1、BRITISH STANDARD BS7319-8: 1990 Analysis of sodiumchloride forindustrial use Part8: Method for determination oflead contentBS7319-8:1990 This BritishStandard, having been prepared under the directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Board ofBSIandcom
2、es into effect on 28September1990 BSI12-1999 The following BSI references relate to the work on this standard: Committee references CIC/22, FAC/23 Draft for comment88/55622 DC ISBN 0 580 18541 9 Committees responsible for this BritishStandard The preparation of this BritishStandard was entrusted by
3、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 Research
4、 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 Milk Mark
5、eting Board for Northern Ireland Royal Association of British Dairy Farmers Salt Manufacturers Association Amendments issued since publication Amd. No. Date CommentsBS7319-8:1990 BSI 12-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagents 1 4
6、Apparatus 1 5 Procedure 1 6 Expression of results 3 7 Precision 3 Table 1 Mass of lead in standard solutions 2 Table 2 Statistical results of sodium chloride analysis 3 Publication(s) referred to Inside back coverBS7319-8:1990 ii BSI 12-1999 Foreword BS7319 has been prepared under the direction of t
7、he 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 list
8、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 It supersedes Appendix N of BS998:1969 which is withdrawn. A British Standard does not purport to include all the necessary provisions of a contra
9、ct. 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 cover an
10、d 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.BS7319-8:1990 BSI 12-1999 1 1 Scope This Part of BS7319 describes a flame atomic absorption spectrometric (AAS) method
11、 for the determination of total lead in sodium 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 dissolution of the sample in nitric acid solution
12、; b) the complexation of certain metals, including lead, by ammonium pyrrolidine-1-carbodithioate, and extraction of the metal complexes into chloroform and back-extraction into nitric acid; c) the aspiration of the nitric acid solution into an acetylene/air flame; d) the measurement of the absorban
13、ce at a wavelength of approximately283.3nm, using an atomic absorption spectrometer fitted with a lead 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,945g/mL
14、HNO 3approximately. 3.3 Chloroform, =1.48g/mL. 3.4 Ammonium pyrrolidine-1-carbodithioate solution, special reagent for AAS. Dissolve20g of AAS grade APCD in1L of water and filter. Prepare this solution daily. 3.5 Ammonia solution, =0.9g/mL. 3.6 Diammonium hydrogen citrate solution, 113g/L solution.
15、Dissolve124g of diammonium hydrogen citrate in a500mL one-mark volumetric flask, dilute to the mark with water and mix. Purify this solution as follows. a) Shake100mL of the solution with10mL of the APCD solution(3.4) and extract three times respectively with10mL,5mL and5mL of the chloroform(3.3). b
16、) After the phase separation, following each extraction, back-extract the combined organic extracts into nitric acid by running the organic layer into a previously dried100mL separating funnel(4.5) containing1.0mL of the nitric acid(3.2). c) Repeat the extraction and back-extraction procedure until,
17、 when aspirating the nitric acid extracts into the acetylene-air flame, the absorbance measured at approximately283.3nm is lower than10times the absorbance of20mL of chloroform extracted with a mixture of1.0mL of the nitric acid(3.2) and9.0mL of water. d) Transfer the purified solution to a200mL one
18、-mark volumetric flask, add20mL of the ammonia solution(3.5), dilute to the mark with water and mix. 3.7 Lead stock solution, corresponding to1000mg/LPb. Weigh, to the nearest0.0001g,1.598g of lead nitrate, Pb(NO 3 ) 2 , grind it and dissolve it in10mL of the nitric acid(3.2). Transfer the solution
19、quantitively to a1000mL one-mark volumetric flask, dilute to the mark with water and mix. NOTE 11mL of this solution contains0.001g of lead. NOTE 2A commercial stock solution for atomic absorption spectrometry of the same strength may also be used, if available. 3.8 Lead standard solution, correspon
20、ding to10mg/LPb. Transfer10.0mL of the lead stock solution(3.5) to a1000mL one-mark volumetric flask, add1.0mL of 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 an
21、d scale expansion facility. NOTEIn order to reduce interferences caused by non-atomic absorption the use of a background correction device recommended. 4.3 Lead hollow-cathode lamp 4.4 Separating funnels,500mL. 4.5 Separating funnels,100mL. 5 Procedure 5.1 General NOTEEnsure that no traces of lead a
22、re introduced during the analysis, taking care to avoid any contamination during the sampling process and particularly at the grinding stage. 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
23、 if the walls are greasy; b) with diluted nitric acid(1:2). 5.2 Test portion Weigh, to the nearest1g, a test portion of250g.BS7319-8:1990 2 BSI 12-1999 5.3 Test solution Transfer the test portion (see5.2) to a2000mL beaker, add850mL of water and swirl to dissolve. 5.4 Blank test Transfer850mL water
24、into a2000mL 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 boiling and boil gently for30min. Ensure that the total volume never falls below800mL, adding more water if necessary. (Th
25、esame volume 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 solutions for the
26、test solution Transfer into each of four500mL separating funnels(4.4)200mL of the mineralized test solution (see5.5) and the volumes of the standard lead solution(3.8) indicated in Table 1. Complex and extract lead as described in5.6.2.2 to5.6.2.6. 5.6.1.2 Preparation of the standard matching soluti
27、ons for the blank Transfer to four50mL one-mark volumetric flasks the volumes of the lead standard solution indicated in Table 1. To each flask add5.0mL of the nitric acid(3.2), dilute to the mark with water and mix. Carry out the procedure as described in5.6.4. 5.6.2 Complexation and extraction of
28、lead 5.6.2.1 Transfer200mL of the mineralized blank solution (see5.5) to a500mL separating funnel(4.4). Table 1 Mass of lead in standard solutions 5.6.2.2 Carry out the procedure with this500mL separating funnel (see5.6.2.1) and the four from5.6.1.1 in the following way. a) Add20.0mL of the diammoni
29、um hydrogen citrate solution(3.6). b) Add5.0mL of the APCD solution(3.4) and shake for30s. c) Add10.0mL of the chloroform(3.3) and 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 the nitric acid(3.2
30、). 5.6.2.4 Repeat this extraction procedure twice, using5mL of the chloroform(3.2) 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 d
31、iscard the 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 cadmium. (See BS7319-6.) 5.6.3 Apparatus setting Equip the spectrometer(4.2) with the lead hollow-cathode lamp(4.3). Set the lamp current, the s
32、lit and the pressure of acetylene and air according to the instrument manufacturers instructions. Adjust the wavelength to that of the maximum absorption at approximately283.3nm. 5.6.4 Spectrometric measurement Aspirate all the final solutions (see5.6.2) and the standard matching solutions for the b
33、lank (see5.6.1.2) into the 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 (seeTable 1). b) The final blank test solution (see5.4) after the complexation and extraction of lead. St
34、andard matching solution reference number Volume of the standard lead solution(3.8) Corresponding mass of lead 1 a 2 3 4 mL 0 2.5 5.0 10.0 g 0 25 50 100 a Test solutions.BS7319-8:1990 BSI 12-1999 3 c) The three final standard matching solutions for the test solution after the complexation and extrac
35、tion of lead. d) The final test solution after5.6.2 (number1 from Table 1). 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 factors (f 1 ) of the three standard matching solutio
36、ns for the test solution (seeTable 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 following formula: 6.1.2 Average calibration factors
37、The average calibration factors are the arithmetic mean of each group of the three calibration factors found in6.1.1.1. 6.1.3 Lead content The lead content, expressed in milligrams of lead (Pb) per kilogram of sodium chloride on a moisture free basis, is given by the following formula: 7 Precision A
38、nalyses carried out on three samples led to the statistical results given 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 chloride analysis where m 1 is the mass of lead added to the stan
39、dard matching solution (see numbers2,3 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 lead added to the standard matching solution (see numbers2,3 and4 from Table 1) (ing);
40、f 1 m 1 A 1 A 2 - = f 3 m 1 A 3 A 4 - = A 3 is the absorbance obtained for each standard matching solution; 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 the absorbance measured for the final blank test solution; m i
41、s the mass of the test portion (see5.2) (ing); H is the moisture content determined in accordance with BS7319-2. in%(m/m). 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. Sample Number of laborato
42、ries Mean Standard deviation for Repeatability r Reproducibility R Rock salt 15 mgPb/kg sample 0.045 0.0566 0.1299 Vacuum salt 14 0.025 0.0483 0.1566 Sea salt 15 0.808 0.1254 0.41414 blankBS7319-8:1990 BSI 12-1999 Publication(s) referred to BS998, Specification for vacuum salt for food use 1) . BS39
43、78, 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 determination of moisture content. BS7319-6, Method for determination of cadmium content. 1) Referred to in the
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