1、BRITISH STANDARD BS7319-11: 1990 Analysis of sodium chloride for industrial use Part11: Method for determination of iron contentBS7319-11:1990 This BritishStandard, having been prepared under the directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Board of BS
2、Iandcomes intoeffect on 30 September1990 BSI11-1999 The following BSI references relate to the work on this standard: Committee references CIC/22, FAC/23 Draft for comment88/55624DC ISBN 0 580 18544 3 Committees responsible for this BritishStandard The preparation of this BritishStandard was entrust
3、ed 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 Re
4、search Council (FRCA) 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 Mil
5、k Marketing Board for Northern Ireland Royal Association of British Dairy Farmers Salt Manufacturers Association Amendments issued since publication Amd. No. Date CommentsBS7319-11:1990 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagen
6、ts 1 4 Apparatus 1 5 Procedure 1 6 Expression of results 3 7 Precision 3 Table 1 Mass of iron in standard solutions 2 Table 2 Expected iron content 2 Publication(s) referred to Inside back coverBS7319-11:1990 ii BSI 11-1999 Foreword BS7319 has been prepared under the direction of the Chemicals Stand
7、ards 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 list of the Parts of BS
8、7319 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 It supersedes Appendix K of BS998:1969 which is withdrawn. A British Standard does not purport to include all the necessary provisions of a contract. Users of Briti
9、sh 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 cover and a back cover. Th
10、is 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.BS7319-11:1990 BSI 11-1999 1 1 Scope This Part of BS7319 specifies a photometric method, using1,10-phenanthroline, for the determination
11、 of iron in sodium chloride. The method is applicable to products having iron contents equal to or greater than1mg/kg. NOTEThe titles of the publications referred to in this Part of this BritishStandard are listed on the inside back cover. 2 Principle The principles of this Part of BS7319 are as fol
12、lows: a) the reduction of trivalent iron by hydroxylammonium chloride; and the formation of a coloured complex between divalent iron and1,10-phenanthroline in a buffered medium; b) the photometric measurement of the coloured complex at a wavelength of approximately510nm. 3 Reagents 3.1 General. Use
13、only reagents of recognized analytical grade and only water complying with grade3 of BS3978. 3.2 Hydrochloric acid, =1.19g/mL,37%(m/m) solution approximately. 3.3 Acetic acid glacial, =1.05g/mL,99% to100%(m/m) solution. 3.4 Hydroxylammonium chloride solution. Dissolve10g of hydroxylammonium chloride
14、 (NH 2 OH.HCl) in1L of water. 3.5 1,10-phenanthroline solution. Dissolve2.5g of1,10-phenanthroline hydrochloride monohydrate (C 12 H 8 N 2 .HCl.H 2 O) in1L of water. NOTEThis compound may be replaced by2.1g of 1,10-phenanthroline monohydrate (C 12 H 8 N 2 .H 2 O). 3.6 Sodium acetate solution. Dissol
15、ve500g sodium acetate trihydrate (CH 3 COONa.3H 2 O) in water and dilute to1L. 3.7 Buffer solution. Dissolve272g of sodium acetate trihydrate (CH 3 COONa.3H 2 O)(3.6) in approximately500mL of water. Add240mL of the acetic acid(3.3) to the solution. Transfer quantitatively to a1000mL one-mark volumet
16、ric flask, dilute to the mark with water and mix well. This solution has a pH of4.9. 3.8 Iron stock solution, corresponding to0.20g/L Fe. Dissolve1.4043g of ammonium iron (II) sulphate hexahydrate (NH 4 ) 2 Fe(SO 4 ) 2 .6H 2 O, weighed to the nearest0.0001g, in200mL of water. Add20mL of sulphuric ac
17、id solution( =about1.84g/mL) and cool to ambient temperature. Transfer to a1000mL one-mark volumetric flask, dilute to the mark with water and mix well. 1 mL of this solution contains 200 g of Fe. 3.9 Iron standard solution, corresponding to0.010g/L Fe. Transfer25.0mL of the standard iron solution(3
18、.8) to a500mL one-mark volumetric flask, dilute to the mark with water and mix well. 1mL of this solution contains10g of Fe. Prepare this solution at the time of use. 4 Apparatus 4.1 Ordinary laboratory equipment 4.2 Spectrometer, or photometer, fitted with filters which provide a transmission maxim
19、um between500nm and520nm. 4.3 pH meter equipped with a glass electrode and a calomel reference electrode, or pH indicator paper, covering the pH range3.5 to4.2 and indicating in0.2pH unit intervals. 5 Procedure CAUTION. Ensure that no trace of iron is introduced during the analysis by the reagents,
20、the water or the apparatus, 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 detergent if the sides are greasy; b) with concentrated nitric acid, followed by several rinses with water. 5
21、.2 Test portion Weigh, to the nearest0.01g, a test portion of approximately10g. 5.3 Blank test At the same time as the determination carry out a blank test following the same procedure and using the same quantities of all the reagents used for the determination but omitting the test portion. 5.4 Pre
22、paration of the calibration curve 5.4.1 Preparation of standard colorimetric solutions Add the volumes of the standard iron solution(3.9) given in Table 1 to a series of five100mL one-mark volumetric flasks. Dilute the solution in each flask to approximately50mL with water, and then add the followin
23、g: a) 0.5mL of the hydrochloric acid solution(3.2); b) 5mL of the hydroxylammonium chloride solution(3.4);BS7319-11:1990 2 BSI 11-1999 c) 5mL of the1,10-phenanthroline solution(3.5); d) 25mL of the buffer solution(3.7). Dilute to the mark with water, mix well and allow the solution to stand for10min
24、. Table 1 Mass of iron in standard solutions 5.4.2 Photometric measurements Adjust the apparatus to zero absorbance with respect to water prior to each measurement. Measure the absorbance of each solution in a cell of optical path length4cm (see note) using the spectrometer(4.2) set at the wavelengt
25、h of maximum absorbance (approximately510nm), or the photometer fitted with the filters specified. Deduct the absorbance of the zero standard from the absorbance obtained for the other standards. NOTECells of path length5cm may be used if4cm cells are not available. 5.4.3 Plotting the calibration cu
26、rve Plot a graph having, for example, the masses of iron contained in100mL of 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 is prepared. 5.5 D
27、etermination 5.5.1 Preparation of the test solution Add the test portion(see5.2) to a suitable size beaker (for example400mL) and add25mL of hydrochloric acid solution(3.2) and approximately100mL of water. Boil until the sample has completely dissolved, and for a further5min. Cool to ambient tempera
28、ture. Transfer the solution quantitatively to a500mL one-mark volumetric flask, dilute to the mark with water and mix well. 5.5.2 Adjustment of pH 5.5.2.1 Selection of aliquot portions Take two aliquot portions of the test solution (see5.5.1) according to the expected iron content, as indicated in T
29、able 2. Table 2 Expected iron content Add the first aliquot portion to a beaker of suitable size (for example100mL), and the second to a100mL one-mark volumetric flask. 5.5.2.2 Preliminary pH check Dilute the aliquot portion in the beaker to about50mL. Then add the following: a) 5mL of the hydroxyla
30、mmonium chloride solution(3.4); b) 5mL of the1,10 phenanthroline solution(3.5); c) 25mL of the buffer solution(3.7). Check the pH of the solution with the pH meter or paper indicator(4.3). The value shall be between3.5 and4.2. If the value is not in this range, adjust the pH by adding slowly, stirri
31、ng after each addition, either the necessary amount of the acetic acid solution(3.3) or the necessary amount of the sodium acetate solution(3.6). Record the amount of reagent needed to adjust the pH and reject the solution. 5.5.3 Formation of the coloured complex Add the same amounts of all the reag
32、ents used for the preliminary test(see5.5.2.2) to the aliquot portion in the volumetric flask. Dilute to100mL, mix and allow to stand for10 min. 5.5.4 Photometric measurements Adjust the apparatus to zero absorbance with respect to water prior to each measurement. Measure the absorbance of the test
33、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 wavelength of maximum absorbance (approximately510nm), or the photometer fitted with the filters described in4.2. Deduct the absorbance of the blank from t
34、he absorbance obtained for the sample. NOTEIf5cm cells were used to prepare the calibration graph, use5cm cells here also. Standard iron solution(3.9) Corresponding mass of iron mL 0 a 2.5 5.0 10.0 15.0 g 25 50 100 150 a Zero standard. Expected iron content Volume of aliquot portion mg/kg Fe 100 100
35、 to250 250 to500 500 mL 50 25 10 5BS7319-11:1990 BSI 11-1999 3 6 Expression of results Using the calibration curve(5.4.3) determine the mass, in micrograms, of iron in the test solution and in the blank solution, corresponding to the absorbance of the zero standard. Calculate the iron content, expre
36、ssed as milligrams of per kilogram on a moisture free basis, using the following expression. 7 Precision A collaborative study to determine the precision of this method has not been undertaken. where m 0 is the mass of the test portion (see5.2) (in g); m 1 is the mass of iron found in the test solut
37、ion(see5.5) (in g); m 2 is the mass of iron found in the blank test solution(see5.3) (in g); V is the volume of the aliquot portion of the test solution(see5.5.2.1) (in mL); H is the moisture content determined in accordance with BS7319-2 in%(m/m). m 1 m 2 m 0 - 500 V - 100 100 H () -4 blankBS7319-1
38、1:1990 BSI 11-1999 Publication(s) referred to BS998, Specification for vacuum salt for food use 1) . BS3978, Specification for water for laboratory use. BS7319, Analysis of sodium chloride for industrial use. BS7319-1, Method for determination of sodium chloride content. BS7319-2, Method for determi
39、nation of moisture content. 1) Referred to in the foreword only.BS7319-11: 1990 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 internati
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