1、BRITISH STANDARD BS7319-9: 1990 Analysis of sodium chloride for industrial use Part9: Method for determination of mercury contentBS7319-9:1990 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 30September1990 BSI11-1999 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 18542 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 (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 CommentsBS7319-9:1990 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagent
6、s 1 4 Apparatus 2 5 Procedure 2 6 Expression of results 3 7 Precision 3 Figure 1 Typical apparatus for determination of mercury by atomic absorption spectrometry 4 Table 1 Mass of mercury in standard solutions 3 Table 2 Statistical results of sodium chloride analysis 3 Publication(s) referred to Ins
7、ide back coverBS7319-9:1990 ii BSI 11-1999 Foreword BS7319 has been prepared under the direction 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 BS9
8、98:1990. The methods for determination were previously published as appendices to BS998:1969, but did not include a method for mercury. A 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. A B
9、ritish 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 British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a f
10、ront cover, an inside front cover, pagesi andii, pages1 to4, an inside back cover 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.BS7319-9:1990 BSI 11-1999 1 1 Scop
11、e This Part of BS7319 describes a cold vapour atomic absorption spectrometric method for the determination of total mercury in sodium chloride. The method is applicable to products having mercury contents greater than0.02mg of mercury per kilogram of sodium chloride. NOTEThe titles of the publicatio
12、ns 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 a mixture of water, sodium chlorate and hydrochloric acid; b) the conversion of all forms of mercury to ionic
13、 mercury(II) by the chlorine generated; 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
14、 a measuring cell; f) the measurement of the absorbance at a wavelength of approximately253.7nm 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 an
15、alytical grade having the lowest possible mercury content and only water complying with grade3 of BS3978. Store all the reagent solutions in glass bottles. 3.2 Sodium chloride, with a mercury content of lower than0.02mg/kg. 3.3 Hydrochloric acid solution, containing220g/L HCl, approximately, (azeotr
16、opic mixture) Dilute hydrochloric acid solution, =1.19g/mL,(440g/L HCl approximately) with an equal volume of water. Add to each litre,5mL of sulphuric acid, =184g/mL and distil. 3.4 Sodium chlorate solution,100g/L solution. Dissolve100g of sodium chlorate, NaClO 3 , in1000mL of water. 3.5 Potassium
17、 dichromate solution,4g/L solution. Dissolve4g of potassium dichromate, K 2 Cr 2 O 7 , in500mL of water. Add500mL of nitric acid, =1.40g/mL and mix. 3.6 Tin(II) chloride solution. Dissolve25g of tin(II) chloride dihydrate, SnCl 2 .2H 2 O, in50mL of warm hydrochloric acid solution, =1.19g/mL. Allow t
18、o cool and add1g to2g of metallic tin. Dilute to250mL with water and mix. Prepare this solution freshly just before use. Pass a gentle stream of nitrogen through the solution for30min, in order to remove any mercury, before use. NOTEAvoid oxidation of solid tin(II) chloride by air. 3.7 Hydroxylammon
19、ium chloride solution. Dissolve100g of hydroxylammonium chloride, NH 2 OH.HCl, in1000mL water. 3.8 Mercury stock solution, corresponding to1000mg/L mercury. Weigh, to the nearest0.001g,1.354g of mercury (II) chloride, HgCl 2 , into a250mL beaker. Add50mL of the hydrochloric acid solution(3.3) and50m
20、L of the potassium dichromate solution(3.5). Transfer the solution quantitatively to a1000mL one-mark volumetric flask, dilute to the mark with water and mix. Store this solution in a cool, dark place and renew after2months. 3.9 Mercury, standard solution, corresponding to1mg/LHg. Prepare this solut
21、ion on the day of use by successive dilution of the stock solution(3.8). The final solution shall contain50mL of potassium dichromate solution(3.5) per litre of water. 3.10 Charcoal 3.11 Drying agent, e.g.anhydrous calcium sulphate(3mm to5mm, for desiccant use) 1) . 3.12 Air or nitrogen. Use air or
22、nitrogen containing no mercury or other components absorbing radiation at a wave length of approximately253.7nm. As an additional precaution, introduce a charcoal filter before the aeration flask (see Figure 1). 1) For information on the availability of other drying agents, apply to Enquiry Section,
23、 BSI, Linford Wood, Milton Keynes MK146LE.BS7319-9:1990 2 BSI 11-1999 4 Apparatus NOTEAn example of a suitable apparatus is shown in Figure 1. This depicts an open-circuit measuring system and includes4.1 to4.9. 4.1 Atomic absorption spectrometer, fitted with a low-pressure mercury vapour lamp or a
24、mercury hollow-cathode lamp. 4.2 Recorder or integrating read-out, giving full deflection in less than1s. 4.3 Measuring cell, minimum optical path length10cm, with windows transparent to radiation at253.7nm. 4.4 Aeration flask, for example a100mL gas washing bottle, with a sintered glass or fine jet
25、 inlet tube and a mark at60mL. NOTEIf several bottles are used, check that identical results are obtained with each. 4.5 Four-way stopcock 4.6 Flow control system 4.7 Conical flasks,100mL. 4.8 Adsorber, filled with the charcoal(3.10), for the removal of mercury vapour from the exhaust gases. Length
26、approximately100mm, internal diameter approximately15mm. 4.9 Adsorber, filled with drying agent(3.11). Length approximately100mm, internal diameter approximately15mm. 5 Procedure 5.1 General Wash all glassware not previously used for this determination, including flasks used for reagents and samples
27、, as follows rinsing with water after each operation: a) with a brush and detergent if the walls are greasy; b) with aqua regia or with nitric acid solution, =1.42g/mL. Before using the glassware thus washed for actual determinations, check it by carrying out several blank tests until satisfactory r
28、esults are obtained. Thereafter use such glassware for mercury determinations only. After each 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 aera
29、tion flask are removed by rinsing with hydrochloric acid =1.19g/L. All connecting tubes 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 nearest0.1g, approximately10g of the test sample, tr
30、ansfer it to a100mL conical flask and add30mL of water. NOTEThe sample solution prepared according to BS7319-3 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. Car
31、ry out the determination described in5.5. 5.3 Blank test Transfer to a100mL conical flask30mL of water. Proceed in accordance with5.5, 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
32、) add the same quantity of the sodium chloride(3.2) as the test portion(5.2),30mL of water and the volumes of the standard mercury solution(3.9) indicated in Table 1. Carry out the determination described in5.5. NOTE 1Because of matrix effects, dependent on the concentration of sodium chloride in th
33、e solution during aeration (see5.5.3), a quantity of sodium chloride equal to the test portion (see5.2) 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
34、 sodium chloride, using the method of standard additions. 5.5 Determination 5.5.1 Mineralization Add to each of the conical flasks (see5.2, 5.3 and5.4) some glass beads and4.0mL of the hydrochloric acid solution(3.3) and3.0mL of the sodium chlorate solution(3.4). Dissolve the sodium chloride, heat t
35、o boiling, continue boiling for5min and allow to cool to room temperature. Transfer the solution quantitatively to a100mL one-mark volumetric flask, dilute to the mark with water and mix. Immediately before the measurement described in5.5.3, transfer10.0mL of this solution to the aeration flask, fol
36、lowed by3mL of the hydroxylammonium chloride solution(3.7). 5.5.2 Apparatus settings The settings of the atomic absorption spectrometer are as follows. Air or nitrogen flow:60L/h Wavelength:253.7nmBS7319-9:1990 BSI 11-1999 3 Table 1 Mass of mercury in standard solutions Adjust the spectrometer(4.1)
37、according to the manufacturers instructions. 5.5.3 Measurement Dilute the contents of the aeration flask to the60mL mark with water. Add2mL of the tin(II) chloride solution(3.6) and immediately connect the flask to the apparatus (see Figure 1). Swirl to mix and allow to stand for some minutes. Pass
38、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 aeration flask. 5.5.4 Preparation of the calibration curve Deduct the absorbance of the zero standard from
39、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 corresponding values of absorbance as ordinates. 6 Expression of results Using the calibration curve (see
40、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, expressed in micrograms of mercury (Hg) per kilogram on a moisture free basis, using the following expression. 7 P
41、recision 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 each sample. Table 2 Statistical results of sodium chloride analysis Volume of the standard mercury soluti
42、on(3.9) Corresponding mass of mercury mL 0 a 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 m 1 is the mass of mercury in the test portion (see5.2) (ing); m 2 is the mass of mercury in the blank solution (see5.3) (ing); m 0 is the mass of the test portion (see5.2) (ing); H is the
43、 moisture content as determined in accordance with BS7319-2in%(m/m). m 1 m 2 m 0 - 100 100H () - Sample Number of laboratories Mean Standard deviation for Repeatability r Reproducibility R Rock salt 14 mg Hg/kg sample 6.2 3.98 24.10 Vacuum salt 12 3.3 2.78 11.42 Sea salt 12 4.6 3.12 15.98BS7319-9:19
44、90 4 BSI 11-1999 Figure 1 Typical apparatus for determination of mercury by atomic absorption spectrometryBS7319-9:1990 BSI 11-1999 Publication(s) referred to BS998, Specification for vacuum salt for food use 2) . BS3978, Specification for water for laboratory use. BS7319, Analysis of sodium chlorid
45、e for industrial use. BS7319-1, Method for determination of sodium chloride content. BS7319-2, Method for determination of moisture content. BS7319-3, Method for determination of matter insoluble in water or in acid. 2) Referred to in the foreword only.BS7319-9: 1990 BSI 389 Chiswick High Road Londo
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