1、BRITISH STANDARD BS7319-7: 1990 Analysis of sodiumchloride forindustrial use Part7: Method for determination of copper contentBS7319-7:1990 This BritishStandard, having been prepared under the directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Board ofBSIand
2、comes into effect on 30September1990 BSI 11-1999 The following BSI references relate to the work on this standard: Committee references CIC/22, FAC/23 Draft for comment 88/55620 DC ISBN 0 580 18540 0 Committees responsible for this BritishStandard The preparation of this BritishStandard was entruste
3、d by the Chemicals Standards Policy Committee (CIC/-) to Technical Committee CIC/22, upon which the following bodies were represented: British Association for Chemical Specialities Chemical Industries Association Man-made Fibres Producers Committee Soap and Detergent Industry Association Textile Res
4、earch Council (FCRA) The following bodies were also represented in the drafting of the standard, through Technical Committee FAC/23: AFRC Institute of Food Research Creamery Proprietors Association Department of Trade and Industry (Laboratory of the Government Chemist) Food and Drink Federation Milk
5、 Marketing Board for Northern Ireland Royal Association of British Dairy Farmers Salt Manufacturers Association Amendments issued since publication Amd. No. Date CommentsBS7319-7:1990 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagents
6、 1 4 Apparatus 1 5 Procedure 1 6 Expression of results 2 7 Precision 3 Table 1 Mass of copper in standard solutions 1 Table 2 Statistical results of sodium chloride analysis 3 Publications referred to Inside back coverBS7319-7:1990 ii BSI 11-1999 Foreword BS7319 has been prepared, under the directio
7、n of the Chemicals Standards Policy Committee, at the request of Technical Committee FAC/23, Salt, primarily to provide appropriate methods for determination of vacuum salt for food use as specified in BS998:1990. The methods for determination were previously published as appendices to BS998:1969. A
8、 list of the Parts of BS7319 is given in Part1. This Part of BS7319 is based upon a method developed on behalf of the European Committee for the Study of Salt. It supersedes Appendix L of BS998:1969 which is withdrawn. A British Standard does not purport to include all the necessary provisions of a
9、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, pagesi andii, pages1 to4, an inside back co
10、ver 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.BS7319-7:1990 BSI 11-1999 1 1 Scope This Part of BS7319 describes a photometric method, using zinc dibenzyldithi
11、ocarbamate for the determination of copper in sodium chloride. The method is applicable to products having copper contents equal to or greater than0.01mg/kg. NOTEThe titles of the publications referred to in this Part of this BritishStandard are listed on the inside back cover. 2 Principle The princ
12、iple of this Part of BS7319 is the formation of a coloured complex by reaction of the copper with zinc dibenzyldithiocarbamate and photometric measurement at a wavelength of approximately435nm. NOTEBy carrying out the determination in acid medium, interferences, especially from iron, manganese, nick
13、el and cobalt, are suppressed or much reduced. 3 Reagents 3.1 General. Use only reagents of recognized analytical grade and only water complying with grade3 of BS3978. 3.2 Carbon tetrachloride, redistilled. 3.3 Hydrochloric acid, c(HCl)=2mol/L. Dilute160mL of hydrochloric acid, =1.19g/mL, to1000mL w
14、ith water. 3.4 Zinc dibenzyldithiocarbamate, 0.5g/L solution in carbon tetrachloride. Dissolve0.5g of zinc dibenzyldithiocarbamate in100mL of carbon tetrachloride(3.2). 3.5 Copper stock solution, 0.100g of Cu per litre. Weigh, to the nearest0.0001g,0.393g of copper(II) sulphate pentahydrate (CuSO 4
15、.5H 2 O) and transfer to a1000mL one-mark volumetric flask. Add approximately50mL of water and swirl until the salt has dissolved. Add50mL of the hydrochloric acid solution(3.3), dilute to the mark with water, and mix well. Make this solution freshly each week. 1mL of this solution contains100g of C
16、u. 3.6 Copper standard solution, 0.0010g of Cu per litre. Introduce10.0mL of the stock copper solution(3.5) into a1000mL one-mark volumetric flask, dilute to the mark with water and mix well. 1mL of this standard solution contains1g of Cu. Prepare this solution at the time of use. 4 Apparatus 4.1 Or
17、dinary laboratory apparatus 4.2 Spectrometer, or photometer, fitted with filters having a maximum transmission between430nm and440nm. 4.3 Burette, 25mL, graduated in0.02mL. 5 Procedure CAUTION. Ensure that no trace of copper is introduced during the analysis by the reagents, the water or the apparat
18、us, especially the apparatus used in the preparation of the initial sample. 5.1 General Wash all new glassware used in the determination as follows: a) with brush and soap if the sides are greasy; b) with concentrated nitric acid, followed by several rinses with water. Use the glassware a few times
19、before carrying out an actual determination. Then keep exclusively for the determination of copper. 5.2 Test portion Weigh, to the nearest0.1g, a test portion of approximately100g. 5.3 Blank test At the same time as the determination carry out a blank test following the same procedure and using the
20、same quantities of all the reagents used for the determination but omitting the test portion. 5.4 Preparation of the calibration curve 5.4.1 Preparation of the standard colorimetric solutions Introduce, from the burette(4.3), into a series of five500mL separating funnels, each containing25mL of the
21、hydrochloric acid(3.3), the volumes of the copper standard solution(3.6) shown in Table 1. Table 1 Mass of copper in standard solutions NOTEThe calibration can be extended, if necessary. The curve is linear up to50g of Cu. Standard copper solution(3.6) Corresponding mass of copper mL g 0 a 2.5 5.0 7
22、.5 10.0 0 2.5 5.0 7.5 10.0 a Zero standard.BS7319-7:1990 2 BSI 11-1999 5.4.2 Formation of the coloured complex Dilute the contents of each separating funnel to approximately250mL with water, and mix. Add25.0mL of the zinc dibenzyldithiocarbamate solution(3.4). Stopper, shake well for1min and allow t
23、he layers to separate. Run the lower layer through a hydrophobic filter paper into a cell of optical path length4cm. NOTECells of path length5cm may be used if4cm cells are not available. 5.4.3 Photometric measurements Adjust the apparatus to zero absorbance with respect to carbon tetrachloride(3.2)
24、 prior to each measurement. Measure the absorbance of each solution in a cell of optical path length4cm (seenote to5.4.2), using the spectrometer(4.2) set at the wavelength of maximum absorbance (approximately435nm) or the photometer fitted with the filters specified. Deduct the absorbance of the ze
25、ro standard from the absorbance obtained for each colorimetric solution (see5.4.1). NOTECarry out the measurements immediately after extraction in order to minimize the evaporation of the carbon tetrachloride. 5.4.4 Plotting the calibration curve Plot a graph having, for example, the mass of copper
26、contained in the standard colorimetric solutions (see5.4.1), expressed in micrograms, as abscissae and the corresponding values of absorbance as ordinates. Prepare a new calibration curve whenever a new stock solution(3.5) is prepared. 5.5 Determination 5.5.1 Preparation of the test solution Add the
27、 test portion(5.2) to a600mL beaker, and add350mL of cold water and50.0mL of the hydrochloric acid(3.3). Boil until the sample has completely dissolved. Cool to approximately20 C. Transfer the solution quantitatively to a500mL one-mark volumetric flask, dilute to the mark with water and mix well. NO
28、TEIf the final solution is cloudy, filter it. 5.5.2 Formation of the coloured complex Introduce an aliquot portion of the test solution (see5.5.1) containing0 to10g of copper into a500mL separating funnel and add25.0mL of the zinc dibenzyldithiocarbamate solution(3.4). Stopper, shake well for1min an
29、d allow the layers to separate. Run out the lower layer through a hydrophobic filter paper into a cell of optical path length of4cm. NOTEIf cells of5cm path length have been used to prepare the calibration curve, then use cells of5cm path length for the determination also. 5.5.3 Photometric measurem
30、ents Adjust the apparatus to zero absorbance with respect to carbon tetrachloride(3.2) prior to each measurement. Measure the absorbance, the test solution (see5.5.1) and the blank solution (see5.3) in a cell of optical path length4cm (seenote to5.4.2), using the spectrometer(4.2) set at the wavelen
31、gth of maximum absorbance (approximately435nm) or the photometer fitted with the filters described in4.2. Deduct the absorbance of the blank from the absorbance obtained for the sample. 6 Expression of results Using the calibration curve(5.4.4), determine the mass, in micrograms, of copper in the te
32、st solution and in the blank solution corresponding to the absorbance of the zero standard. Calculate the total copper content, expressed as milligrams per kilogram on a moisture free basis, using the following expression. where m 0 is the mass of the test portion (in g)(5.2); m 1 is the mass of cop
33、per found in the aliquot portion of the test solution (ing)(5.5.2); H is the moisture content determined in accordance with BS7319-2 in% (m/m); V is the volume, in mL, of the aliquot portion of the test solution(5.5.2). 500m 1 () Vm 0 () - 100 100H () - BS7319-7:1990 BSI 11-1999 3 7 Precision Analys
34、es carried out on three samples have been statistically evaluated as shown in Table 2, each laboratory having obtained results by the same operator on two test portions. Table 2 Statistical results of sodium chloride analysis Sample Number of laboratories Mean Standard deviation for Repeatability B
35、r Reproducibility B R mg Cu/kg sample Rock salt 11 0.020 0.0018 0.0153 Vacuum salt 13 0.030 0.0030 0.0159 Sea salt (solid) 13 0.054 0.0083 0.02584 blankBS7319-7:1990 BSI 11-1999 Publications referred to BS998, Specification for vacuum salt for food use 1) . BS3978, Specification for water for labora
36、tory use. BS7319, Analysis of sodium chloride for industrial use. BS7319-1, Method for determination of sodium chloride content 1) . BS7319-2, Method for determination of moisture content. 1) Referred to in the foreword only.BS7319-7: 1990 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandards
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