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1、BRITISH STANDARD BS 7319-9: 1990 Analysis of sodium chloride for industrial use Part 9: Method for determination of mercury content Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7319-9:1990 This British St
2、andard, having been prepared under the direction of the Chemicals Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 30 September 1990 BSI 11-1999 The following BSI references relate to the work on this standard: Committee references CIC/22, FA
3、C/23 Draft for comment 88/55622 DC ISBN 0 580 18542 7 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Chemicals Standards Policy Committee (CIC/-) to Technical Committee CIC/22, upon which the following bodies were represented: British A
4、ssociation for Chemical Specialities Chemical Industries Association Man-made Fibres Producers Committee Soap and Detergent Industry Association Textile Research Council (FRCA) The following bodies were also represented in the drafting of the standard, through Technical Committee FAC/23: AFRC Instit
5、ute of Food Research Creamery Proprietors Association Department of Trade and Industry (Laboratory of the Government Chemist) Food and Drink Federation Milk Marketing Board for Northern Ireland Royal Association of British Dairy Farmers Salt Manufacturers Association Amendments issued since publicat
6、ion Amd. No.DateComments Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7319-9:1990 BSI 11-1999i Contents Page Committees responsibleInside front cover Forewordii 1Scope1 2Principle1 3Reagents1 4Apparatus2
7、5Procedure2 6Expression of results3 7Precision3 Figure 1 Typical apparatus for determination of mercury by atomic absorption spectrometry4 Table 1 Mass of mercury in standard solutions3 Table 2 Statistical results of sodium chloride analysis3 Publication(s) referred toInside back cover Licensed Copy
8、: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7319-9:1990 ii BSI 11-1999 Foreword BS 7319 has been prepared under the direction of the Chemicals Standards Policy Committee, at the request of Technical Committee FAC/23,
9、 Salt, primarily to provide appropriate methods for determination of vacuum salt for food use as specified in BS 998:1990. The methods for determination were previously published as appendices to BS 998:1969, but did not include a method for mercury. A list of the Parts of BS 7319 is given in Part 1
10、. This Part of BS 7319 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 for their correct application. Compliance with a Br
11、itish Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendment
12、s incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7319-9:1990 BSI 11-19991 1 Scope This Part of BS 7319 describes a cold
13、 vapour atomic absorption spectrometric method for the determination of total mercury in sodium chloride. The method is applicable to products having mercury contents greater than 0.02 mg of mercury per kilogram of sodium chloride. NOTEThe titles of the publications referred to in this Part of this
14、British Standard are listed on the inside back cover. 2 Principle The principles of this Part of BS 7319 are as follows: a) the dissolution of the sample in a mixture of water, sodium chlorate and hydrochloric acid; b) the conversion of all forms of mercury to ionic mercury (II) by the chlorine gene
15、rated; c) the reduction of the excess of oxidant by hydroxylammonium chloride; d) the reduction of the mercury (II) to atomic mercury by tin (II) chloride; e) the entrainment of the mercury in a stream of gas and passage of the gas containing the mercury vapour through a measuring cell; f) the measu
16、rement of the absorbance at a wavelength of approximately 253.7 nm using an atomic absorption spectrometer fitted with a low-pressure mercury vapour lamp or a mercury hollow cathode lamp. 3 Reagents 3.1 General. Unless otherwise stated, use only reagents of recognized analytical grade having the low
17、est possible mercury content and only water complying with grade 3 of BS 3978. Store all the reagent solutions in glass bottles. 3.2 Sodium chloride, with a mercury content of lower than 0.02 mg/kg. 3.3 Hydrochloric acid solution, containing 220 g/L HCl, approximately, (azeotropic mixture) Dilute hy
18、drochloric acid solution, = 1.19 g/mL, (440 g/L HCl approximately) with an equal volume of water. Add to each litre, 5 mL of sulphuric acid, = 184 g/mL and distil. 3.4 Sodium chlorate solution, 100 g/L solution. Dissolve 100 g of sodium chlorate, NaClO3, in 1 000 mL of water. 3.5 Potassium dichromat
19、e solution, 4 g/L solution. Dissolve 4 g of potassium dichromate, K2Cr2O7, in 500 mL of water. Add 500 mL of nitric acid, = 1.40 g/mL and mix. 3.6 Tin (II) chloride solution. Dissolve 25 g of tin (II) chloride dihydrate, SnCl2.2H2O, in 50 mL of warm hydrochloric acid solution, = 1.19 g/mL. Allow to
20、cool and add 1 g to 2 g of metallic tin. Dilute to 250 mL with water and mix. Prepare this solution freshly just before use. Pass a gentle stream of nitrogen through the solution for 30 min, in order to remove any mercury, before use. NOTEAvoid oxidation of solid tin (II) chloride by air. 3.7 Hydrox
21、ylammonium chloride solution. Dissolve 100 g of hydroxylammonium chloride, NH2OH.HCl, in 1 000 mL water. 3.8 Mercury stock solution, corresponding to 1 000 mg/L mercury. Weigh, to the nearest 0.001 g, 1.354 g of mercury (II) chloride, HgCl2, into a 250 mL beaker. Add 50 mL of the hydrochloric acid s
22、olution (3.3) and 50 mL of the potassium dichromate solution (3.5). Transfer the solution quantitatively to a 1 000 mL one-mark volumetric flask, dilute to the mark with water and mix. Store this solution in a cool, dark place and renew after 2 months. 3.9 Mercury, standard solution, corresponding t
23、o 1 mg/L Hg. Prepare this solution on the day of use by successive dilution of the stock solution (3.8). The final solution shall contain 50 mL of potassium dichromate solution (3.5) per litre of water. 3.10 Charcoal 3.11 Drying agent, e.g. anhydrous calcium sulphate (3 mm to 5 mm, for desiccant use
24、)1). 3.12 Air or nitrogen. Use air or nitrogen containing no mercury or other components absorbing radiation at a wave length of approximately 253.7 nm. As an additional precaution, introduce a charcoal filter before the aeration flask (see Figure 1). 1) For information on the availability of other
25、drying agents, apply to Enquiry Section, BSI, Linford Wood, Milton Keynes MK14 6LE. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7319-9:1990 2 BSI 11-1999 4 Apparatus NOTEAn example of a suitable apparatu
26、s is shown in Figure 1. This depicts an open-circuit measuring system and includes 4.1 to 4.9. 4.1 Atomic absorption spectrometer, fitted with a low-pressure mercury vapour lamp or a mercury hollow-cathode lamp. 4.2 Recorder or integrating read-out, giving full deflection in less than 1 s. 4.3 Measu
27、ring cell, minimum optical path length 10 cm, with windows transparent to radiation at 253.7 nm. 4.4 Aeration flask, for example a 100 mL gas washing bottle, with a sintered glass or fine jet inlet tube and a mark at 60 mL. NOTEIf several bottles are used, check that identical results are obtained w
28、ith each. 4.5 Four-way stopcock 4.6 Flow control system 4.7 Conical flasks, 100 mL. 4.8 Adsorber, filled with the charcoal (3.10), for the removal of mercury vapour from the exhaust gases. Length approximately 100 mm, internal diameter approximately 15 mm. 4.9 Adsorber, filled with drying agent (3.1
29、1). Length approximately 100 mm, internal diameter approximately 15 mm. 5 Procedure 5.1 General Wash all glassware not previously used for this determination, including flasks used for reagents and samples, as follows rinsing with water after each operation: a) with a brush and detergent if the wall
30、s are greasy; b) with aqua regia or with nitric acid solution, = 1.42 g/mL. Before using the glassware thus washed for actual determinations, check it by carrying out several blank tests until satisfactory results are obtained. Thereafter use such glassware for mercury determinations only. After eac
31、h use treat the aeration flasks with the potassium dichromate solution (3.5), in order to oxidize any traces of tin (II) that they may contain. Traces of tin (IV) oxide which may adhere to the walls of the aeration flask are removed by rinsing with hydrochloric acid = 1.19 g/L. All connecting tubes
32、shall be as short as possible, in order to reduce adsorption of mercury. Keep the aeration flasks full of water when not in use. 5.2 Test portion Weigh, to the nearest 0.1 g, approximately 10 g of the test sample, transfer it to a 100 mL conical flask and add 30 mL of water. NOTEThe sample solution
33、prepared according to BS 7319-3 should not be used, as in this solution mercury losses will occur. Samples should be mixed as well as possible and the test portion should be taken directly from the solid sample blend. Carry out the determination described in 5.5. 5.3 Blank test Transfer to a 100 mL
34、conical flask 30 mL of water. Proceed in accordance with 5.5, using the same quantities of all the reagents as used for the determination. 5.4 Preparation of the standard matching solutions To a series of six conical flasks (4.7) add the same quantity of the sodium chloride (3.2) as the test portion
35、 (5.2), 30 mL of water and the volumes of the standard mercury solution (3.9) indicated in Table 1. Carry out the determination described in 5.5. NOTE 1Because of matrix effects, dependent on the concentration of sodium chloride in the solution during aeration (see 5.5.3), a quantity of sodium chlor
36、ide equal to the test portion (see 5.2) should be taken for the preparation of standard matching solutions. NOTE 2Samples of unknown composition should be tested for the presence of matrix effects caused by components present other than sodium chloride, using the method of standard additions. 5.5 De
37、termination 5.5.1 Mineralization Add to each of the conical flasks (see 5.2, 5.3 and 5.4) some glass beads and 4.0 mL of the hydrochloric acid solution (3.3) and 3.0 mL of the sodium chlorate solution (3.4). Dissolve the sodium chloride, heat to boiling, continue boiling for 5 min and allow to cool
38、to room temperature. Transfer the solution quantitatively to a 100 mL one-mark volumetric flask, dilute to the mark with water and mix. Immediately before the measurement described in 5.5.3, transfer 10.0 mL of this solution to the aeration flask, followed by 3 mL of the hydroxylammonium chloride so
39、lution (3.7). 5.5.2 Apparatus settings The settings of the atomic absorption spectrometer are as follows. Air or nitrogen flow: 60 L/h Wavelength: 253.7 nm Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 731
40、9-9:1990 BSI 11-19993 Table 1 Mass of mercury in standard solutions Adjust the spectrometer (4.1) according to the manufacturers instructions. 5.5.3 Measurement Dilute the contents of the aeration flask to the 60 mL mark with water. Add 2 mL of the tin (II) chloride solution (3.6) and immediately co
41、nnect the flask to the apparatus (see Figure 1). Swirl to mix and allow to stand for some minutes. Pass air or nitrogen (3.12) through the aeration flask by manipulating the four-way stopcock. Continue the gas flow until no mercury is left in the system then switch off the gas flow and remove the ae
42、ration flask. 5.5.4 Preparation of the calibration curve Deduct the absorbance of the zero standard from the absorbance obtained for the other standards. Plot a graph having, for example, the mass of mercury contained in the standard matching solutions, expressed in micrograms, as abscissae and the
43、corresponding values of absorbance as ordinates. 6 Expression of results Using the calibration curve (see 5.5.4), determine the mass, in micrograms, of mercury in the test solution and in the blank solution corresponding to the absorbance of the zero standard. Calculate the mercury content, expresse
44、d in micrograms of mercury (Hg) per kilogram on a moisture free basis, using the following expression. 7 Precision Analyses 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
45、each sample. Table 2 Statistical results of sodium chloride analysis Volume of the standard mercury solution (3.9) Corresponding mass of mercury mL 0a 0.5 1.0 1.5 2.0 3.0 g 0 0.5 1.0 1.5 2.0 3.0 a Zero standard. where m1is the mass of mercury in the test portion (see 5.2) (in g); m2is the mass of me
46、rcury in the blank solution (see 5.3) (in g); m0is the mass of the test portion (see 5.2) (in g); His the moisture content as determined in accordance with BS 7319-2 in % (m/m). m1m2 m0 - 100 100H() - - Sample Number of laboratories Mean Standard deviation for Repeatability rReproducibility R Rock s
47、alt14 mg Hg/kg sample 6.2 3.9824.10 Vacuum salt123.32.7811.42 Sea salt124.63.1215.98 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7319-9:1990 4 BSI 11-1999 Figure 1 Typical apparatus for determination of
48、mercury by atomic absorption spectrometry Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7319-9:1990 BSI 11-1999 Publication(s) referred to BS 998, Specification for vacuum salt for food use2). BS 3978, Spe
49、cification for water for laboratory use. BS 7319, Analysis of sodium chloride for industrial use. BS 7319-1, Method for determination of sodium chloride content. BS 7319-2, Method for determination of moisture content. BS 7319-3, Method for determination of matter insoluble in water or in acid. 2) Referred to in the foreword only. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:34:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7319-9: 1990 BSI 389 Chi
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