. Take exactly2ml of the standard copper solution(4.8) and make up to200ml with sulphuric acid solution(4.6)(1m
19、l of the resulting solutionN 24g of Cu). Transfer suitable portions of this solution respectively to the appropriate number of separating funnels(5.2) to give a range of04g to204g of copper. Treat each portion of the standard solution as follows. Make up the volume to50ml with the sulphuric acid sol
20、ution(4.6). Add10ml 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 with the spectrophotometer(5.3) at a wavelength of435nm
21、. 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 account the result of the blank determination, in milligrams
22、 per kilogram of fat. 9 Test report See the general instructions and recommendations given in BS684: General introduction.blankBS684-2.16: 1976 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It
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