1、BRITISH STANDARD BS7319-6: 1990 Analysis of sodiumchloride forindustrial use Part 6: Method for determination of cadmium contentBS7319-6:1990 This BritishStandard, having been prepared under the directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Board ofBSIa
2、ndcomes into effect on 30 September1990 BSI 12-1999 The following BSI references relate to the work on this standard: Committee references CIC/22, FAC/23 Draft for comment88/55619DC ISBN 0 580 18539 7 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 (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 Mil
5、k Marketing Board for Northern Ireland Royal Association of British Dairy Farmers Salt Manufacturers Association Amendments issued since publication Amd. No. Date CommentsBS7319-6:1990 BSI 12-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagent
6、s 1 4 Apparatus 1 5 Procedure 1 6 Expression of results 3 7 Precision 3 Table 1 Mass of cadmium in standard solutions 2 Table 2 Statistical results of sodium chloride analysis 3 Publications referred to Inside back coverBS7319-6:1990 ii BSI 12-1999 Foreword BS7319 has been prepared under the directi
7、on 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.
8、A list of all 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. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible f
9、or 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 to 4, an inside back cover and a back cover. This standard has been updated
10、(see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7319-6:1990 BSI 12-1999 1 1 Scope This Part of BS7319 describes a flame atomic absorption spectrometric (AAS) method for the determination of total cadmium in sodi
11、um chloride. 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 follows: a) the mineralization of cadmium and dissolution of the sample in nitric acid solution; b) the compl
12、exation of the cadmium and certain other metals by ammonium pyrrolidine-1-carbodithioate, and extraction of the metal complexes into chloroform and back-extraction into nitric acid; c) aspiration of the nitric acid solution into an acetylene-air flame; d) measurement of the absorbance at a wavelengt
13、h of about228.8nm, using an atomic absorption spectrometer fitted with a cadmium hollow-cathode lamp. 3 Reagents 3.1 General. Unless otherwise stated, use only reagents of recognized analytical grade and water complying with grade3 of BS3978. 3.2 Nitric acid, =1.40g/mL,945 g/L HNO 3approximately. 3.
14、3 Chloroform, =1.481g/mL. 3.4 Ammonium pyrrolidine-1-carbodithioate (APCD) solution, special reagent for AAS. Dissolve20g AAS grade APCD in1 L of water and filter. Prepare this solution daily. 3.5 Ammonia solution, =0.9g/mL. 3.6 Diammonium hydrogen citrate solution, 113g/L solution. Dissolve124g dia
15、mmonium hydrogen citrate in a500mL one-mark volumetric flask, dilute to the mark with water and mix. Purify this solution as follows. Shake100mL of the solution with10mL of the APCD solution(3.4) and extract three times respectively with10mL,5ml and5mL of the chloroform(3.3). Back-extract the combin
16、ed organic extracts into nitric acid, as follows. After the phase separation following each extraction, run the organic layer into a previously dried100mL separating funnel(4.5) containing1.0mL nitric acid(3.2). a) Repeat the extraction and back extraction procedure until, when aspirating the nitric
17、 extracts into the acetylene-air flame, the absorbance measured at approximately228.8nm is lower than10 times the absorbance of20mL of chloroform extracted into a mixture of1.0mL nitric acid(3.2) and9.0mL water. b) Transfer100mL of the purified solution into a200mL one-mark volumetric flask, add20mL
18、 ammonia solution(3.5), dilute to the mark with water and mix. 3.7 Cadmium, stock solution, corresponding to1000mg/L. Weigh, to the nearest0.0001g,1.000g of cadmium metal strip or granules(99.99%) and dissolve them in10mL of the nitric acid(3.2). Transfer the solution quantitatively to a1000mL one-m
19、ark volumetric flask, dilute to the mark with water and mix. NOTE 11mL of this solution contains1mg of lead. NOTE 2A commercial stock solution for atomic absorption spectrometry of the same strength may also be used if available. 3.8 Cadmium, standard solution, corresponding to5mg/L. Transfer5.0mL o
20、f the stock solution(3.7) to a1000mL one-mark volumetric flask, add1.0mL of the nitric acid(3.2), and then dilute to the mark with water and mix. 4 Apparatus 4.1 Ordinary laboratory apparatus 4.2 Atomic absorption spectrometer, fitted with an acetylene-air burner and scale expansion facility. NOTEIn
21、 order to reduce the interferences caused by non-atomic absorption the use of a background correction device is recommended. 4.3 Cadmium hollow-cathode lamp 4.4 Separating funnels of 500mL capacity. 4.5 Separating funnels of 100mL capacity. 5 Procedure 5.1 General NOTEEnsure that no traces of cadmiu
22、m are introduced during the analysis, taking care to avoid any contamination by traces of cadmium during the sampling process. Wash all the glassware to be employed for this determination as follows, rinsing very carefully with water after each operation: a) with a brush and detergent if the walls a
23、re greasy; b) with diluted nitric acid(1 : 2). 5.2 Test portion Weigh, to the nearest1g, a test portion of250g.BS7319-6:1990 2 BSI 12-1999 5.3 Test solution Transfer the test portion (see5.2) into a2000mL beaker, add850mL of water and stir to dissolve. 5.4 Blank test Transfer850mL water into a2000mL
24、 beaker to act as a blank solution. 5.5 Mineralization To each2000mL beaker (see5.3 and5.4) add10.0mL of the nitric acid(3.2) and stir. Add some glass beads, heat to the boil and boil gently for30min. Ensure that the total volume never falls below800mL, adding more water if necessary. (The same volu
25、me to both beakers.) Allow the solution to cool and transfer it quantitatively to a1000mL one-mark volumetric flask, dilute to the mark with water and mix. 5.6 Determination 5.6.1 Preparation of the standard matching solutions 5.6.1.1 Preparation of the standard matching solution for the test soluti
26、on Transfer into each of four500mL separating funnels(4.4)200mL of the mineralized test solution (see5.5) and the volumes of the standard cadmium solution(3.8) indicated in Table 1. Table 1 Mass of cadmium in standard solutions Complex and extract cadmium as described in5.6.2.2 to5.6.2.6. 5.6.1.2 Pr
27、eparation of the standard matching solutions for the blank Transfer to four50mL one-mark volumetric flasks the volumes of the standard cadmium solution(3.8) indicated in Table 1. To each flask add5.0mL of nitric acid(3.2), dilute to the mark with water and mix. Carry out the procedure described in5.
28、6.4. 5.6.2 Complexation and extraction of cadmium 5.6.2.1 Transfer200mL of the mineralized blank solution (see5.5) to a500mL separating funnel(4.4). 5.6.2.2 Carry out the procedure with this500mL separatory funnel and the four500mL separating funnels from5.6.1.1 as follows. a) Add20.0mL of the diamm
29、onium hydrogen citrate solution(3.6). b) Add5.0mL of the APCD solution(3.4), shake for30s. c) Add10.0mL of the chloroform(3.3), shake vigorously for1min. 5.6.2.3 After phase separation run the organic layer into a previously dried100mL separating funnel(4.5) containing1.0mL of nitric acid(3.2). 5.6.
30、2.4 Repeat this extraction procedure twice, using5mL of chloroform(3.3) each time and combining the organic phases in the separating funnel(4.5). 5.6.2.5 Shake the separating funnel vigorously for30s, add9.0mL of water and shake vigorously for1min. 5.6.2.6 When the layers have separated discard the
31、lower organic layer and transfer the upper aqueous layer to a dry tube. NOTEThe solution thus obtained may also be used for the determination of lead. (See BS7319-8.) 5.6.3 Apparatus setting Equip the spectrometer(4.1) with the cadmium lamp(4.2). Set the lamp current, the slit and the pressure of ac
32、etylene and air according to the instrument manufacturers instructions. Adjust the wavelength to that of the maximum absorption at approximately228.8nm. 5.6.4 Spectrometric measurements Aspirate all the final solutions (see5.6.2) and the standard matching solutions for the blank (see5.6.1.2) into th
33、e acetylene-air flame in the following order, and at the same time, determine the absorbance of each. a) The four standard matching solutions for the blank test solution (see Table 1). b) The final blank test solution(5.4) after the complexation and extraction. c) The three final standard matching s
34、olutions for the test solution after the complexation and extraction of cadium (numbers2,3 and4 from Table 1). d) The final test solution after the complexation and extraction of cadium (number1 form Table 1). Standard matching solution reference number Volume of the standard cadmium solution(3.8) C
35、orresponding mass of cadmium 1 a 2 3 4 mL 0.00 0.50 1.00 2.00 g 0.0 2.5 5.0 10.0 a Test solution.BS7319-6:1990 BSI 12-1999 3 Aspirate water after each measurement. 6 Expression of results 6.1 Calculation 6.1.1 Calibration factors 6.1.1.1 Calibration factors for the test solution The calibration fact
36、ors (f 1 ) of the three standard matching solutions for the test solution (see Table 1) is given by the following formula: 6.1.1.2 Calibration factor for the blank test solution The calibration factor (f 3 ) of the three standard matching solutions for the blank test (see5.6.1.2) is given by the fol
37、lowing formula: 6.1.2 Average calibration factors The average calibration factors are the arithmetic mean of each group of the three calibration factors found in6.1.1.1. 6.1.3 Cadmium content The cadmium content, expressed in milligrams of cadmium (Cd) per kilogram of sodium chloride on a moisture f
38、ree basis, is given by the following formula:7 Precision Analyses carried out on three samples led to the statistical results shown in Table 2, each laboratory having furnished results obtained by the same operator performing two analyses on each sample. Table 2 Statistical results of sodium chlorid
39、e analysis where m 1 is the mass of cadmium added to the standard matching solution (seenumbers2,3 and4 from Table 1) (ing); A 1 is the absorbance obtained for each final standard matching solution; A 2 is the absorbance of the final test solution. where m 1 is the mass of cadmium added to the stand
40、ard matching solution (seenumbers2,3 and4 from Table 1) (ing); A 3 is the absorbance obtained for each standard matching solution; f 1 m 1 A 1 A 2 - = f 3 m 1 A 3 A 4 - = A 4 is the absorbance of the standard matching solution. where A 2 is the absorbance measured for the final test solution; A 5 is
41、 the absorbance measured for the final blank test solution; f 1m is the average calibration factor (see6.1.2) for the test solution; f 3m is the average calibration factor (see6.1.2) for the blank test solution. m is the mass of the test portion(5.1) (ing); H is the moisture content, determined in a
42、ccordance with BS7319-2 in% (m/m) Sample Number of laboratories Mean Standard deviation for Repeatability r Reproducibility R Rock salt 14 mg Cd/kg sample 0.002 0.0010 0.0011 Vacuum salt 15 0.001 0.0054 0.0104 Sea salt 15 0.011 0.0022 0.01024 blankBS7319-6:1990 BSI 12-1999 Publications referred to B
43、S998, 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 1) . BS7319-2, Method for determination of moisture content. 1) Referred to
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