BS 6068-2 37-1990 Water quality - Physical chemical and biochemical methods - Method for the determination of chloride via a silver nitrate titration with chromate indicator (Mohrs.pdf

1、BRITISH STANDARD BS6068-2.37: 1990 ISO9297:1989 Water quality Part 2: Physical, chemical and biochemical methods Section2.37 Method for the determination of chloride via a silver nitrate titration with chromate indicator (Mohrs method)BS6068-2.37:1990 This British Standard, having been prepared unde

2、r the direction of the Environment andPollution Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 30September1990 BSI04-1999 The following BSI references relate to the work on this standard: Committee reference EPC/44 Draft for comment88/50947

3、DC ISBN 0 580 18754 3 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Environment and Pollution Standards Policy Committee (EPC/-) to Technical Committee EPC/44, upon which the following bodies were represented: Association of Consulting

4、 Scientists British Association for Chemical Specialities British Gas plc Chemical Industries Association Department of the Environment for Northern Ireland Department of the Environment (Water Directorate) Department of Trade and Industry (Laboratory of the Government Chemist) Electricity Supply In

5、dustry in England and Wales Industrial Water Society Institute of Petroleum Institution of Gas Engineers Institution of Water and Environmental Management National Rivers Authority Royal Institute of Public Health and Hygiene Royal Society of Chemistry Scottish Association of Directors of Water and

6、Sewerage Services Soap and Detergent Industry Association Water Companies Association Water Research Centre Water Services Association of England and Wales Amendments issued since publication Amd. No. Date CommentsBS6068-2.37:1990 BSI 04-1999 i Contents Page Committees responsible Inside front cover

7、 National foreword ii 1 Scope 1 2 Normative references 1 3 Principle 1 4 Reagents 1 5 Apparatus 2 6 Procedure 2 7 Expression of results 2 8 Test report 3 Table 1 Interferences 1 Table 2 Precision data 3 Publication(s) referred to Inside back coverBS6068-2.37:1990 ii BSI 04-1999 National foreword Thi

8、s Section of BS6068, which has been prepared under the direction of the Environment and Pollution Standards Policy Committee, is identical with ISO9297:1989 “Water quality Determination of chloride Silver nitrate titration with chromate indicator (Mohrs method)”. The International Standard was prepa

9、red by subcommittee2, Physical, chemical and biochemical methods, of Technical Committee147, Water quality, of the International Organization for Standardization (ISO) with the active participation and approval of the UK. NOTEThe tests described in this Section of BS6068 should only be carried out i

10、n laboratories with suitable facilities and by qualified persons with an appropriate level of chemical expertise. Standard chemical procedures should be followed throughout. BS6068 is being published in a series of Parts subdivided into Sections that will generally correspond to particular internati

11、onal standards. Sections are being, or will be, published in Parts1to7, which, together with Part0, are listed below. Part 0: Introduction; Part 1: Glossary; Part 2: Physical, chemical and biochemical methods; Part 3: Radiological methods; Part 4: Microbiological methods; Part 5: Biological methods;

12、 Part 6: Sampling; Part 7: Precision and accuracy. The Technical Committee has reviewed the provisions of ISO385-1, which is referred to in the text, and has decided that they are acceptable for use in conjunction with this standard. A related British Standard to ISO385-1 is BS846 “Specification for

13、 burettes”. Cross-references International standard Corresponding British Standard BS6068Water quality ISO5667-1:1980 Section6.1:1981Guidance on the design of sampling programmes (Identical) ISO5667-2:1982 Section6.2:1983Guidance on sampling techniques (Identical) ISO5667-3:1985 Section6.3:1986Guida

14、nce on the preservation and handling of samples (Identical) ISO5725:1986 BS5497Precision of test methods Part1:1987 Guide for the determination of repeatability and reproducibility for a standard test method by interlaboratory tests (Identical)BS6068-2.37:1990 BSI 04-1999 iii A British Standard does

15、 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 front cover, an insid

16、e front cover, pagesi to iv, pages1to4, 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.iv blankISO9297:1989(E) BSI 04-1999 1 1 Scope 1.1 Appli

17、cation range This International Standard specifies a titration method for the determination of dissolved chloride in water. The method is applicable to the direct determination of dissolved chloride in concentrations between5mg/l and150mg/l. The working range may be extended to400mg/l by using a bur

18、ette of larger capacity or by sample dilution. Due to many interferences the method is not applicable to heavily polluted waters of low chloride content. 1.2 Interferences Normal concentrations of common constituents of ground water, surface water and potable water do not interfere with the determin

19、ation. The following substances interfere with the method Substances forming insoluble silver compounds, such as bromides, iodides, sulfides, cyanides, hexacyanoferrates(II) and hexacyanoferrates(III). If necessary, bromide and iodide ions shall be determined separately, and the result of the chlori

20、de determination corrected accordingly. Compounds forming complexes with silver ions, such as ammonium and thiosulfate ions. Compounds which will reduce chromate ions, including iron(II) and sulfite ions. The interferences mentioned above will lead to high chloride values. Highly coloured or turbid

21、solutions may obscure the end point, for example hydrated iron oxide. Table 1 Interferences Table 1 gives a summary of the concentrations of interfering compounds, in milligrams per litre, that give an increase of approximately2% in the result when in the presence of70mg/l of chloride. 2 Normative r

22、eferences The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Internationa

23、l Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO385-1:1984, Laboratory glassware Burettes Part1: General requirements. ISO5667-1:19

24、80, Water quality Sampling Part1: Guidance on the design of sampling programmes. ISO5667-2:1982, Water quality Sampling Part2: Guidance on sampling techniques. ISO5667-3:1985, Water quality Sampling Part3: Guidance on the preservation and handling of samples. ISO5725:1986, Precision of test methods

25、Determination of repeatability and reproducibility for a standard test method by inter-laboratory tests. 3 Principle Reaction of chloride with added silver ions to form insoluble silver chloride which precipitates quantitatively. Addition of a small excess of silver ions to form a red brown silver c

26、hromate with chromate ions that have been added as an indicator. This reaction is used for indicating the end-point. The pH is maintained in the range of5to9,5throughout the titration in order to allow precipitation. 4 Reagents NOTE 1All silver compounds and solutions are sensitive to light. Silver

27、salts temporarily stain the skin brown. Use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1 Silver nitrate, standard volumetric solution, c(AgNO 3 ) 0,02mol/l. Dissolve3,3974g of silver nitrate (AgNO 3 ), previously dried at105 C in water and

28、dilute to1000ml in a one-mark volumetric flask. Substance Amount interfering mg/l Br 3 I 5 S 2 0,8 CN 1 Fe(CN) 6 4 2 Fe(CN) 6 3 2 NH 4 + 100 S 2 O 3 2 200 SO 3 2 70 SCN 3 CrO 4 2 1 000 PO 4 3 25ISO9297:1989(E) 2 BSI 04-1999 If stored in the dark in a brown glass bottle with glass stoppers, the solut

29、ion is stable for several months. The solution is standardized against10ml sodium chloride standard reference solution (diluted to100ml) using the procedure given in6.1, however, there is no need for pH adjustment. 4.2 Potassium chromate, indicator,100g/l solution. Dissolve10g of potassium chromate

30、(K 2 CrO 4 ) in water and dilute to100ml. 4.3 Sodium chloride, standard reference solution, c(NaCl)=0,02mol/l. Dissolve1,168 8g of sodium chloride (NaCl), previously dried at105 C, in water and dilute to1 000ml in a one-mark volumetric flask. 4.4 Nitric acid, c(HNO 3 ) 0,1mol/l. Stored in a glass bo

31、ttle, the solution is stable indefinitely. 4.5 Sodium hydroxide, solution, c(NaOH) 0,1mol/l. 4.6 Reagent, for improvement of the buffer capacity. Calcium carbonate (CaCO 3 ) or sodium hydrogen carbonate (NaHCO 3 ) in powder form. 5 Apparatus Ordinary laboratory equipment and 5.1 Burette, of capacity

32、25ml, complying with ISO385-1. 6 Procedure For sampling and preservation of samples refer to ISO5667-1, ISO5667-2 and ISO5667-3. 6.1 Titration Pipette a test portion of100ml, or a smaller volume of the sample diluted to100ml (volume V a ), into either a white porcelain basin, or a conical flask or a

33、 beaker held against a white background. If the pH of the sample is outside the range of5to9,5, adjust the pH using nitric acid(4.4) or sodium hydroxide(4.5) as appropriate, and note the volume required. If ammonium ions are present in the sample in concentrations exceeding10mg/l, adjust the pH to b

34、etween6,5and7. Adjust the pH in one aliquot, then take another and, this time without measuring the pH, add the same amounts of acid/hydroxide solution. NOTE 2If the pH is less than5, pH-adjustment with calcium carbonate or sodium hydrogen carbonate(4.6) is preferable. This will also improve the buf

35、fer capacity. The amount added should be chosen so that a carbonate residue is left in the sample even after titration. Add1ml of potassium chromate indicator solution(4.2). Titrate the solution by dropwise addition of silver nitrate solution until the colour of the solution just changes to a reddis

36、h brown (volume V s ). After addition of one drop of sodium chloride solution(4.3), the colour should disappear. Use the titrated sample treated with sodium chloride solution for comparison with the next titrations. Where the titrant volume exceeds25ml, repeat the determination using a larger capaci

37、ty burette or a smaller test portion volume. 6.2 Blank test Titrate a blank solution as described in6.1, using100ml of water instead of the test sample. The blank value should not exceed0,2ml of4.1. Otherwise check the purity of the water. 7 Expression of results 7.1 Calculation The chloride content

38、 Cl , in milligrams per litre, is given by the formula where Report the result to the nearest1mg/l, giving three significant figures only. 7.2 Precision The precision of the method is given in Table 2. 1) Cl is the concentration, in milligrams per litre, of chloride; V a is the volume, in millilitre

39、s, of the test sample (maximum100ml; dilutions must be taken into account); V b is the volume, in millilitres, of the silver nitrate solution used for the titration of the blank; V s is the volume, in millilitres, of the silver nitrate solution(4.1) used for the titration of the sample; c is the act

40、ual concentration, expressed in moles of AgNO 3 per litre, of the silver nitrate solution; f is the conversion factor, f 35453mg/mol. 1) Values taken from an interlaboratory trial carried out in Germany, F.R., in1983in accordance with ISO5725, except that the method to reject outliers was different.

41、 Cl V s V b ()cf V a - =ISO9297:1989(E) BSI 04-1999 3 8 Test report The test report shall include the following information: a) a reference to this International Standard; b) all information necessary for a complete identification of the sample; c) the results and the method of expression a used; d)

42、 details of any operations not included in this International Standard or regarded as optional, together with any circumstances that may have affected the results. Table 2 Precision data Sample L N x B r CV r B R CV R mg/l mg/l mg/l % mg/l % Drinking water 11 44 12,57 12,75 0,213 1,7 0,572 4,5 Drink

43、ing water, with chloride ions added 9 36 63,79 64,20 0,372 0,6 0,787 1,2 Municipal waste water 10 39 106,4 106,6 0,676 0,6 1,287 1,2 where L is the number of laboratories; x is the true value; is the reproducibility standard deviation; B r is the repeatability standard deviation; N is the number of

44、values; is the mean value; CV R is the reproducibility variation coefficient; CV r is the repeatability variation, coefficient. x x4 blankBS6068-2.37:1990 BSI 04-1999 Publication(s) referred to See national foreword.BSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | | | | | |

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